JPH02107748A - Thin amorphous alloy film - Google Patents

Abstract

PURPOSE:To provide high coercive force and superior magneto-optical characteristics by adding specific amounts of Pd or Pd and Pt to the composition of a thin film of RE-Fe-Co amorphous alloy. CONSTITUTION:A thin amorphous alloy film having an easy magnetization axis perpendicular to a film surface has a composition represented by a formula, where RE consists of >=at least 50atomic% Tb and Dy and the balance Nd, Gd, Ce, Eu, Pr, Ho, and Sm and the symbols (a), (x), (y), and (z) stand for >0-1, >0.2-<0.7, 0.15-0.3, and >0.3-1.0, respectively. By this method, the thin amorphous alloy film having superior magneto-optical characteristics, such as large Kerr rotation angle and large Faraday rotation angle, and superior oxidation resistance and further improved in reflectivity and sufficiently reduced in Curie temp. can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an amorphous alloy thin film having excellent oxidation resistance. The present invention relates to an amorphous alloy thin film having a tendency to oxidize.

Technical background of the invention and its problems Transition metals such as iron and cobalt and terbium (T b)
, an amorphous thin film made of an alloy with a rare earth element such as cadrinium (Gd) has an axis of easy magnetization in the direction perpendicular to the film surface, and the film surface is entirely magnetized in one direction. is known to be able to form small reversed magnetic domains with opposite directions.

By associating the presence or absence of this inverted magnetic domain with "1" and "0", it becomes possible to record digital signals on the amorphous thin film as described above.

For example, Japanese Patent Publication No. 57-20691 discloses an amorphous thin film made of a transition metal and a rare earth element used as such a magneto-optical recording medium.
A Tb-Fe based alloy amorphous thin film containing the following is disclosed.

Also, an alloy amorphous thin film made by adding a third metal to Tb-Fe is also used as a magneto-optical recording medium. Further T
Magneto-optical recording media such as b-Co and Tb-Fe-Co are also known.

Magneto-optical recording media made of these alloy amorphous thin films have excellent recording and reproducing properties, but during use, these amorphous thin films undergo oxidation and their properties change over time. There were major practical problems.

The mechanism of oxidative deterioration of magneto-optical recording media made of alloyed amorphous thin films containing transition metals and rare earth elements is as follows.
For example, Journal of the Japanese Society of Applied Magnetics, Vol. 9, No. 2, No. 93.
It has been discussed on pages 96 to 96, and it has been reported that there are three types as shown below.

b) Pitting corrosion Pitting corrosion refers to the formation of pinholes in an amorphous thin film of an alloy. This corrosion mainly progresses in a high humidity atmosphere, and for example, it progresses significantly in Tb-Fe systems, TbCo systems, etc. do.

) A surface oxidation layer is formed on the amorphous thin film of the surface oxidation alloy, and the Kerr rotation angle θ
k changes over time, and the Kerr rotation angle θk eventually decreases.

C) Selective oxidation of rare earth metals The rare earth metals in the alloy amorphous thin film are selectively oxidized, and the coercive force He changes greatly over time. In order to prevent this, various methods have been tried in the past.

For example, alloy amorphous thin films can be made of Si3N4, SiO,
A method of creating a three-layer structure sandwiched between anti-oxidation protective films such as St 2 O and AgN is being considered. However, this oxidation-preventing protective film is expensive and time-consuming to form, and even if this protective film is formed, it is not always possible to sufficiently prevent oxidative deterioration of the amorphous alloy thin film. there were.

In addition, in order to improve the oxidation resistance of the thin film, a third layer is added to the amorphous thin film of alloys such as Tb-Fe and Tb-Co.
Various methods of adding metals have been attempted.

For example, in the journal of the Japanese Society of Applied Magnetics mentioned above, Tb-Fe
Or Tb-Co, Co, Ni, PC.

By adding a third metal such as Ag, Cr, Ti in an amount up to 3.5 at%, Tb-Fe system or T
Attempts have been made to improve the oxidation resistance of b-Co alloy amorphous thin films. and TI>-Fe or Tb-
Adding small amounts of Co, Ni, and PL to Co is effective in preventing surface oxidation and pitting corrosion, but it is effective in preventing selective oxidation of Tb, a rare earth metal, in the amorphous thin film of this alloy. is reported to be ineffective. This means that T
b-Fe or Tb-Co with a small amount of Co, NiP
When t is added, in the resulting alloy amorphous thin film,
This means that Tb is selectively oxidized and the coercive force He changes greatly over time. Therefore T
Even when a small amount of up to 3.5 atomic % of Co5NiPt is added to b-Fe or Tb-Co, the oxidation resistance of the resulting alloy amorphous thin film is not sufficiently improved.

