CA2033687C - Recording method for magneto-optic memory medium - Google Patents
Recording method for magneto-optic memory mediumInfo
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- CA2033687C CA2033687C CA002033687A CA2033687A CA2033687C CA 2033687 C CA2033687 C CA 2033687C CA 002033687 A CA002033687 A CA 002033687A CA 2033687 A CA2033687 A CA 2033687A CA 2033687 C CA2033687 C CA 2033687C
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- memory medium
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10502—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing characterised by the transducing operation to be executed
- G11B11/10515—Reproducing
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10502—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing characterised by the transducing operation to be executed
- G11B11/10517—Overwriting or erasing
- G11B11/10519—Direct overwriting, i.e. performing erasing and recording using the same transducing means
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/1055—Disposition or mounting of transducers relative to record carriers
- G11B11/1058—Flying heads
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10582—Record carriers characterised by the selection of the material or by the structure or form
- G11B11/10586—Record carriers characterised by the selection of the material or by the structure or form characterised by the selection of the material
Abstract
A recording method for a magneto-optic memory medium of an exchange-coupled type having a recording layer with a low Curie point and a high coercive force and a reading layer with a high Curie point and a low coercive force, which comprises the steps of applying a magnetic field to the magneto-optic memory medium to develop predetermined data in the reading layer, and then applying both an optical beam and a magnetic field to the magneto-optic memory medium for writing the predetermined data in the recording layer. The data is simultaneously verified on the basis of a Kerr effect of the optical beam caused by the reading layer.
Description
The present invention relates to a recording method for a magneto-optic memory medium, and more particularly, to a recording method for a magneto-optic memory medium including an overwriting to the magneto-optic memory medium by the use of a magnetic field modulating process, wherein the writing and verifying of data is simultaneously performed.
A thin film of an amorphous rare earth-transition metal alloy, such as GdCo, TbFe, GdNdFe, GdTbFe and the like (hereinafter abbreviated as RE-TM film) has been used as a memory medium in a magneto-optic disc device since it has suitable characteristics for magneto-optic recording.
Particularly known is a magneto-optic memory medium having an exchange-coupled double-layered structure in which a recording layer of a low Curie point and a high coercive force and a reading layer of a high Curie point and a low coercive force are laminated to improve the reading efficiency of written data ("MagnetizationProcess ofExchange-Coupled Ferrimagnetic Double-Layered Films", Japanese Journal of Applied Physics, 20:11:2089-2095; November, 1981).
Recording in the exchange-coupled magneto-optic memory medium is performed by applying an optical beam for heating and a magnetic field to the memory medium to write predetermined data in the writing layer. After writing (and cooling), the data is automatically transcribed to and stably retained in the reading layer having a high Kerr effect due to exchange-coupling by magnetization. Hence, reading can be stably carried out by the use of a Kerr effect of the reading layer which provides an excellent reading efficiency.
Rewriting in the magneto-optic memory medium is carried out usually by the steps (1) erasing old data, (2) writing new data, and (3) verification or confirmation of the written data. The art at the primitive stage turns the disc once for each of the above steps, so that the disc is required to turn three times during each rewriting operation.
In this regard, the so-called overwriting tP~n;que, indispensable for high speed recording of information, has been positively studied. A magnetic field modulation process is presently regarded as the most readily available and ~- A effective overwriting t~c-hn;que.
`- 2033687 The overwriting terhn;que, which allows data to be overwritten, performs the aforesaid steps (1) and (2) simultaneously, thereby increasing the speed of the recording process.
5However, the verification step (3) must be conducted in such a manner that the memory medium is first cooled enough to cause data in the recording layer to be fully transcribed to the reading layer before the data can be read therefrom to be checked. Hence, one more turn of the disc is required for the verification step after the overwriting. While it is desirable to further increase the speed of the recording process, the verification step is indispensable for ensuring the reliability of the written data and cannot practically be omitted.
15An object of the present invention is to provide a recording method for a magneto-optic memory medium to perform the aforesaid three steps of rewriting simultaneously and realizing a high speed recording process.
According to one aspect of the present invention, there is provided a recording method for a magneto-optic memory medium of exchange-coupled type having a recording layer of a low Curie point and high coercive force and a reading layer of a high Curie point and low coercive force, which comprises the steps of:
25applying a magnetic field to the magneto-optic memory medium to develop a predetermined data in the reading layer, and then applying both an optical beam and a magnetic field to the magneto-optic memory medium for writing the predetermined data in the recording layer, and simultaneously verifying the data upon said writing on the basis of a Kerr effect of the optical beam caused by the reading layer.
According to another aspect of the present invention, there is provided a recording method for a magneto-optic memory medium of exchange-coupled type having a recording layer with a low Curie point and a high coercive ~ ......
" 2033687 force of a GdTbFe amorphous alloy thin film wherein the GdTbFe amorphous alloy is represented by the following formula:
(GdpTb1p)qFe1q wherein 0.l < q < 0.35, o < p x q < 0.25, o < (l-p) x q <
0.25, and a reading layer with a high Curie point and a low coercive force of a GdNdFe amorphous alloy thin film wherein the GdNdFe amorphous alloy is represented by the following formula:
GdXNdyFe1-x-y wherein 0.l < x < 0.3 and 0 < y < 0.25, which method comprises the steps of applying a magnetic field to the magneto-optic memory medium to develop predetermined data in the reading layer, and subsequently applying both an optical beam and a magnetic field to the magneto-optic memory medium for writing the predetermined data in the recording layer, and simultaneously verifying the data upon said writing on the basis of a Kerr effect of the optical beam caused by the reading layer.
According to the present invention, the coercive force of the reading layer (hereinafter referred to as the first layer) in the magneto-optic memory medium is lower, at around room temperature, than the force of the external magnetic field for writing and the coercive force of the recording layer (hereinafter referred to as the second layer and typically having a force about 200 kOe higher than the first layer). Hence, the direction of magnetization in the first layer quickly becomes the same as that of the external magnetic field without an increase in temperature by the optical beam when the external magnetic field for writing, which is modulated corresponding to recording signals, is applied. As a result, information (predetermined data) is transcribed to the first layer. In this instance, the first layer exhibits a Kerr rotation angle at a level readily detected at a recording (writing) temperature, so that the information transcribed into the first layer is detected on the basis of the Kerr effect of an optical beam applied to the memory medium, specifically to the second layer, for the writing operation. The detected magneto-optic signal is used for verification of the aforesaid information.
Simultaneously with the verification step, the second layer is heated by the optical beam to a temperature near its Curie temperature, and the same information is written when the magnetic field for writing is applied to the second layer, so that the writing and verification steps are conducted simultaneously.
Since the second layer has a higher coercive force, it becomes a stable data-retaining layer at room temperature after the writing step.
Also, the coercive force of the first layer, at around room temperature, is lower than that of the second layer, so that the direction of magnetization of the first layer follows and is stably retained by the second layer as a result of the exchange-coupling force generated between the first and second layers, thereby making the first layer (the reading layer) and the second layer (the recording layer) to be stable record-keeping layers.
