JP2997493B2 - Magneto-optical recording medium - Google Patents

Description

The present invention relates to a rewritable magneto-optical medium, and more particularly to a two-layer rare earth-transition metal (R) coupled via at least exchange force. -T) a technique for controlling the exchange force of a magneto-optical medium having a film.

(Prior art) Heating by irradiating a laser beam, lowering the coercive force of the heating section, and aligning the magnetization direction of the portion where the coercive force is reduced with the direction of the external magnetic field to record or erase information,
2. Description of the Related Art A magneto-optical recording medium that reproduces information using the magneto-optical Kerr effect according to the direction of magnetization has been put to practical use as a rewritable optical disk memory medium. In the recording layer of the magneto-optical medium, a perpendicular magnetization film can be easily obtained, the stability of the minute reversal domain is good, recording and erasing can be easily performed with a practical semiconductor laser, and there is no grain boundary noise. And an amorphous RT film. However, it is difficult to achieve both high recording sensitivity and high reproduction signal intensity ratio with a single layer. Therefore, although the sensitivity is high, the Kerr rotation angle is relatively small.
A medium has been proposed in which a film (for example, a Tb-Fe film) is used as a recording layer, and an RT film (for example, a Gd-Fe film) having a relatively large Kerr rotation angle and low sensitivity is laminated via an exchange force. I have. In recent years, a large number of exchange-coupled multilayer media have been proposed for the purpose of providing a light modulation overwrite function which is difficult to realize in a single-layer RT media, and as a next-generation magneto-optical medium. Its development is expected.

When performing the recording / reproducing / erasing operation using the exchange coupling medium, this is particularly the case where the light modulation overwrite function is to be realized, but the upper and lower R-coupled via the exchange force are used. It is extremely important to control the exchange force (H _ex g) acting between the T membranes.

H _ex g indicates the interface domain wall energy density E _wB , and the magnetization of each layer
Assuming that the thickness of each layer of M _s1 and M _s2 is d ₁ and d ₂ , The conversion power works, and the layer 2 E _wB , M _s1 , M
_s2, the optimal design of d _1, d ₂ is important.

In the light modulation overwrite method using the exchange-coupling two-layer film, near the Curie point of the recording layer, H _ex g ₁ (assuming the recording layer is layer 1) is larger than the recording layer coercive force H _c1 by the exchange force. The magnetization of the recording layer (strictly speaking, sub-lattice magnetization) is aligned with the direction of the magnetization of the auxiliary layer (strictly speaking, sub-lattice magnetization), and the normal temperature (memory holding temperature) and the reproducing temperature (at the time of reproducing laser beam irradiation). in film temperature), at room temperature it and H _ex g ₁ is small recording bits than H _c1 can exist stably H _ex g
₂ (assuming that the auxiliary layer is layer 2) is smaller than H _c2 and it is an essential condition that the auxiliary layer is oriented in a certain direction after the application of the initialization magnetic field. It is important to control the film temperature. In the conventional exchange-coupled multilayer film, consideration for H _ex g is not always sufficient.

Although there is a method using the in-plane magnetization intermediate layer and a process-side approach, the former may complicate the media layer structure and reduce the productivity of the media, and the latter accurately monitors the state of the interface during manufacturing. If it is not possible, the yield will not be improved.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned problems of the prior art, and the layer structure may be basically a simple exchange mixed two-layer film. Without taking advantage of the fact that the exchange force at the interface between dissimilar transition metals is simply smaller than the exchange force at the interface between transition metals, It is an object of the present invention to provide a magneto-optical recording medium having excellent stability of recording bits at room temperature or reproduction temperature and good stability of magnetization of the auxiliary layer, particularly by lowering the value of

