JPH03230342A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a magneto-optical recording medium having low Curie temp., large squareness ratio and large transverse Kerr effect by forming a magnetization film comprising iron, platinum and inevitable impurities for the magneto-optical recording medium and specifying the amt. of platinum incorporated into the layer to <=40 atomic %. CONSTITUTION:A magnetization film 2 is formed on a substrate 1 to constitute the magneto-optical recording medium. The substrate 1 consists of such a material having the coefft. of thermal expansion of <=120X10<-7>/ deg.C which is lower than that of the magnetization film 2. The magnetization film 2 consists of iron, platinum and inevitable impurities with the amt. of platinum specified to <=40 atomic %. Thereby, the obtd. magneto-optical recording medium has low Curie temp., large squareness ratio and large transverse Kerr effect.

Description

[Detailed description of the invention] [Industrial application field] The present invention records information using the magneto-optical effect.

The present invention relates to a magneto-optical recording medium used in a magneto-optical recording/reproducing device that performs erasing and reproduction.

[Prior art]

As information becomes more sophisticated, information file devices are required to have larger capacities and higher densities, and magneto-optical recording and reproducing devices are attracting attention as rewritable magnetic recording and reproducing devices.

Conventional magneto-optical recording and reproducing devices use a perpendicularly magnetized film as the magneto-optical recording medium, so the magnetic film itself requires a high coercive force to overcome the large demagnetizing field associated with magnetization, and the recording and reproducing device itself also uses a perpendicularly magnetized film. A strong magnetic field generation source is required that generates a magnetic field in the direction perpendicular to the film surface.Furthermore, in order to convert the amount of rotation of the polarization plane of the reflected light due to the Kerr effect into a change in light intensity, a polarization beam substrate + 'A wavelength is required. Polarization optical components such as plates are required, which complicates the optical system, making it difficult to reduce the size and weight of the device, and making it difficult to increase access and data transfer speeds.

As a countermeasure to this problem, the present inventor used an in-plane magnetized film in a magneto-optical recording medium, recorded information in the in-plane direction of the magnetized film according to the direction or magnitude of magnetization, and recorded information on the magneto-optical recording medium substantially perpendicular to the direction of magnetization. Information is recorded based on the light intensity of the reflected light obtained depending on the direction or magnitude of magnetization of the magneto-optical recording medium.

We have already proposed a magneto-optical recording and reproducing method (Japanese Patent Application Laid-Open No. 63-44851, Patent Application No. 19828-1983).
No. 7).

This method does not require a high coercive force in the magneto-optical recording medium itself, has a wide range of material selection for the magnetization film, can use materials with high output and high reliability, and has high Ei flux efficiency. The use of ring type magnetism makes it easy to configure the magnetic field generation source, and by presenting recorded information directly as a change in light intensity, the optical system can be simplified and high reproduction output can be obtained. There is.

[Problems to be Solved by the Invention] By the way, one of the final functions that should be provided as a magneto-optical recording medium for a magneto-optical recording and reproducing method as described in n71 proposed by the present inventor (in the direction of H). When light is incident in a direction substantially perpendicular to the direction, the intensity of the reflected light changes depending on the direction or magnitude of magnetization, which is the so-called lateral force effect, which is observed. Materials 4 include Fe, Co, and Ni. etc. (Fiz,
metal, mctalloved, Vol 7.
181, 185, 1959), and each has a high Curie temperature (Tc) as a single substance (for example, Fe has a high Curie temperature (Tc) of 770").
c), thermal writing is difficult, and the squareness ratio (S) is low (
For example, Fe has a problem of low reproduction output (0.25).

The present invention has been made in view of the above circumstances, and its purpose is to provide a magneto-optical material having a low Curie temperature, a large squareness ratio, and a large transverse Kerr effect.

[Means to solve the problem]

A first magneto-optical recording medium according to the present invention is characterized by having a magnetized film comprising iron, platinum and unavoidable impurities, and having a platinum content of 40 atomic % or less.

Further, a second magneto-optical recording medium according to the present invention is made of iron-platinum, which is solid at room temperature, and contains elements other than iron and platinum, or compounds thereof, and unavoidable impurities, and the content of platinum is 40%.
It is characterized by having a magnetization film with a magnetization of less than a few atomic %.

Further, a third magneto-optical recording medium according to the present invention is characterized in that the underlying material of the magnetized film has a thermal expansion coefficient of 120 x 10-7/'c or less.

[Function] According to the present invention, platinum (Pt) is added to iron (Re), which has a large horizontal Kerr effect but has a high Curie temperature Tc and a low squareness ratio S, as a mouth material for a magnetized film. , the Curie temperature Tc can be lowered while preserving the lateral force effect directly related to the reproduction output.