According to the recording method for a magneto-optic memory medium of the present invention, the verification of the recorded information can be carried out simultaneously with the recording and/or overwriting steps, thereby increasing the speed of the recording process by more than two times, in comparison with the conventional art.
In the accompanying drawings which illustrate an embodiment of the present invention:
Figure 1 is a cross-sectional view of a magneto-optic memory medium used in the present invention;
Figure 2 is a graphical representation of the temperature dependency of a magneto-optic characteristic measured from the first layer side of the recording layers of the magneto-optic memory medium;
Figure 3 is a graphical representation of the temperature dependency of a magneto-optic characteristic measured from the second layer side of the recording layers of the magneto-optic memory medium;
Figure 4 is a graphical representation of the hysteresis characteristic of the magneto-optic memory medium to an external magnetic field;
Figure 5 is a schematic diagram illustrating a principle of the magneto-optic recording;
Figure 6 is an illustration of a waveform of detected signals on the basis of a Kerr effect of an optical beam upon writing;
Figure 7 is an illustration of a conventional waveform of detected signals on the basis of a Kerr effect of an optical beam upon writing;
Figure 8 is a graphical representation of the compositional dependency of a magneto-optic characteristic of a GdNdFe amorphous alloy film;
Figure 9 is a graphical representation of the compositional dependency of the other magneto-optic characteristic of a GdNdFe amorphous alloy film;
Figure 10 is a graphical representation of the compositional dependency of a magneto-optic characteristic of a TbFeCo amorphous alloy film; and Figure 11 is a graphical representation of the compositional dependency of a magneto-optic characteristic of a DyFeCo amorphous alloy film.
The exchange-coupled magneto-optic memory medium used in the present invention comprises a specific recording layer and a specific reading layer, the layers being laminated on an appropriate substrate. It is usually preferable that the reading layer and the recording layer are formed in this order on a transparent substrate. Preferably the substrate has an intervening first dielectric film of SiN, AlN, ZnS, sio2, SiAlON, AlNGe and the like. Preferably, the recording layer is coated with a second dielectric film.
The recording layer and the reading layer may employ known various amorphous rare earth-transition metal alloy thin films which are applied to an exchange-coupled magneto-optic "' ~A
20~687 memory medium. It is preferable that the reading layer has a Curie temperature greater than that of the underlying recording layer and the recording temperature, upon application of the optical beam. Preferably, the reading layer has a Kerr rotation angle of a readily detectable level at the writing temperature, and has a coercive force, at around room temperature, lower than the magnetic field for writing and the coercive force of the recording layer.
It is particularly preferable that the recording layer is made of GdTbFe amorphous alloy thin film and the reading layer of GdNdFe amorphous alloy thin film.
It is preferable that the recording layer comprises an amorphous alloy thin film represented by the following formula:
(GdpTbl p)qFe1 q wherein p and q satisfy the inequalities 0.1 < q < 0.35, 0 < p x q < 0.25, 0 < (1 - p) x q < 0.25, and the reading layer comprises an amorphous alloy thin film represented by the following formula:
GdXNdyFe1-x-y wherein x and y satisfy the inequalities 0.1 < x < 0.3 and o < y < 0.25.
These amorphous alloy thin films may be formed by sputtering or deposition, for example, the sputtering process using a target of alloys having corresponding compositions or a composite target in an on-chip type, or a multiple-synchronous deposition process using a multiple source.
A suitable thickness of the recording and reading layers is 5,000 ~ or less. Preferably the thickness is in the range of from about 100 to 1000 ~, in consideration of the effect of the exchange-coupling force and recording sensitivity.
The following Examples illustrate the present invention.
EXAMPLES
Referring now to Figure 1, an example of a suitable structure of a magneto-optic memory medium 1 used in the .~
, .. .
present invention will be detailed. The medium 1 comprises a glass substrate 2 and a dielectric layer 3 made of AlN, a reading layer 4 (the first layer) made of GdNdFe, a recording layer 5 (the second layer) made of GdTbFe, and an another dielectric layer 6 made of AlN, those being formed in this order on the substrate 2 to form a double-layered structure by the reading layer 4 and the recording layer 5.
GdNdFe (forming the reading layer 4) is an amorphous alloy having a Gd:Nd:Fe component ratio of 19.0:4.0:77.0% and a thickness of 200 ~. GdTbFe (forming the recording layer 5) is an amorphous alloy having a Gd:Tb:Fe component ratio of 14.0:14.0:72.0% and a thickness of 600 ~.
The temperature dependency of the coercive force Hc and the Kerr rotation angle ek, which are magneto-optic characteristics of the medium 1 constructed as above, were measured from the side of the reading layer 4 (GdNdFe) and the result is shown in Figure 2 wherein the coercive force Hc is shown by the mark o and the Kerr rotation angle ek by the mark . Figure 2 reveals that the reading layer 4 has a low coercive force Hc and is readily magnetized and inverted to have uniform magnetization direction for substantially the whole temperature range when a magnetic field greater than 200 Oe is applied to the reading layer 4. Also, the reading layer 4 has a high Curie temperature, so that the Kerr rotation angle ek is large and kept at a value 50% or more of that at room temperature at about 160C. In a typical magneto-optic recording, the memory layer is raised to a temperature of about 160C by an optical beam for writing, typically a laser beam. Hence, the GdNdFe reading layer 4 is provided with a Kerr rotation angle ek at a level fully and readily detectable at a writing temperature (for example, higher than 0.1 deg), thereby providing a detected signal having a sufficient intensity.
Likewise, the temperature dependency of the coercive force Hc and the Kerr rotation angle ek, which are magneto-optic characteristics of the medium 1, were measured from the side of the recording layer 5 (GdTbFe) and the result is , .
203368~
illustrated in Figure 3 wherein the coercive force Hc is shown by the mark o and the Kerr rotation angle by the mark .
Figure 3 reveals that the recording layer 5 has a coercive force Hc of about 2 kOe at room temperature and is very small at a writing temperature near 160C. This is due to the low Curie temperature of the GdTbFe. Hence, the GdTbFe recording layer 5 is readily magnetized and inverted to follow the direction of the recording magnetic field when the recording magnetic field is applied to the recording layer 5 at the writing temperature, so that the recorded information can be stably retained at around room temperature.
The double-layered structure enables magnetization direction of the reading layer 4 to follow that of the recording layer 5 as a result of the exchange-coupling action.
Figure 4 shows the hysteresis characteristic of the Kerr rotation angle ek measured from the reading layer side with respect to an external magnetic field H. For measurement, the reading layer 4 and the recording layer 5 where initialized by + 2.0 kOe of an external magnetic field at room temperature and subjected to a series of external magnetic field as follows: 0 ~ + 1.0 kOe - 0 Oe ~ - 1.0 kOe ~ 0 kOe, at 60C
of atmosphere. As shown in Figure 4, the values of the Kerr rotation angle ek are constant when the values of the external magnetic field are positive (the same direction as the initialized magnetization), and are inverted when the value of the external magnetic field is about - 0.2 kOe. When the applied external magnetic field is further varied from - 1.0 kOe to 0 kOe, the value of the Kerr rotation angle would again be inverted at about + 0.2 kOe of the external magnetic field if the reading layer 4 is provided without the recording layer 5. But, the value of the Kerr rotation angle is actually inverted again at about - 0.2 kOe and returns to the original value when the hysteresis loop is closed.
