JP3128095B2 - Recording / playback method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing method in the field of rewritable nonvolatile storage of information such as an optical disk and a magnetic disk.

[0002]

2. Description of the Related Art In the field of information file storage, magnetic disks and optical disks are used as rewritable and high-density storage systems. Although the recording density of each of these is increasing year by year, it is difficult to secure the SN at the time of reproduction, and it is approaching its limit. In addition, in these methods, when copying the recorded information of one medium to another medium, it is necessary to read the information one-dimensionally and write it to the copy destination medium. The development of a method to do this was desired.

[0003]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above problems, and it is an object of the present invention to provide a recording / reproducing method exhibiting a high SN even in high-density recording. It aims to provide technology that enables

[0004]

To achieve the above object, according to an aspect of the present invention is antiferromagnetic - Ji raw ferromagnetic transition, the heating time and cooling
The <br/> magnetic material exhibiting hysteresis, wherein the transition temperature is different in却時, lower than the temperature t ₂ causing the transition upon heating
Ku, and higher than the temperature t ₁ to produce the transition upon cooling
While maintaining the temperature t _b, local temperature t of the magnetic material
Heat is applied to _two or more portions to generate ferromagnetism or antiferromagnetism in the heated portion , and information is recorded. Thereafter, the amount of magnetization of the heated portion, a change in magnetization, or a state amount such as a direction of magnetization, etc. SUMMARY OF THE INVENTION The gist of the present invention is a storage / reproduction method characterized in that information is reproduced by detecting the information. Further, the present invention locally heats the magnetic material while maintaining the first magnetic material that causes an antiferromagnetic-ferromagnetic transition in a temperature range in which the transition occurs, so that the heated portion is ferromagnetic or ferromagnetic. After recording information by causing antiferromagnetism,
The second magnetic material is brought into close contact in the temperature range to transfer information from the first magnetic material on which the information is recorded to the second magnetic material, and the second magnetic material is brought into close contact with and detached from the second magnetic material. The gist of the invention is a recording / reproducing method characterized in that information is reproduced by detecting a state quantity such as a magnetization amount, a magnetization change, or a magnetization direction from a material.

[0005]

According to the present invention, recording and reproduction are performed using the hysteresis phenomenon of magnetization, so that high SN reproduction and multi-value recording at a high recording density can be realized.

First, the principle of the recording / reproducing method of the present invention will be described. Antiferromagnetic-ferromagnetic transition is FeRh alloy, HfTa
Occurs in Fe ₂ , SoTiFe ₂ , Co (FeAl) ₂ -based intermetallic compounds, Mn ₃ Pt ordered alloys, etc., and rapidly changes from antiferromagnetic to ferromagnetic or from ferromagnetic to antiferromagnetic at a certain temperature It is a phenomenon that does. This transition generally shows a hysteresis phenomenon, and the transition temperature differs between heating and cooling. The present invention realizes a new recording / reproducing method using this hysteresis phenomenon.

FIG. 1 schematically shows an example of the change in magnetization with respect to the temperature of the antiferromagnetic-ferromagnetic transition. First, at a low temperature, there is almost no magnetization due to the antiferromagnetic state, but at the temperature of t ₂ , magnetization is generated due to transition to ferromagnetism. Once heated to at least t ₂ , transition from ferromagnetic to antiferromagnetic occurs at a temperature t ₁ lower than t ₂ , showing hysteresis with respect to temperature. Here, the antiferromagnetic - a material showing ferromagnetic transition, held at environmental temperature t _b of the indicated area of hysteresis, heating the portion to be recorded t ₂ or more, returning after being heated once to t _b Area only M ₂
Has the magnetization of If this temperature state of t _b is maintained, the recording bit of the magnetization M ₂ can be maintained. Temperature t _b , or the start and end temperature t _{2 of} the hysteresis,
t ₁ depends on the alloy system, additive element, pressure, applied magnetic field, etc.
Can be easily controlled. Further, if t ₁ is set to be equal to or lower than the room temperature and t ₂ is set to be equal to or higher than the room temperature, it is possible to hold the record at the normal temperature without specially setting the bias temperature. When erasing information, if the temperature is changed from the state t _b to a temperature equal to or lower than t ₁ , the recording bit is erased because the entire magnetization becomes M ₁ . Further, even if the heating is performed for t ₂ or more, the entirety becomes M ₂ in the same manner, and erasing is possible. The major difference here from the recording state of conventional magnetic disks and optical disks is that the recorded area and the non-recorded area
That is, the state of the presence or absence of the magnetization itself is maintained. Therefore, when reproduction is performed using a magnetic head or a magnetoresistive element, the noise level can be extremely reduced, and reproduction can be performed even with small bits. A recording medium in a magnetic disk or an optical disk has a certain magnetization, and the direction of this magnetization is changed in a vertical direction or a horizontal direction of the medium to record bits.