[Constitution of the Invention] (Means for Solving the Problems) The present invention provides a magneto-optical device comprising a stack of a plurality of amorphous rare earth-transition metal alloy thin films having an easy axis of magnetization in a direction perpendicular to the film surface. In a recording medium, at least one of the plurality of stacked layers has upper and lower layers connected to each other via exchange force in a range where the interface domain wall energy between the layers is 3 erg / cm ² or less, and constitutes the upper and lower layers. A magneto-optical recording medium characterized in that the main component of the transition metal element in one of the two thin films is Fe, and the main component of the transition metal element in the other thin film is Co. Here, the main component is generally expressed by RxT _100-x (x: at%) (when an additional element other than R and T is contained, or R is a rare earth element in addition to a rare earth element. May be used) T
If the component is further expressed as (Fe _100-y Co _y ) {y: at%}, the main component of Fe means y50at%, and the main component of Co means y50at%. When only Fe and Co are extracted regardless of the type of R, additive element, and the like, the T component means the main component in the composition of the T component.

(Action) The present invention generally relates to the same type of T element (Fe main component-Fe main component,
Or oversized E _wB when is exchange-coupled two-layered film of Co main component -Co ingredient) can be reduced by using a two-layered film of a heterologous T elements. For this reason, the magnetization of the recording layer and the auxiliary layer at room temperature or reproduction temperature can be kept stable, and the reliability of the memory can be improved. For example, as a typical example, M _s1 = 100ewu / cc, d ₁ = 100 nm at normal temperature
In the case of using the recording layer, H _ex g ₁ Because the case of using the exchange coupling medium consisting of allogeneic T element is E _wB 5erg / cm ² is 2.
5koe reached, while becomes H _c1 syngeneic to or greater, the use of the exchange coupling medium made of different T element
Since E _wB can be reduced to about ² erg / cm ² b, H _ex g ₁ becomes about ₁ koe, which is smaller than H _c1, and the stability of the memory bit is improved. Further H _ex g ₁ except that improves the productivity of the medium can be small and d ₁ by reducing the E _wB is inversely proportional to d _1, it is also advantageous to perform the proper design of the car enhancement film structure.

(Example) Hereinafter, a magneto-optical recording medium of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a magneto-optical recording medium according to an embodiment of the present invention, wherein 1 is a recording layer, 2 is an interface on which an exchange force can act, 3 is an auxiliary layer formed by exchange coupling to 1, 4 , 5 is a protective layer,
6 is a substrate. The medium of FIG. 1 is formed, for example, by the following method. The glass substrate 6 was set in the sputtering apparatus, and the film forming chamber was evacuated to about 10 ^-7 Torr, and then Ar gas was discharged.
After introducing 0 sccm and setting the film forming chamber pressure to 5 × 10 ⁻³ Torr, first, an RF power of 1 kW was applied to a magnetron sputtering source equipped with a Si ₃ N ₄ target to form a protective film 5, and then, for example, Tb ₂₀ DC power is applied to the Fe ₈₀ alloy target to form a recording layer 1 of 100 nm. Continuously, DC power is applied to the Tb ₂₇ (Fe ₂₀ Co ₈₀ ) ₇₃ alloy target to form an auxiliary layer 3 of 100 nm and Si ₃ again. RF power is applied to the N ₄ target to form the protective layer 4. The composition of the RT film slightly shifted to the R-poor side from the alloy target composition, and the composition of the recording layer of the medium thus obtained was Tb ₁₈ Fe ₈₂ , while the composition of the auxiliary layer was Tb ₁₈ Fe ₈₂ .
₂₅ (Fe ₂₀ Co ₈₀ ) ₇₅ . The first thus obtained
When the medium shown in the figure was measured at room temperature by a VSM, sweeping of an external magnetic field _Hex of ± 10 kOe yielded a typical conversion coupling bilayer MH loop as shown in FIG. 2 (a). In this case, the recording layer is an anti-parallel type conversion coupling film which is Tb ₁₈ Fe ₈₂ and TM-rich sense, and the auxiliary layer is Tb ₂₅ (Fe ₂₀ Co ₈₀ ) 75 and RE-rich sense. In (a), an interface domain wall is formed in the states of F, A, C, and D, and no interface domain wall is formed in the states of B and E. The transition from A to B or D to E occurs in the recording layer Tb ₁₈ Fe ₈₂
The characteristics of a single recording layer are M
A → B or D because _s1 = 125ewu / cc, H _c1 = 2koe
With the transition of → E, M rises or falls by 125ewu / cc, the transition magnetic field is 1.2 kOe at H _c1 −H _ex g ₁ , and the transition of B → C or E → F is accompanied by the inversion of the auxiliary layer. The characteristics of the single auxiliary layer are M _s2 = 100ewu / cc and H _c2 = 5kOe.
In the transition from → C or E → F, M increased or decreased by 100ewu / cc, and the transition magnetic field was H _c2 + H _ex g ₂ and 6 kOe. As a more accurate derivation method of H _ex g ₁ , there is a method in which H _ex is reduced from the B state in FIG. 2 (a) to draw a loop, and the loop obtained in this way is shown in FIG. )Pointing out toungue. In FIG. 2 (b), the transition field of A → B is H _c1 -H _ex g _1, the transition field of the G → F is H _c1 + H _ex
g ₁ , half of the difference between the two transition magnetic fields gives H _ex g _1, which is given by M _s1 and the film thickness d ₁ obtained from the loop of FIG. 2A or the loop of the recording layer single layer. E _wB is calculated by dividing by twice the product of FIG. 3 is a diagram in which E _wB is derived and plotted by the above-mentioned method, with some y in the auxiliary layer Tb ₂₅ (Fe _100-y Co _y ). When an auxiliary layer mainly composed of Fe is laminated on a recording layer mainly composed of Fe, E _wB > 3 erg / cm ² and H _ex g ₁ >
1.2 kOe compared to the case using Co-based auxiliary layer E
_wB 3erg / cm ² , H _ex g ₁ <1.2 kOe, and more typically, when an auxiliary layer of Tb ₂₅ Fe ₇₅ is used as a Fe—Fe combination, E ^wB = 7 erg / cm ² and H _ex g ₁ = 2.8 kOe, which exceeds H _c1 , whereas when an auxiliary layer of Tb ₂₅ Fe ₇₅ is used as a Fe—Co combination, H _ex g ₁ = 0.6 at E _wB = 1.5 erg / cm ² kOe
In lower 1.4kOe than H _c1, for example, the memory bits even when applying a magnetic field of 1kOe externally with respect to the recording layer is so stored seen that reliability is improved.