The first inversion of the Kerr rotation angle at about - 0.2 kOe corresponds to the above explanation that the reading layer 4 is readily magnetized and inverted in magnetization direction for substantially the whole temperature range due to an applied magnetic field greater than about 200 Oe. Also, the fact that the value of the external magnetic field H is again inverted at about - 0.2 kOe and returned to the original value when the hysteresis loop is closed results from the fact that, when the external field H (causing the reading layer 4 to be inverted) was weakened, an exchange-coupling force between the reading layer 4 and the recording layer 5 caused the reading layer 4 to be inverted again. Since the coercive force Hc of the recording layer 5 is greater than + 1.0 kOe at the measuring temperature of 60C
as shown in Figure 3, the recording layer 5 is not magnetized and inverted by an external magnetic field in the range + 1.0 kOe to - 1.0 kOe but keeps its initialized direction of magnetization. Also, the coercive force Hc of the recording layer 5 is enough to apply an exchange-coupling force to the reading layer 4.
As discussed earlier, the double-layered structure for recording in the medium 1 allows the exchange-coupling force to be produced in order to follow the magnetization direction of the reading layer 4 to that of the recording layer 5.
When a magnetic field 10, which runs in the direction shown by the arrow A in Figure 5 and is modulated corresponding to the predetermined data, is applied to the memory layer of the double-layered structure comprising the reading layer 4 and the recording layer 5, the magnetization direction of the reading layer 4 becomes substantially identical to that of the recording magnetic field 10 prior to an increase in temperature due to the application of a laser beam 7, so that the information (the predetermined data) is transcribed to the reading layer 4. This is because a coercive force of the reading layer 4 is less than the level of the magnetic field 10, as previously mentioned.
Thereafter, when a modulated magnetic field 10, substantially identical in information to the above, and the laser beam 7 (for example, of from about 4.0 to 10 mW output) are applied to the recording layer 5, the temperature of the recording t A
203~687 layer 5 increases to near the Curie temperature, thereby causing a portion 9 subjected to the elevated temperature to have a reduced coercive force and to be magnetized along the direction of the magnetic field 10.
In turn, the reading layer 4 has a Kerr rotation angle ek high enough to be readily detectable at around the writing temperature, so that a detected signal of a sufficient intensity can be obtained by reflection of the laser beam 7 on the basis of its Kerr rotation angle. Since the recorded information is previously transcribed to the reading layer 4 in the same direction as that of the magnetic field, the signals detected from the transcribed information can be applied to verification of recording information.
The detected signals (output by the use of pick-up) in an actual overwriting by use of a floating magnetic head is described hereinafter. The size of the slider of the magnetic head used in the experiment is 6 x 4 mm2 to allow the slider to flow about 5~m above the surface of medium 1. The magnetic head is 0.3 x 0.2 mm2 and 1 mm in length in a single magnetic pole type with 12 turns of 50~m diameter Cu wire, and the driving current is + 0.4 A. The magnetic field generated by the magnetic head was + 200 Oe.
The detected signals upon overwriting by use of the memory medium 1 of the present invention are shown in Figure 6. The film thickness of the dielectric layer 3 is 800 ~ and those of the reading layer 4 and the recording layer 5 are 200 and 600 ~, respectively, as referred to in the explanation of Figure 1, while that of the dielectric layer 6 is 250 ~. The medium 1, before being overwritten, has been written in by use of recording signals of a single frequency of 1.85 MHz. The tester is adapted to jump one track after writing in every track. The recording signal used for overwriting is of a single frequency of 1.0 MHz.
In view of Figure 6, an overwriting detection signal 13 shown by the thick and sold line and having a large amplitude is obtained upon application of the laser beam of 4.0 mW of recording output, and its frequency corresponds to ,~, that (1.0 MHz) of the recording signals. Hence, it was confirmed that it is possible to verify the written data upon overwriting thereof. For reference, the data previously recorded upon the frequency of 1.8S MHz was reproduced before overwriting by the use of a 4.0 mW laser beam, the result of which is shown as a detecting signal 14 in Figure 6.
The detected signals upon overwriting by use of a conventional magneto-optic memory medium is shown in Figure 7, as a comparative example. A magneto-optic memory medium used in this comparison comprises a four-layered structure including a dielectric layer made of AlN, a recording layer made of GdTbFe, a dielectric layer made of AlN and a reflective layer made of Al, laminated in this order on a glass substrate. Also in the comparative example, the medium, before being overwritten, has been written in by recording signals of 1.85 MHz of a single frequency, and recording signals used for overwriting has 1.0 MHz of a single frequency.
In view of Figure 7, since the Kerr rotation angle ek of the above memory layer is small, the overwriting detection signal 15 shown by the thick and solid line and having a rather small amplitude is obtained upon application of the laser beam of 4.0 mW of recording output, and its frequency corresponds to that (1.85 MHz) of a previous recording signal. Hence, it was confirmed that previously recorded data was detected, which is of no use for verification. For reference, the data previously recorded upon the frequency of 1.85 MHz was reproduced by the use of a laser beam of 4.0 mW, the result of which is also shown as a detecting signal 16 in Figure 7.
The recording method for a magneto-optic memory medium of the present invention is not limited in application to the magneto-optic memory medium having the above-mentioned construction. Various examples of magneto-optic memory mediums applicable to the present invention will be detailed hereinafter.
.
A composition of GdNdFe forming the reading layer 4 will be referred to. A compositional dependency of the coercive force Hc of GdNdFe at room temperature is shown in Figure 8, wherein a characteristic when the composition of Nd is fixed at about 4% is shown by the mark o and that with an Nd composition of about 10% is shown by the mark . In the case where the Nd composition is fixed at about 4%, the coercive force of GdNdFe at room temperature is from about 0.4 to 0.9 kOe, but it is restrained to be less than 0.1 kOe at temperatures greater than 100C. By use of a two-layered structure comprising the reading layer 4 and a GdTbFe recording layer 5, the value of the coercive force Hc at room temperature was about 0.15 kOe within the range of from about 17 to 25% Gd, as shown in Figure 2. Also, the Curie temperature of GdNdFe was generally greater than 190C to fully exceed the writing temperature.
The compositional dependency of the Kerr rotation angle of GdNdFe is shown in Figure 9, wherein a characteristic when the composition of Nd is fixed at about 4% is shown by the mark o , that with an Nd composition of about 10% by the mark , and that with an Nd composition of about 21% by the mark ~ . In the case where the Nd composition is fixed at about 4%, the Kerr rotation angle ek exhibits a high value of about 0.4 within the range of from about 17 to 25% Gd.
As a result, when the composition of Nd in the GdNdFe alloy forming the reading layer 4 is fixed at about 4%, the composition of Gd can be set to be from about 17 to 25%.