Also, the 9th Academic Lecture Summary of the Japanese Society of Applied Magnetics (1985)
(November 2012), page 209, there is a study of Tb-Fe or T
An alloy amorphous thin film is taught in which PL, Ag, Cr, and Ti are added to b-F B-CO in amounts up to 10 atomic percent. However, Tb-Fe or Tb-Fe-
Co with amounts of Pt, A, pSCr, Ti up to 10 atomic %
Although surface oxidation and pitting corrosion can be prevented quite effectively by adding He, the oxidation prevention property against selective oxidation of Tb in the resulting amorphous alloy thin film is not sufficient, and the coercive force He also decreases over time. There still remained the problem that the coercive force He changed greatly and eventually the coercive force He decreased significantly.

Furthermore, in JP-A-58-7806, Pt
A magnetic thin film material comprising a polycrystalline thin film having a composition of Co and containing 10 to 30 at. % of pt is disclosed.

However, since this polycrystalline thin film with a composition of PtCo is polycrystalline, it requires heat treatment such as annealing after film formation, and the grain boundaries between crystals may generate noise signals. This polycrystalline thin film had a problem in that it had a high Curie point.

Furthermore, in Japanese Patent Application Laid-Open No. 58-73746, Tb (
FeCo) (0.15≦X in the formula
magneto-optical recording medium consisting of an amorphous alloy thin film having an axis of easy magnetization perpendicular to the film surface, expressed as is disclosed. However, in the magneto-optical recording medium disclosed in this publication, 0.50<
When it comes to y, the Curie point is too high and it is said to be impractical, but if 0.5<y and a magneto-optical recording medium with excellent oxidation resistance can be obtained, then The practical value is extremely large.

Purpose of the Invention The present invention aims to solve the problems associated with the prior art as described above. It is an amorphous material that has excellent oxidation resistance, does not change its coercive force or Kerr rotation angle over time, has high reflectance, and has a sufficiently low Curie temperature. The purpose is to provide alloy thin films.

Summary of the Invention The amorphous alloy thin film having an easy axis of magnetization perpendicular to the film surface according to the present invention has the following structure: [pd, Pt, -a] y [RE (re Co)] -
[11[1-z z l-x 1-y (wherein, R
At least 50 atomic % of E is Tb and/or D
y, and the remainder are Nd and Gd.

Co, Eu, Prs Ho or S11, 0kua
≦1.0.2<x<0.7.0.15≦y≦O13,0
, 3<z≦1.0).

The amorphous alloy thin film as described above according to the present invention has excellent magneto-optical properties such as a large coercive force and a large Kerr rotation angle and a large Faraday rotation angle, and has excellent oxidation resistance.
It has an excellent property that the coercive force or Kerr rotation angle does not change over time.

Furthermore, compared to an amorphous alloy 1-y y L-x thin film having a composition of Tbx (FeCo), the Curie temperature is sufficiently lower and it has practically excellent properties.

Detailed Description of the Invention The amorphous alloy thin film having an easy axis of magnetization perpendicular to the film surface according to the present invention is [PdaPtl,].

[R[E(FeCo)]X
l-z z L2! ■-y
(In the formula, RE is at least 50 atomic % or more of Tb and/or Dy, and the remainder is Nd, Gd, Ce, Eu
, Pr, Ho or Sm, 0kua≦1, Q,
2<x<0.7. and
At least 80 atomic % or more preferably 90 atomic % of RE
The above is Tb, and the rest are Dy, Nd, Gd, and Ce.

It is an amorphous alloy thin film that is EusPrSHo or SII.

Next, such an amorphous alloy thin film will be explained.

(i) Fe and Co are 1-X (however, 0.2<
x<0.7, preferably 0.25<x0.6).

FB is 0 to 30 atomic% with respect to the total amount of Fe and Go.
Co is present in an amount of less than 20 to 5 atom %, preferably more than 30 atom %, up to 100 atom %, preferably 50
It is present in an amount of ~80 atom %.

In the amorphous alloy thin film according to the present invention, T b-F e-C
By adding a specific amount of Pd or both Pd and pt to the o-based amorphous alloy thin film, the Curie point can be lowered, and the composition dependence of the Curie point or magnetic compensation temperature can be reduced.

Note that Nl may be contained in an amount of 5 atomic % or less, preferably 3 atomic % or less, based on the total amount of Fe and Co.

(i) The amorphous alloy thin film according to the present invention contains Pd or both Pd and pt.

Pd or both Pd and pt are present in the amorphous alloy thin film in an amount of 15 atomic % or more and 30 atomic % or less, preferably 18 atomic % or more and 25 atomic % or less.

In addition, Pd and pt refer to their content ratios as Pd and pt.
When expressed as Pi, 1, Ova≦1. Pd
When the content ratio of a is 0.2<a<1, an economically efficient amorphous alloy thin film can be obtained.

When the content of Pd or both Pd and pt is in the range of 15 atomic % or more and 30 atomic % or less, the resulting amorphous alloy thin film has excellent oxidation resistance, or the coercive force Hc decreases over time. It has the advantage that it does not change significantly and a sufficiently high C/N ratio can be obtained with a small bias magnetic field.