FIG. 2 shows a recording state of a medium in a conventional magnetic disk or optical disk. FIG. 2A shows a state of recording bits in magnetic recording. Here, the arrow indicates the direction of magnetization. (B) shows the state of recording bits in optical recording. For this reason, a boundary portion between a recording bit and a non-recording bit or a region where recording is insufficient has magnetization information in a direction opposite to the direction of magnetization of the bit to be recorded, and the magnetic head and the optical head. In the case of reproduction by a magnetic sensor such as a magnetic head, since the bit information is detected as noise information opposite to the direct bit information, there is an essential problem of causing a reduction in the SN ratio. On the other hand, in the present invention, since the region other than the recording bit has no magnetization itself or only the recording bit has no magnetization, noise from other than the bit is essentially eliminated in reproduction by the magnetic sensor. Does not exist,
Even if recording is performed at a high recording density, high SN reproduction can be realized.

FIGS. 3A and 3B show an example of multi-level recording by applying a magnetic field according to the present invention, wherein FIG. 3A is a diagram showing a recording state viewed from above, and FIG. (C) shows the state of the waveform reproduced by the optical head. If a magnetic field is applied during writing in this manner, the direction of magnetization of the recording bit is fixed, so that the recorded information can be stored and stored as information on the direction of magnetization as well as the presence or absence of magnetization. Therefore, it can also be used as a multi-valued information recording method. Additional advantages include the following. That is, since the change in magnetization due to the antiferromagnetic-ferromagnetic transition is very large as compared with the amount of recorded magnetization in a conventional magnetic disk or optical disk medium, recorded information can be easily transferred to another magnetic material. For example, a magnetic disk medium has a residual magnetization of 2500 to 10000 G, and a magneto-optical disk medium has a residual magnetization of 2000 G or less.
About 140 for FeRh, an antiferromagnetic-ferromagnetic transition material
00G magnetization occurs. In the recording method of the present invention, T
By forming a two-layer structure in which an amorphous magnetic thin film such as bFe or GdTbFe or a garnet magnetic thin film such as YGdGaFeO is adhered, recorded information of an antiferromagnetic-ferromagnetic transition material can be copied two-dimensionally and collectively. , Which makes it difficult to copy information.

[0010]

Next, an embodiment of the present invention will be described. [Example 1] An Fe _0.5 Rh _0.5 alloy thin film having a thickness of about 1000 ° was formed on a glass disk substrate by sputtering.
FIG. 4 shows the relationship between the temperature and the magnetization of the Fe _0.5 Rh _0.5 thin film. The horizontal axis shows the temperature, and the vertical axis shows the state of the magnetization. As shown in FIG. 4, the temperature change of the magnetization of the thin film is 80 at t _2.
° C, t ₁ is −15 ° C., magnetization M _{2 in} a ferromagnetic state is about 1000
G shows a hysteresis of about 12 G of magnetization M ₁ in the antiferromagnetic region. The temperature dependence of the force-effect by the semiconductor laser having a wavelength of 833 nm also showed hysteresis as shown in FIG. FIG. 5 shows the relationship between the temperature, force, and rotation angle (wavelength: 833 nm) of the Fe _0.5 Rh _0.5 thin film. While maintaining the thin film at room temperature, the semiconductor laser was heated at 60 mW at an interval of 1 μm in the circumferential direction by an optical head of a semiconductor laser, and was reproduced at 15 mW. Also,
Erasing was possible by continuously irradiating with 15 mW.

Example 2 A thin film of Hf _0.8 Ta _0.2 Fe ₂ was formed to a thickness of 3000 ° on glass. The temperature change of the magnetization was as shown in FIG. Unlike the first embodiment, tb = −
When heating is locally performed while maintaining the temperature at 90 ° C., the magnetization of the heated region disappears. While the atmosphere temperature was kept at -90 ° C., heating was performed with an Ar laser at intervals of 10 μm and reproduction was performed with an optical head. As a result, reproduction was possible.

[Embodiment 3] Fe _0.52 Rh _0.48 alloy thin film 3
000 ° was formed on a glass disk substrate in the same manner as in Example 1. The change in magnetization temperature is shown in FIG. This thin film was recorded at 80 mW with a semiconductor laser while changing the polarity at 5 kHz with a 600 G magnetic field perpendicular to the film surface at an ambient temperature of 60 ° C. FIG. 8 shows a waveform reproduced from the same with the head of 10 mW. The ternary signal of information from the bit whose recording magnetization is directed to the lower part of the film surface, the reproduction information from the hit which is directed to the upper part of the film surface, and the information from the non-recording area are clearly recognized, and the multi-valued information recording is performed. I realized it. The bias magnetic field can be applied in the in-plane direction of the film.