Any combinations of the reading layer 4 having a film thickness in the range of from 150 to 600 ~, with the recording layer 5 of a film thickness in the range of from 200 to 600 ~, exhibit a substantially identical characteristic to that disclosed in the present example of the invention, thereby enabling the overwriting and the verification steps to be performed simultaneously.
Also, when the characteristics of GdNdFe of the reading layer 4, such as the coercive force Hc, the Kerr rotation angle ek and the Curie temperature are controlled in 203368~
an optimum range, the magneto-optic memory medium for the recording layer 5 may be made of TbFeCo, DyFeCo, GdTbFeCo and the like.
Another suitable magneto-optic memory medium comprises a glass substrate 2, a dielectric layer 3 which is made of AlN and has a film thickness of about 800 ~, a TbFeCo reading layer 4 having a film thickness of about 200 ~, a recording layer 5 which is made of TbFeCo in a different composition ratio to that of the reading layer 4 and has a film thickness of about 600 ~, and a dielectric layer 6 which is made of AlN with a film thickness of about 250 ~, formed in this order of the glass substrate 2. In this case, the Tb:Fe:Co ratio for the reading layer 4 was 10.0:82.0:8.0%, and that of the recording layer 5 was 24.0:68.0:8.0%. The compositional dependency of the coercive force Hc and the Curie temperature Tc of TbFeCo when a composition ratio of Co is fixed at 8.0% is shown in Figure 10, wherein the compositional dependency of the coercive force Hc is shown by the mark o , and that of the Curie temperature Tc by the mark . Referring to Figure 10, the coercive force Hc of the reading layer 4, with a Tb composition of 10.0%, is about 0.4 kOe. Also, the recording layer 5, with a Tb composition of 24.0%, is substantially compensated in composition. It was confirmed that a magneto-optic memory medium constructed as above can simultaneously permit the overwriting and the verification.
The compositional dependency of the coercive force Hc and the Curie temperature Tc of DyFeCo when the composition of Co is fixed at about 19.0% is shown in Figure 11, wherein the compositional dependency of the coercive force Hc is shown by the mark o , and that of the Curie temperature Tc by the mark . Referring to Figure 11, a composition ratio of DyFeCo forming the reading layer 4 and that of DyFeCo forming the recording layer 5 can be selected with an optimum value similarly to the above TbFeCo.
Although the reading layer 4 and the recording layer may be made of the same material having different -20~368~
compositions, the recording layer 5 may be made of GdTbFe, GdTbFeCo, NdDyFeCo and GdDyFe and the like.
A
A thin film of an amorphous rare earth-transition metal alloy, such as GdCo, TbFe, GdNdFe, GdTbFe and the like (hereinafter abbreviated as RE-TM film) has been used as a memory medium in a magneto-optic disc device since it has suitable characteristics for magneto-optic recording.
Particularly known is a magneto-optic memory medium having an exchange-coupled double-layered structure in which a recording layer of a low Curie point and a high coercive force and a reading layer of a high Curie point and a low coercive force are laminated to improve the reading efficiency of written data ("MagnetizationProcess ofExchange-Coupled Ferrimagnetic Double-Layered Films", Japanese Journal of Applied Physics, 20:11:2089-2095; November, 1981).
Recording in the exchange-coupled magneto-optic memory medium is performed by applying an optical beam for heating and a magnetic field to the memory medium to write predetermined data in the writing layer. After writing (and cooling), the data is automatically transcribed to and stably retained in the reading layer having a high Kerr effect due to exchange-coupling by magnetization. Hence, reading can be stably carried out by the use of a Kerr effect of the reading layer which provides an excellent reading efficiency.
Rewriting in the magneto-optic memory medium is carried out usually by the steps (1) erasing old data, (2) writing new data, and (3) verification or confirmation of the written data. The art at the primitive stage turns the disc once for each of the above steps, so that the disc is required to turn three times during each rewriting operation.
In this regard, the so-called overwriting tP~n;que, indispensable for high speed recording of information, has been positively studied. A magnetic field modulation process is presently regarded as the most readily available and ~- A effective overwriting t~c-hn;que.
`- 2033687 The overwriting terhn;que, which allows data to be overwritten, performs the aforesaid steps (1) and (2) simultaneously, thereby increasing the speed of the recording process.
5However, the verification step (3) must be conducted in such a manner that the memory medium is first cooled enough to cause data in the recording layer to be fully transcribed to the reading layer before the data can be read therefrom to be checked. Hence, one more turn of the disc is required for the verification step after the overwriting. While it is desirable to further increase the speed of the recording process, the verification step is indispensable for ensuring the reliability of the written data and cannot practically be omitted.
15An object of the present invention is to provide a recording method for a magneto-optic memory medium to perform the aforesaid three steps of rewriting simultaneously and realizing a high speed recording process.
According to one aspect of the present invention, there is provided a recording method for a magneto-optic memory medium of exchange-coupled type having a recording layer of a low Curie point and high coercive force and a reading layer of a high Curie point and low coercive force, which comprises the steps of:
25applying a magnetic field to the magneto-optic memory medium to develop a predetermined data in the reading layer, and then applying both an optical beam and a magnetic field to the magneto-optic memory medium for writing the predetermined data in the recording layer, and simultaneously verifying the data upon said writing on the basis of a Kerr effect of the optical beam caused by the reading layer.
According to another aspect of the present invention, there is provided a recording method for a magneto-optic memory medium of exchange-coupled type having a recording layer with a low Curie point and a high coercive ~ ......
" 2033687 force of a GdTbFe amorphous alloy thin film wherein the GdTbFe amorphous alloy is represented by the following formula:
(GdpTb1p)qFe1q wherein 0.l < q < 0.35, o < p x q < 0.25, o < (l-p) x q <
0.25, and a reading layer with a high Curie point and a low coercive force of a GdNdFe amorphous alloy thin film wherein the GdNdFe amorphous alloy is represented by the following formula:
GdXNdyFe1-x-y wherein 0.l < x < 0.3 and 0 < y < 0.25, which method comprises the steps of applying a magnetic field to the magneto-optic memory medium to develop predetermined data in the reading layer, and subsequently applying both an optical beam and a magnetic field to the magneto-optic memory medium for writing the predetermined data in the recording layer, and simultaneously verifying the data upon said writing on the basis of a Kerr effect of the optical beam caused by the reading layer.
According to the present invention, the coercive force of the reading layer (hereinafter referred to as the first layer) in the magneto-optic memory medium is lower, at around room temperature, than the force of the external magnetic field for writing and the coercive force of the recording layer (hereinafter referred to as the second layer and typically having a force about 200 kOe higher than the first layer). Hence, the direction of magnetization in the first layer quickly becomes the same as that of the external magnetic field without an increase in temperature by the optical beam when the external magnetic field for writing, which is modulated corresponding to recording signals, is applied. As a result, information (predetermined data) is transcribed to the first layer. In this instance, the first layer exhibits a Kerr rotation angle at a level readily detected at a recording (writing) temperature, so that the information transcribed into the first layer is detected on the basis of the Kerr effect of an optical beam applied to the memory medium, specifically to the second layer, for the writing operation. The detected magneto-optic signal is used for verification of the aforesaid information.