In this range, the number of atoms of pt is 40 or less, Fe
Although it is inferior to the horizontal Kerr effect of a single substance, it shows the horizontal Kerr effect as a mixture of Fc, l"e, Pt, and Feat, or as an intermediate phase material, whereas when the number of atoms exceeds 40, Fe5P
Due to the mixing of tFeI't, the mesophase material no longer exhibits the transverse Kerr effect.

In addition, the composition ratio of PT is 40 or less in atomic %, especially 10 to
Assuming a u surrounding of 25%, a mixture of Fe, FC3Pt,
It is magnetically homogenized by the mesophase state, and in addition, Fe, P
By adding a third element other than t or a compound thereof, crystal grains are refined, lattice strain is generated, magnetic homogenization is achieved, simultaneous reversal of magnetization is possible, and the squareness ratio is increased ( S・0.7 or higher).

Furthermore, in the present invention, by using a base material having a thermal expansion coefficient smaller than that of the magnetized film, tensile residual stress is induced in the magnetized film, causing crystal grain refinement and magnetostriction. This improves the uniformity of the surface area and further improves the squareness ratio.

Note that the lower limit of the pt content in the magnetized film is not particularly limited, but if the pt content is low, the Curie temperature Tc
It is desirable that the PT content is 10% or more so that the Curie temperature tends to increase and the Curie temperature is 500° C. or less, which is considered desirable in practice.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on drawings showing embodiments.

FIG. 1 is a cross-sectional structural diagram of a magneto-optical recording medium, in which 1 indicates a substrate and 2 indicates a magnetized film. As the substrate 1 serving as the base layer of the magnetized film 2, a material having a coefficient of thermal expansion of 120 x 10-'/''C or less, which is lower than that of the magnetized film 2, such as borosilicate glass or soda glass, is used. Regarding the material The material may be any material as long as it has translucency and satisfies the conditions for the coefficient of thermal expansion described above.

The reason why the coefficient of thermal expansion is set to 120 x 10-'/''c or less is that if it exceeds this value, it will approximate the coefficient of thermal expansion of the magnetized film 2, the tensile residual stress to be applied to the magnetized film will be small, and the squareness ratio will be low. Depends on the decline.

The magnetized film 2 is made of Fe, PT with an atomic percentage of 40 or less, and unavoidable impurities, and is usually laminated to a predetermined thickness (approximately 300 to 3000 layers) on the substrate 1 by sputtering. The structure of the magnetized film 2 is usually an alloy structure of Fe and pt, but it does not necessarily have to be in a solid solution state as an alloy, and may be in a compound or intermediate phase state, for example.

In addition to Fe and 40 or less atomic % of pt, this magnetized film 2 may also contain a third element other than Fe, mainly a metal, or a compound thereof, such as an oxide, a nitride, a carbide, or the like.

The addition means prepares targets for Fe and r' as well as targets for these additives, and simultaneously snorts and tars them. It is desirable that these additives be in a solid state at room temperature due to the manufacturing process of the magnetized film, the environment during use, and other conditions, and the above elements or compounds thereof include simple metals such as Cr, Ni, W, Ta, V, It is preferable to use Zr or a compound thereof. The relationship between the addition amount of an element and the squareness ratio is, for example, for Cr, 1 to 7 atomic % and 0.
A value of 7 or more is obtained.

[Test Example 1] A plurality of materials having different PtMi composition ratios were prepared, and the relationship between the number of pt original atoms and the transverse Kerr effect was investigated.

The sample was heated to an argon (^r) gas pressure of 1 to 30 mTorr.
In a vacuum chamber set at Sputtering was performed at ~5 KW, and 300 to 3000 films were formed on the substrate.

Regarding the transverse Kerr effect, the reflected light intensity change (ΔR/R) when P-polarized light is incident at an incident angle of 45° on the incident plane perpendicular to the magnetization direction of the magnetized film and the direction of saturated magnetization is reversed.
was determined, and this was taken as the value indicating the horizontal car effect. The result is second
As shown in the figure.

FIG. 2 is a graph showing the relationship between the horizontal Kerr effect and the ptMi formation, with the horizontal axis representing the number of pt original atoms and the vertical axis representing the change in reflected light intensity. It is clear from this graph that
, the reflected light intensity changes when the number of pt primitive atoms is 40 or less, l! II
It can be seen that a horizontal Kerr effect is observed.

Note that within the range of static gas pressure in the vacuum chamber of 1 to 30 mTorr, magnetization film thickness of 300 to 3000 people, and input power of 1 to 5 KW, the graph shown in Figure 2 changes slightly to the left and right, but there is no substantial change. Almost the same results were obtained.

[Test Example 2] Using the same sample as that used in Test Example 1, Fe
-The relationship between PtMi composition and Curie temperature (Tc) was investigated.

The results are shown in Figure 3. FIG. 3 is a graph showing the relationship between the Curie temperature and the I'tll composition, with the horizontal axis representing the number of atoms of pt and the vertical axis representing the Curie temperature (Tc). Note that the Curie temperature Tc was measured using a vibrating magnetometer (VSM). As is clear from this graph, the Curie temperature Tc can be set to 500°C or less within the range of 40% to 1O% of the number of pt atoms, which is compared to the Curie temperature of Fe alone, which is 770°C. It can be seen that this can be significantly reduced.