[Embodiment 4] Recording combined with the second layer,
An example of transfer and reproduction will be described. FIG. 9 shows a state of transfer, in which 1 is a glass substrate, 2 is GdTbFe
Co thin film, 3 a FeRh thin film, 4 a glass substrate, 5 a recording bit. For the thin film used in Example 3, bits were recorded with an 80 mW laser beam while applying a magnetic field of 5 kOe in a direction perpendicular to the film surface in an atmosphere of 60 ° C. in the same manner. A region having magnetization in the vertical direction only in the heated portion is formed and held. After this, FeRh
Second magnetic thin film Gd _11.7 Tb _8.6 Fe _71.1 Co _8.6 (thickness: 1) magnetized in a direction opposite to the magnetic field when recording on the thin film
(500 °) was brought into close contact with the FeRh thin film. This Gd _11.7 Tb _8.6 Fe _71.1 Co _8.6 thin film is
It has a great effect and has perpendicular magnetic anisotropy, and the temperature of the magnetic characteristics shown in FIG. 10 is generated. In FIG., H _c is the holding force, M _s denotes the saturation magnetization. At an ambient temperature of 60 ° C., the coercive force is about 400 Oe, and only the bit information is Gd due to the leakage magnetic field from the recording bit in the magnetization state M _{2 in} FIG.
Transferred to _11.7 Tb _8.6 Fe _71.1 Co _8.6 thin film. Reproduction was possible using the optical head from the direction of the second layer (from above in FIG. 9) in the state of close contact, and detection was possible with higher sensitivity than reproduction of bits of only the first layer. Gd _11.7 Tb _8.6 F
The coercivity of the e _71.1 Co _8.6 thin film is further increased at room temperature, so that the information is further stabilized and can be stored. The recorded state can be reproduced even with the second layer alone. Similarly, first, a picture or a character is recorded on the FeRh thin film with a heat pen, and Gd
These were also transferred by bringing the TbFeCo thin film into close contact. As described above, after recording on the first layer,
By bringing the second layer into close contact, the reproduction sensitivity is improved. It has been proved that an effect that any two-dimensional information can be transferred at once by using the information of the first layer as an original appears.

[0014]

As described above, according to the present invention, the antiferromagnetic - ferromagnetic transition Ji live, the transition temperature is different at the time of cooling and during heating
When a magnetic material showing a hysteresis phenomenon is heated,
Lower than the temperature t ₂ which produces and raw said transition upon cooling
While maintaining the high temperature t _b than cunning temperature t _1, locally heated to a temperature t ₂ than the magnetic material, the heating portion
And allowed rise to ferromagnetic or antiferromagnetic to perform recording of information, then the magnetization of the heated portion, by using the recording and reproducing method of the present invention to detect the state quantity such as the direction of magnetization change or magnetization, high High SN reproduction and multi-level recording with a high recording density are possible, and two-dimensional batch copying of information is also possible.

[Brief description of the drawings]

FIG. 1 shows an example of a temperature change of magnetization of an antiferromagnetic-ferromagnetic transition magnetic material.

FIG. 2 shows a recording state of a medium in a conventional magnetic disk or optical disk.

FIG. 3 shows an example of multilevel recording by magnetic field application writing according to the present invention.

FIG. 4 shows a temperature-magnetization relationship of the Fe _0.5 Rh _0.5 thin film used in Example 1.

FIG. 5 shows a relationship between temperature, force, and rotation angle (wavelength: 833 nm) of the Fe _0.5 Rh _0.5 thin film used in Example 1.

FIG. 6 shows a temperature-magnetization relationship of the Hf _0.8 Ta _0.2 Fe ₂ thin film used in Example 2.

FIG. 7 shows a temperature-magnetization relationship of the Fe _0.52 Rh _0.48 thin film used in Example 3.

FIG. 8 shows a reproduced waveform in the third embodiment.

FIG. 9 shows a transfer method according to a fourth embodiment.

FIG. 10 shows a temperature change of magnetic characteristics of a GdTbFeCo thin film in Example 4.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 glass substrate 2 GdTbFeCo thin film 3 FeRh thin film 4 glass substrate 5 recording bit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-179902 (JP, A) JP-A-57-201346 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/02 H01F 13/00

Claims (4)

(57) [Claims] 1. A antiferromagnetic - Ji raw ferromagnetic transition, the time of heating
During cooling, the transition temperatures show different hysteresis phenomena.
The magnetic material is heated from the temperature t ₂ at which the transition occurs when heated.
Low and high than the temperature t ₁ to produce the transition upon cooling
While maintaining the stomach temperature t _b, local temperature of the magnetic material
was heated to t ₂ or more, the the heating portion brought rise to ferromagnetic or antiferromagnetic performs recording of information, then the magnetization amount of the heating <br/> portion, the state quantities such as the direction of magnetization change or magnetization And reproducing the information by detecting the information. Wherein said magnetic material temperature t ₂ or more or a temperature
By the t ₁ below, storing and reproducing method according to claim 1, wherein the erasing of the recorded information. 3. A method according to claim 1 , wherein a constant bias magnetic field or a periodically changing alternating magnetic field is applied to a surface of said magnetic material in a perpendicular direction or an in-plane direction when recording information. Item 2. The recording / reproducing method according to Item 1. 4. The method according to claim 1, wherein the magnetic material is locally heated while maintaining the first magnetic material causing an antiferromagnetic-ferromagnetic transition in a temperature range in which the transition occurs. After recording information by causing antiferromagnetism, a second magnetic material is brought into close contact with the temperature range to transfer the information from the first magnetic material on which the information is recorded to the second magnetic material. A recording / reproducing method, wherein the information is reproduced by detecting the amount of magnetization from the second magnetic material, the change in magnetization, or the state amount such as the direction of magnetization in the adhered state and the detached state.