Simultaneously with the verification step, the second layer is heated by the optical beam to a temperature near its Curie temperature, and the same information is written when the magnetic field for writing is applied to the second layer, so that the writing and verification steps are conducted simultaneously.
Since the second layer has a higher coercive force, it becomes a stable data-retaining layer at room temperature after the writing step.
Also, the coercive force of the first layer, at around room temperature, is lower than that of the second layer, so that the direction of magnetization of the first layer follows and is stably retained by the second layer as a result of the exchange-coupling force generated between the first and second layers, thereby making the first layer (the reading layer) and the second layer (the recording layer) to be stable record-keeping layers.
According to the recording method for a magneto-optic memory medium of the present invention, the verification of the recorded information can be carried out simultaneously with the recording and/or overwriting steps, thereby increasing the speed of the recording process by more than two times, in comparison with the conventional art.
In the accompanying drawings which illustrate an embodiment of the present invention:
Figure 1 is a cross-sectional view of a magneto-optic memory medium used in the present invention;
Figure 2 is a graphical representation of the temperature dependency of a magneto-optic characteristic measured from the first layer side of the recording layers of the magneto-optic memory medium;
Figure 3 is a graphical representation of the temperature dependency of a magneto-optic characteristic measured from the second layer side of the recording layers of the magneto-optic memory medium;
Figure 4 is a graphical representation of the hysteresis characteristic of the magneto-optic memory medium to an external magnetic field;
Figure 5 is a schematic diagram illustrating a principle of the magneto-optic recording;
Figure 6 is an illustration of a waveform of detected signals on the basis of a Kerr effect of an optical beam upon writing;
Figure 7 is an illustration of a conventional waveform of detected signals on the basis of a Kerr effect of an optical beam upon writing;
Figure 8 is a graphical representation of the compositional dependency of a magneto-optic characteristic of a GdNdFe amorphous alloy film;
Figure 9 is a graphical representation of the compositional dependency of the other magneto-optic characteristic of a GdNdFe amorphous alloy film;
Figure 10 is a graphical representation of the compositional dependency of a magneto-optic characteristic of a TbFeCo amorphous alloy film; and Figure 11 is a graphical representation of the compositional dependency of a magneto-optic characteristic of a DyFeCo amorphous alloy film.
The exchange-coupled magneto-optic memory medium used in the present invention comprises a specific recording layer and a specific reading layer, the layers being laminated on an appropriate substrate. It is usually preferable that the reading layer and the recording layer are formed in this order on a transparent substrate. Preferably the substrate has an intervening first dielectric film of SiN, AlN, ZnS, sio2, SiAlON, AlNGe and the like. Preferably, the recording layer is coated with a second dielectric film.
The recording layer and the reading layer may employ known various amorphous rare earth-transition metal alloy thin films which are applied to an exchange-coupled magneto-optic "' ~A
20~687 memory medium. It is preferable that the reading layer has a Curie temperature greater than that of the underlying recording layer and the recording temperature, upon application of the optical beam. Preferably, the reading layer has a Kerr rotation angle of a readily detectable level at the writing temperature, and has a coercive force, at around room temperature, lower than the magnetic field for writing and the coercive force of the recording layer.
It is particularly preferable that the recording layer is made of GdTbFe amorphous alloy thin film and the reading layer of GdNdFe amorphous alloy thin film.
It is preferable that the recording layer comprises an amorphous alloy thin film represented by the following formula:
(GdpTbl p)qFe1 q wherein p and q satisfy the inequalities 0.1 < q < 0.35, 0 < p x q < 0.25, 0 < (1 - p) x q < 0.25, and the reading layer comprises an amorphous alloy thin film represented by the following formula:
GdXNdyFe1-x-y wherein x and y satisfy the inequalities 0.1 < x < 0.3 and o < y < 0.25.
These amorphous alloy thin films may be formed by sputtering or deposition, for example, the sputtering process using a target of alloys having corresponding compositions or a composite target in an on-chip type, or a multiple-synchronous deposition process using a multiple source.
A suitable thickness of the recording and reading layers is 5,000 ~ or less. Preferably the thickness is in the range of from about 100 to 1000 ~, in consideration of the effect of the exchange-coupling force and recording sensitivity.
The following Examples illustrate the present invention.
EXAMPLES
Referring now to Figure 1, an example of a suitable structure of a magneto-optic memory medium 1 used in the .~
, .. .
present invention will be detailed. The medium 1 comprises a glass substrate 2 and a dielectric layer 3 made of AlN, a reading layer 4 (the first layer) made of GdNdFe, a recording layer 5 (the second layer) made of GdTbFe, and an another dielectric layer 6 made of AlN, those being formed in this order on the substrate 2 to form a double-layered structure by the reading layer 4 and the recording layer 5.
GdNdFe (forming the reading layer 4) is an amorphous alloy having a Gd:Nd:Fe component ratio of 19.0:4.0:77.0% and a thickness of 200 ~. GdTbFe (forming the recording layer 5) is an amorphous alloy having a Gd:Tb:Fe component ratio of 14.0:14.0:72.0% and a thickness of 600 ~.
The temperature dependency of the coercive force Hc and the Kerr rotation angle ek, which are magneto-optic characteristics of the medium 1 constructed as above, were measured from the side of the reading layer 4 (GdNdFe) and the result is shown in Figure 2 wherein the coercive force Hc is shown by the mark o and the Kerr rotation angle ek by the mark . Figure 2 reveals that the reading layer 4 has a low coercive force Hc and is readily magnetized and inverted to have uniform magnetization direction for substantially the whole temperature range when a magnetic field greater than 200 Oe is applied to the reading layer 4. Also, the reading layer 4 has a high Curie temperature, so that the Kerr rotation angle ek is large and kept at a value 50% or more of that at room temperature at about 160C. In a typical magneto-optic recording, the memory layer is raised to a temperature of about 160C by an optical beam for writing, typically a laser beam. Hence, the GdNdFe reading layer 4 is provided with a Kerr rotation angle ek at a level fully and readily detectable at a writing temperature (for example, higher than 0.1 deg), thereby providing a detected signal having a sufficient intensity.
Likewise, the temperature dependency of the coercive force Hc and the Kerr rotation angle ek, which are magneto-optic characteristics of the medium 1, were measured from the side of the recording layer 5 (GdTbFe) and the result is , .
203368~
illustrated in Figure 3 wherein the coercive force Hc is shown by the mark o and the Kerr rotation angle by the mark .
Figure 3 reveals that the recording layer 5 has a coercive force Hc of about 2 kOe at room temperature and is very small at a writing temperature near 160C. This is due to the low Curie temperature of the GdTbFe. Hence, the GdTbFe recording layer 5 is readily magnetized and inverted to follow the direction of the recording magnetic field when the recording magnetic field is applied to the recording layer 5 at the writing temperature, so that the recorded information can be stably retained at around room temperature.
The double-layered structure enables magnetization direction of the reading layer 4 to follow that of the recording layer 5 as a result of the exchange-coupling action.