[Test Example 3] The relationship between the composition ratio of pt and the squareness ratio was investigated.

As in Test Example 1, a magnetization layer with a thickness of 500 mm was formed on the substrate by sputtering at a gas pressure of 5 mTorr in the vacuum chamber, and the dependence of the squareness ratio on the PTT formation was measured. The squareness ratio (S) was determined as the ratio of the saturation magnetization (Ms) measured by a vibrating magnetometer (VSM) to the residual magnetization (Mr), that is, S=Mr/Ms.

The results are shown in Figure 4. Figure 4 shows the squareness ratio and p
This is a graph showing the relationship with tm composition, with Pt (atomic %) plotted on the horizontal axis and squareness ratio plotted on the vertical axis. As is clear from this graph, the number of atoms of <pt is 10 to 25%.
It can be seen that a squareness ratio of 0.7 or more, which is required for a magneto-optical recording medium, can be obtained within the range of 0.5%. This is only Fe (p
It can be seen that the squareness ratio is significantly improved compared to the case where the squareness ratio is 0.25.

[Test Example 4] Magnetization II was formed by adding a third element to Fe and Pt, and the relationship between the amount of the third element added and the squareness ratio was investigated.

As in Test Example 1, the gauge gas pressure in the vacuum chamber was
mTorr, Fe target-L to l) and third
A target of Cr, which is an element of Note that the value of the squareness ratio was determined in the same manner as in Test Example 3.

The results are shown in FIG. Figure 5 shows the squareness ratio and l
This is a graph showing the relationship between the addition amount of a third element other than Pt, where the horizontal axis shows the composition ratio (atomic percentage) of the third element, and the seven axis shows the squareness ratio. This is an indication.

It's clear from this graph! It can be seen that the squareness ratio increases as the amount of Cr added increases compared to the case where a+ < is not added.

Note that Ni, W, and Ta are used as the third element instead of Cr.
, VZr, Nh, etc. may be added, and the relationship between their composition ratio and squareness ratio is as shown in Table 1.

table [Test Example 5] The relationship between the thermal expansion coefficient and squareness ratio of the substrate was investigated.

Borous acid glass and hisodium glass were used as substrates with various coefficients of thermal expansion, and the Ar gas pressure in the chamber was 5 mT.
Fe in orr, PC target y l (Pt: 25
A film thickness of 5 % was created on the substrate by spuckling using
A magnetized film of 00 people was formed and used as a sample. The squareness ratio was determined in the same manner as in Test Example 3.

The results are shown in FIG. FIG. 6 is a graph showing the relationship between the squareness ratio and the thermal expansion coefficient of the magnetized film base material, with the horizontal axis representing the thermal expansion coefficient of the substrate and the vertical axis representing the squareness ratio.

As is clear from this graph, the coefficient of thermal expansion is 120×to
It can be seen that a squareness ratio of 0.7 or more, which is required for a magneto-optical recording medium, is obtained at -7,/'C or less.

[Effect] As described above, in the magneto-optical recording medium according to the present invention, since the magnetized film is composed of a component composition containing Fe and pt having an atomic percentage of 40 or less, the transverse Kerr effect is ensured and , can significantly lower the Curie temperature, and Fe, Pt
The squareness ratio can be greatly improved by adding a third element or a compound thereof other than 1,6 and further reducing the thermal expansion coefficient of the substrate to 120 x 10-'/'C or less, and the in-plane magneto-optical This provides an excellent effect by making full use of the characteristics of the recording/reproducing method.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional structural diagram of the magneto-optical recording medium according to the present invention, Fig. 2 is a graph showing the relationship between the transverse Kerr effect and the Pt'2Jl composition, and Fig. 3 is a graph showing the relationship between the Curie temperature and the Pt1M composition. Figure 4 is a graph showing the relationship between the squareness ratio and the PT composition; Figure 5 is a graph showing the relationship between the squareness ratio and the amount of addition of a third element other than Fe and Pt; Figure 6 is a graph showing the relationship between the squareness ratio and the thermal expansion coefficient of the magnetized film base material. 1...Substrate 2...Magnetized film

Claims (1)

[Scope of Claims] 1. A magneto-optical recording medium comprising a magnetized film made of iron, platinum and unavoidable impurities, with the platinum content being 40 atomic % or less. 2. Featuring a magnetized film that is solid at room temperature and is made of iron, platinum, an element other than iron or platinum, or a compound thereof, and unavoidable impurities, and has a platinum content of 40 atomic percent or less. magneto-optical recording medium. 3. The thermal expansion coefficient of the underlying material of the magnetized film is 120×10
3. The magneto-optical recording medium according to claim 1, wherein the temperature is ^-^7/°C or less.