In the above example, the Tb ₁₈ Fe ₈₂ recording layer and Tb ₂₅ (Fe _100-y Co _y )
Although an example in which the auxiliary layer is exchange-coupled has been described, the present invention is not limited to the method of selecting the R element. As R, Gd, Dy, Nd, Ho, etc. can be used in addition to Tb. Al, Ti, Cr, An
Etc. may be contained. The medium may be composed of three or more layers other than two layers. In such a case, the medium has at least one exchange-coupling interface, and at least one exchange-coupling interface above and below at least one exchange-coupling interface. It suffices that one of the main components of T in the film is Fe and the other is Co.

[Effect of the Invention] By using the magneto-optical recording medium of the present invention, the interface domain wall energy density of the exchange-coupling multilayer medium can be controlled to a desired value, so that the stability of 6 bits at the memory holding temperature and the memory reproducing temperature can be improved. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of a magneto-optical recording medium of the present invention,
FIG. 2 and FIG. 3 are diagrams showing characteristics of one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Recording layer, 2 ... Interface, 3 ... Auxiliary layer, 4,5 ... Protective layer, 6 ... Substrate

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yumi Mizusawa 70, Yanagicho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Yanagicho Plant (56) References JP-A-61-48149 (JP, A) JP-A-3 -1556752 (JP, A) JP-A-3-162742 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 11/10

Claims (1)

(57) [Claims] 1. A magneto-optical recording medium comprising a plurality of layers of an amorphous rare earth-transition metal alloy thin film having an easy axis of magnetization in a direction perpendicular to the film surface, wherein at least one interface of the plurality of layers is laminated. The upper and lower layers of the interface are coupled via an exchange force in a range where the interface domain wall energy between the layers is 3 erg / cm ² or less, and the transition metal element in one of the two thin films constituting the upper and lower layers Wherein the main component is Fe, and the main component of the transition metal element in the other thin film is Co.