Figure 4 shows the hysteresis characteristic of the Kerr rotation angle ek measured from the reading layer side with respect to an external magnetic field H. For measurement, the reading layer 4 and the recording layer 5 where initialized by + 2.0 kOe of an external magnetic field at room temperature and subjected to a series of external magnetic field as follows: 0 ~ + 1.0 kOe - 0 Oe ~ - 1.0 kOe ~ 0 kOe, at 60C
of atmosphere. As shown in Figure 4, the values of the Kerr rotation angle ek are constant when the values of the external magnetic field are positive (the same direction as the initialized magnetization), and are inverted when the value of the external magnetic field is about - 0.2 kOe. When the applied external magnetic field is further varied from - 1.0 kOe to 0 kOe, the value of the Kerr rotation angle would again be inverted at about + 0.2 kOe of the external magnetic field if the reading layer 4 is provided without the recording layer 5. But, the value of the Kerr rotation angle is actually inverted again at about - 0.2 kOe and returns to the original value when the hysteresis loop is closed.
The first inversion of the Kerr rotation angle at about - 0.2 kOe corresponds to the above explanation that the reading layer 4 is readily magnetized and inverted in magnetization direction for substantially the whole temperature range due to an applied magnetic field greater than about 200 Oe. Also, the fact that the value of the external magnetic field H is again inverted at about - 0.2 kOe and returned to the original value when the hysteresis loop is closed results from the fact that, when the external field H (causing the reading layer 4 to be inverted) was weakened, an exchange-coupling force between the reading layer 4 and the recording layer 5 caused the reading layer 4 to be inverted again. Since the coercive force Hc of the recording layer 5 is greater than + 1.0 kOe at the measuring temperature of 60C
as shown in Figure 3, the recording layer 5 is not magnetized and inverted by an external magnetic field in the range + 1.0 kOe to - 1.0 kOe but keeps its initialized direction of magnetization. Also, the coercive force Hc of the recording layer 5 is enough to apply an exchange-coupling force to the reading layer 4.
As discussed earlier, the double-layered structure for recording in the medium 1 allows the exchange-coupling force to be produced in order to follow the magnetization direction of the reading layer 4 to that of the recording layer 5.
When a magnetic field 10, which runs in the direction shown by the arrow A in Figure 5 and is modulated corresponding to the predetermined data, is applied to the memory layer of the double-layered structure comprising the reading layer 4 and the recording layer 5, the magnetization direction of the reading layer 4 becomes substantially identical to that of the recording magnetic field 10 prior to an increase in temperature due to the application of a laser beam 7, so that the information (the predetermined data) is transcribed to the reading layer 4. This is because a coercive force of the reading layer 4 is less than the level of the magnetic field 10, as previously mentioned.
Thereafter, when a modulated magnetic field 10, substantially identical in information to the above, and the laser beam 7 (for example, of from about 4.0 to 10 mW output) are applied to the recording layer 5, the temperature of the recording t A
203~687 layer 5 increases to near the Curie temperature, thereby causing a portion 9 subjected to the elevated temperature to have a reduced coercive force and to be magnetized along the direction of the magnetic field 10.
In turn, the reading layer 4 has a Kerr rotation angle ek high enough to be readily detectable at around the writing temperature, so that a detected signal of a sufficient intensity can be obtained by reflection of the laser beam 7 on the basis of its Kerr rotation angle. Since the recorded information is previously transcribed to the reading layer 4 in the same direction as that of the magnetic field, the signals detected from the transcribed information can be applied to verification of recording information.
The detected signals (output by the use of pick-up) in an actual overwriting by use of a floating magnetic head is described hereinafter. The size of the slider of the magnetic head used in the experiment is 6 x 4 mm2 to allow the slider to flow about 5~m above the surface of medium 1. The magnetic head is 0.3 x 0.2 mm2 and 1 mm in length in a single magnetic pole type with 12 turns of 50~m diameter Cu wire, and the driving current is + 0.4 A. The magnetic field generated by the magnetic head was + 200 Oe.
The detected signals upon overwriting by use of the memory medium 1 of the present invention are shown in Figure 6. The film thickness of the dielectric layer 3 is 800 ~ and those of the reading layer 4 and the recording layer 5 are 200 and 600 ~, respectively, as referred to in the explanation of Figure 1, while that of the dielectric layer 6 is 250 ~. The medium 1, before being overwritten, has been written in by use of recording signals of a single frequency of 1.85 MHz. The tester is adapted to jump one track after writing in every track. The recording signal used for overwriting is of a single frequency of 1.0 MHz.
In view of Figure 6, an overwriting detection signal 13 shown by the thick and sold line and having a large amplitude is obtained upon application of the laser beam of 4.0 mW of recording output, and its frequency corresponds to ,~, that (1.0 MHz) of the recording signals. Hence, it was confirmed that it is possible to verify the written data upon overwriting thereof. For reference, the data previously recorded upon the frequency of 1.8S MHz was reproduced before overwriting by the use of a 4.0 mW laser beam, the result of which is shown as a detecting signal 14 in Figure 6.
The detected signals upon overwriting by use of a conventional magneto-optic memory medium is shown in Figure 7, as a comparative example. A magneto-optic memory medium used in this comparison comprises a four-layered structure including a dielectric layer made of AlN, a recording layer made of GdTbFe, a dielectric layer made of AlN and a reflective layer made of Al, laminated in this order on a glass substrate. Also in the comparative example, the medium, before being overwritten, has been written in by recording signals of 1.85 MHz of a single frequency, and recording signals used for overwriting has 1.0 MHz of a single frequency.
In view of Figure 7, since the Kerr rotation angle ek of the above memory layer is small, the overwriting detection signal 15 shown by the thick and solid line and having a rather small amplitude is obtained upon application of the laser beam of 4.0 mW of recording output, and its frequency corresponds to that (1.85 MHz) of a previous recording signal. Hence, it was confirmed that previously recorded data was detected, which is of no use for verification. For reference, the data previously recorded upon the frequency of 1.85 MHz was reproduced by the use of a laser beam of 4.0 mW, the result of which is also shown as a detecting signal 16 in Figure 7.
The recording method for a magneto-optic memory medium of the present invention is not limited in application to the magneto-optic memory medium having the above-mentioned construction. Various examples of magneto-optic memory mediums applicable to the present invention will be detailed hereinafter.
.
A composition of GdNdFe forming the reading layer 4 will be referred to. A compositional dependency of the coercive force Hc of GdNdFe at room temperature is shown in Figure 8, wherein a characteristic when the composition of Nd is fixed at about 4% is shown by the mark o and that with an Nd composition of about 10% is shown by the mark . In the case where the Nd composition is fixed at about 4%, the coercive force of GdNdFe at room temperature is from about 0.4 to 0.9 kOe, but it is restrained to be less than 0.1 kOe at temperatures greater than 100C. By use of a two-layered structure comprising the reading layer 4 and a GdTbFe recording layer 5, the value of the coercive force Hc at room temperature was about 0.15 kOe within the range of from about 17 to 25% Gd, as shown in Figure 2. Also, the Curie temperature of GdNdFe was generally greater than 190C to fully exceed the writing temperature.
The compositional dependency of the Kerr rotation angle of GdNdFe is shown in Figure 9, wherein a characteristic when the composition of Nd is fixed at about 4% is shown by the mark o , that with an Nd composition of about 10% by the mark , and that with an Nd composition of about 21% by the mark ~ . In the case where the Nd composition is fixed at about 4%, the Kerr rotation angle ek exhibits a high value of about 0.4 within the range of from about 17 to 25% Gd.
As a result, when the composition of Nd in the GdNdFe alloy forming the reading layer 4 is fixed at about 4%, the composition of Gd can be set to be from about 17 to 25%.
Any combinations of the reading layer 4 having a film thickness in the range of from 150 to 600 ~, with the recording layer 5 of a film thickness in the range of from 200 to 600 ~, exhibit a substantially identical characteristic to that disclosed in the present example of the invention, thereby enabling the overwriting and the verification steps to be performed simultaneously.
Also, when the characteristics of GdNdFe of the reading layer 4, such as the coercive force Hc, the Kerr rotation angle ek and the Curie temperature are controlled in 203368~
an optimum range, the magneto-optic memory medium for the recording layer 5 may be made of TbFeCo, DyFeCo, GdTbFeCo and the like.
Another suitable magneto-optic memory medium comprises a glass substrate 2, a dielectric layer 3 which is made of AlN and has a film thickness of about 800 ~, a TbFeCo reading layer 4 having a film thickness of about 200 ~, a recording layer 5 which is made of TbFeCo in a different composition ratio to that of the reading layer 4 and has a film thickness of about 600 ~, and a dielectric layer 6 which is made of AlN with a film thickness of about 250 ~, formed in this order of the glass substrate 2. In this case, the Tb:Fe:Co ratio for the reading layer 4 was 10.0:82.0:8.0%, and that of the recording layer 5 was 24.0:68.0:8.0%. The compositional dependency of the coercive force Hc and the Curie temperature Tc of TbFeCo when a composition ratio of Co is fixed at 8.0% is shown in Figure 10, wherein the compositional dependency of the coercive force Hc is shown by the mark o , and that of the Curie temperature Tc by the mark . Referring to Figure 10, the coercive force Hc of the reading layer 4, with a Tb composition of 10.0%, is about 0.4 kOe. Also, the recording layer 5, with a Tb composition of 24.0%, is substantially compensated in composition. It was confirmed that a magneto-optic memory medium constructed as above can simultaneously permit the overwriting and the verification.
The compositional dependency of the coercive force Hc and the Curie temperature Tc of DyFeCo when the composition of Co is fixed at about 19.0% is shown in Figure 11, wherein the compositional dependency of the coercive force Hc is shown by the mark o , and that of the Curie temperature Tc by the mark . Referring to Figure 11, a composition ratio of DyFeCo forming the reading layer 4 and that of DyFeCo forming the recording layer 5 can be selected with an optimum value similarly to the above TbFeCo.
Although the reading layer 4 and the recording layer may be made of the same material having different -20~368~
compositions, the recording layer 5 may be made of GdTbFe, GdTbFeCo, NdDyFeCo and GdDyFe and the like.
A
Claims (11)
1. A recording method for a magneto-optic memory medium of exchange-coupled type having a recording layer with a low Curie point and a high coercive force and a reading layer with a high Curie point and a low coercive force, which comprises the steps of:
applying a magnetic field to the magneto-optic memory medium to develop predetermined data in the reading layer, and subsequently applying both an optical beam and a magnetic field to the magneto-optic memory medium for writing the predetermined data in the recording layer, and simultaneously verifying the data upon said writing on the basis of a Kerr effect of the optical beam caused by the reading layer.
applying a magnetic field to the magneto-optic memory medium to develop predetermined data in the reading layer, and subsequently applying both an optical beam and a magnetic field to the magneto-optic memory medium for writing the predetermined data in the recording layer, and simultaneously verifying the data upon said writing on the basis of a Kerr effect of the optical beam caused by the reading layer.
2. The recording method of claim 1, wherein the recording layer is a GdTbFe amorphous alloy thin film and the reading layer is GdNdFe amorphous alloy thin film.
3. The recording method of claim 1 or 2, wherein each of the recording and reading layers has a thickness in the range of from about 100 to 1000 .ANG..
4. The recording method of claim 1 or 2, wherein the recording layer has a thickness in the range of from about 200 to 600 .ANG. and the reading layer has a thickness in the range of from about 150 to 600 .ANG..
5. The recording method of claim 2, wherein the GdTbFe amorphous alloy is represented by the following formula:
(GdpTb1-p)qFe1-q wherein 0.1 < q < 0.35, 0 < p x q < 0.25, 0 < (1 - p) x q <
0.25, and the GdNdFe amorphous alloy is represented by the following formula:
GdxNdyFe1-x-y wherein 0.1 < x < 0.3 and 0 < y < 0.25.
(GdpTb1-p)qFe1-q wherein 0.1 < q < 0.35, 0 < p x q < 0.25, 0 < (1 - p) x q <
0.25, and the GdNdFe amorphous alloy is represented by the following formula:
GdxNdyFe1-x-y wherein 0.1 < x < 0.3 and 0 < y < 0.25.
6. The recording method of claim 1, 2 or 5, wherein the optical beam is a laser beam.
7. A recording method for a magneto-optic memory medium of exchange-coupled type having a recording layer with a low Curie point and a high coercive force of a GdTbFe amorphous alloy thin film wherein the GdTbFe amorphous alloy is represented by the following formula:
(GdpTb1-p)qFe1-q wherein 0.1 < q < 0.35, 0 < p x q < 0.25, 0 < (1-p) x q <
0.25, and a reading layer with a high Curie point and a low coercive force of a GdNdFe amorphous alloy thin film wherein the GdNdFe amorphous alloy is represented by the following formula:
GdxNdyFe1-x-y wherein 0.1 < x < 0.3 and 0 < y < 0.25, which method comprises the steps of applying a magnetic field to the magneto-optic memory medium to develop predetermined data in the reading layer, and subsequently applying both an optical beam and a magnetic field to the magneto-optic memory medium for writing the predetermined data in the recording layer, and simultaneously verifying the data upon said writing on the basis of a Kerr effect of the optical beam caused by the reading layer.
(GdpTb1-p)qFe1-q wherein 0.1 < q < 0.35, 0 < p x q < 0.25, 0 < (1-p) x q <
0.25, and a reading layer with a high Curie point and a low coercive force of a GdNdFe amorphous alloy thin film wherein the GdNdFe amorphous alloy is represented by the following formula:
GdxNdyFe1-x-y wherein 0.1 < x < 0.3 and 0 < y < 0.25, which method comprises the steps of applying a magnetic field to the magneto-optic memory medium to develop predetermined data in the reading layer, and subsequently applying both an optical beam and a magnetic field to the magneto-optic memory medium for writing the predetermined data in the recording layer, and simultaneously verifying the data upon said writing on the basis of a Kerr effect of the optical beam caused by the reading layer.
8. A recording method of claim 7, in which said optical beam is substantially a constant intensity and a method of said writing the predetermined data in the recording layer is applied by an inversion of the magnetic field.
9. The recording method of claim 7 or 8, wherein each of the recording and reading layers has a thickness in the range of from about 100 to 1000 .ANG..
10. The recording method of claim 7 or 8, wherein the recording layer has a thickness in the range of from about 200 to 600 .ANG. and the reading layer has a thickness in the range of from about 150 to 600 .ANG..
11. The recording method of claim 7 or 8, wherein the optical beam is a laser beam.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2002898A JP2574911B2 (en) | 1990-01-10 | 1990-01-10 | Magneto-optical recording method |
| JP2898/1990 | 1990-01-10 |
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|---|---|
| CA2033687C true CA2033687C (en) | 1995-03-07 |
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| EP (1) | EP0437308B1 (en) |
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| EP0523944A3 (en) * | 1991-07-16 | 1994-02-16 | Canon Kk | Magneto optical recording medium and method |
| JPH0536141A (en) * | 1991-07-30 | 1993-02-12 | Sony Corp | Magneto-optical recorder |
| JPH05144114A (en) * | 1991-11-19 | 1993-06-11 | Canon Inc | Magneto-optical recorder |
| US5485433A (en) * | 1991-12-19 | 1996-01-16 | Canon Kabushiki Kaisha | Information recording method and apparatus for determining whether recording has been correctly performed |
| EP0559391B1 (en) * | 1992-03-03 | 1998-06-03 | Canon Kabushiki Kaisha | Magnetooptical recording/reproducing method and apparatus |
| US5434844A (en) * | 1992-04-10 | 1995-07-18 | Hitachi, Ltd. | Magneto-optical recording media and magneto-optical recording device using the same |
| DE69331924T2 (en) * | 1992-08-28 | 2002-10-10 | Canon Kk | Magneto-optical recording medium and information recording and reproducing method therewith |
| USRE38501E1 (en) * | 1992-08-28 | 2004-04-20 | Canon Kabushiki Kaisha | Magnetooptical recording medium and information recording and reproducing methods using the recording medium |
| DE4230580C1 (en) * | 1992-09-12 | 1993-08-05 | Rockwell Golde Gmbh, 6000 Frankfurt, De | |
| JPH07254175A (en) * | 1994-03-16 | 1995-10-03 | Canon Inc | Magneto-optical recording medium and method for recording and reproducing information with same medium |
| JP2766198B2 (en) * | 1994-09-05 | 1998-06-18 | 富士通株式会社 | Magneto-optical recording medium |
| US5644555A (en) * | 1995-01-19 | 1997-07-01 | International Business Machines Corporation | Multiple data surface magneto-optical data storage system |
| US5798993A (en) * | 1995-05-29 | 1998-08-25 | Nec Corporation | System and method for simultaneously verifying optical data writing and optical data writing medium for use therein |
| US6724674B2 (en) * | 2000-11-08 | 2004-04-20 | International Business Machines Corporation | Memory storage device with heating element |
| US6603678B2 (en) * | 2001-01-11 | 2003-08-05 | Hewlett-Packard Development Company, L.P. | Thermally-assisted switching of magnetic memory elements |
| US20030198146A1 (en) * | 2002-04-18 | 2003-10-23 | Seagate Technology Llc | Heat assisted magnetic recording head with multilayer electromagnetic radiation emission structure |
| US6839271B1 (en) | 2003-10-15 | 2005-01-04 | Hewlett-Packard Development Company, L.P. | Magnetic memory device |
| US7522446B2 (en) * | 2003-10-31 | 2009-04-21 | Samsung Electronics Co., Ltd. | Heating MRAM cells to ease state switching |
| US7158346B2 (en) * | 2003-12-23 | 2007-01-02 | Seagate Technology Llc | Heat assisted magnetic recording film including superparamagnetic nanoparticles dispersed in an antiferromagnetic or ferrimagnetic matrix |
| US6956271B2 (en) * | 2004-02-11 | 2005-10-18 | Hewlett-Packard Development Company, L.P. | Switching of soft reference layers of magnetic memory devices |
| US7193889B2 (en) * | 2004-02-11 | 2007-03-20 | Hewlett-Packard Development Company, Lp. | Switching of MRAM devices having soft magnetic reference layers |
| US7102921B2 (en) * | 2004-05-11 | 2006-09-05 | Hewlett-Packard Development Company, L.P. | Magnetic memory device |
| US7397074B2 (en) | 2005-01-12 | 2008-07-08 | Samsung Electronics Co., Ltd. | RF field heated diodes for providing thermally assisted switching to magnetic memory elements |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60117436A (en) * | 1983-11-29 | 1985-06-24 | Sharp Corp | Magnetooptic storage element |
| JPS6122452A (en) * | 1984-07-09 | 1986-01-31 | Kokusai Denshin Denwa Co Ltd <Kdd> | Photomagnetic recording medium |
| DE3584945D1 (en) * | 1984-10-30 | 1992-01-30 | Brother Ind Ltd | MAGNETOOPTIC STORAGE MEDIUM AND DEVICE FOR WRITING ON AND READING FROM THE MEDIUM. |
| US4794560A (en) * | 1985-09-30 | 1988-12-27 | International Business Machines Corporation | Eraseable self biasing thermal magneto-optic medium |
| US4871614A (en) * | 1986-07-09 | 1989-10-03 | Canon Kabushiki Kaisha | Opto-magnetic recording medium having three exchange-coupled magnetic layers |
| JPS63157340A (en) * | 1986-12-20 | 1988-06-30 | Fujitsu Ltd | Magneto-optical recording/reproducing device |
| US5051970A (en) * | 1987-05-08 | 1991-09-24 | Nippon Telegraph And Telephone Corporation | Magneto-optic recording system with overwrite capability |
| JP2680586B2 (en) * | 1987-11-26 | 1997-11-19 | シャープ株式会社 | Magneto-optical storage medium |
| EP0330394B1 (en) * | 1988-02-22 | 1996-07-17 | Canon Kabushiki Kaisha | Two-layered type opto-magnetic recording medium having low-coercive force layer containing Gd and at least one of Tb and Dy |
-
1990
- 1990-01-10 JP JP2002898A patent/JP2574911B2/en not_active Expired - Fee Related
-
1991
- 1991-01-02 EP EP91300028A patent/EP0437308B1/en not_active Expired - Lifetime
- 1991-01-02 DE DE69111622T patent/DE69111622T2/en not_active Expired - Fee Related
- 1991-01-07 CA CA002033687A patent/CA2033687C/en not_active Expired - Fee Related
- 1991-01-07 US US07/638,076 patent/US5224068A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0437308A3 (en) | 1992-04-15 |
| DE69111622D1 (en) | 1995-09-07 |
| DE69111622T2 (en) | 1996-01-18 |
| EP0437308A2 (en) | 1991-07-17 |
| JP2574911B2 (en) | 1997-01-22 |
| EP0437308B1 (en) | 1995-08-02 |
| US5224068A (en) | 1993-06-29 |
| JPH03207040A (en) | 1991-09-10 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKLA | Lapsed |