(ii) The amorphous alloy thin film according to the present invention includes the above (i)
and (i) plus at least one rare earth element (
RE).

This RE contains at least 50 at% or more of Tb and/or
Or Dy, with the remainder being Nd and Gd.

At least one element selected from the group consisting of Ce, Eu, Pr, Ho, or Sm. Preferably RE 8
0 atomic % or more is Tb, the balance is Dy, Nd, Gd,
Ce5EuSPr, Ho or 5I11. More preferably, 90 atomic % or more of RE is Tb, and the remainder is Dy, NdSGd.

Ce, Eu, Pr, Ho or Sm.

The above rare earth element RE is such that when the amorphous alloy thin film is expressed by the above formula [T], Q, 2<X, 0.7, preferably 0.25<x<0.6. Exists in quantity.

An alloy thin film having the composition described above has an axis of easy magnetization perpendicular to the film surface, and in most cases is an amorphous thin film that exhibits a rectangular loop with good Kerr hysteresis and is capable of perpendicular magnetic and magneto-optical recording. This can be confirmed by wide-angle X-ray diffraction. Here, if X≦O62 and X≧0.7, Kerr hysteresis tends not to show a good square loop, which is not preferable.

In this specification, a square loop with good Kerr hysteresis means the saturated Kerr rotation angle (in θ), which is the Kerr rotation angle at the maximum external magnetic field, and the residual Kerr rotation, which is the Kerr rotation angle at zero external magnetic field. The ratio θ to the angle (2 to θ)
This means that 1 in 2/θ is 0.8 or more.

Furthermore, the amorphous alloy thin film according to the present invention as described above has excellent oxidation resistance, and as shown in FIG.
Even if an amorphous alloy thin film having a composition of L to T b a3F e 22CO25 is kept in an environment of 85° C. and relative humidity of 859 for 240 hours or more, its coercive force hardly changes. On the other hand, when an amorphous alloy thin film having a composition of Tb Co or T b 25 F eee CO9 that does not contain Pd or both Pd and pt is kept in an environment of 85° C. and 85% relative humidity, The coercive force changes greatly over time. Furthermore, even if this environmental test is continued for 1000 hours, P
In systems containing d or both Pd and pt, the coercive force hardly changes. From these things, P
It can be seen that the system containing d or both Pd and pt suppresses the selective oxidation of rare earth elements.

Furthermore, the change in θ after the environmental test was small, indicating that surface oxidation was prevented, and observation of the film surface using a microscope revealed that pitting corrosion was also suppressed.

Also, P d 12P L e Tb 34F e 2
1CO27, P d t5P j ttT b 35F
An amorphous alloy thin film having a composition such as 'a tgc O23 also has excellent oxidation resistance, and its coercive force hardly changes.

As described above, the amorphous alloy thin film according to the present invention has extremely excellent oxidation resistance. Therefore, when using this amorphous alloy thin film, it is not necessary to provide an oxidation-preventing protective film on the amorphous alloy thin film. It has an excellent property that it is not necessary.

In the present invention, various other elements may be added to improve the Curie temperature, compensation temperature, He and θ, or to reduce costs.

These elements can be substituted for the heavy rare earth elements at a ratio of, for example, 50 atomic %.

Examples of other elements that can be used in combination are: (1) 3d transition elements other than Fe and Co Specifically, Sc, TI VSCr, Mn.

Ni-CusZn is used.

Among these, Ti, Ni, CuSZn, etc. are preferably used.

(II) 4d transition elements, specifically, Y% Z r −, N b s Mo
sTe %Ru, RhSAg, Cd are used.

Among these, Zr and Nb are preferably used.

(m) 5d transition elements other than PL Specifically, Hf', Ta, W, Re, Os.

Ir, Au, and Hg are used.

Among these, Ta is preferably used.

(V) WB group element Specifically, B, AΩ, Ga, In, and Tl are used.

Among these, B and A9 SGa are preferably used.

(VI) Group IVB elements, specifically C, S! Ge, 5nSPb is used.

Among these, St, Ge, Sn, and Pb are preferably used.

(■) VB group element Specifically, NSP, As5Sb, and Bl are used.

Among these, sb is preferably used.

(■) WB group elements Specifically, S, 5eSTe, and Po are used.

Among these, Te is preferably used.

Next, a method for manufacturing an amorphous alloy thin film according to the present invention will be explained.

The substrate temperature is maintained at about room temperature, and a composite target in which chips made of each element constituting the amorphous alloy thin film according to the present invention are arranged at a predetermined ratio or an alloy target having a predetermined composition is used by sputtering method or electron beam. This substrate (
(The substrate may be fixed or rotating)
By depositing an amorphous alloy thin film of a predetermined composition thereon, the amorphous alloy thin film according to the present invention can be formed.

As described above, the amorphous alloy thin film according to the present invention can be formed at room temperature, and there is no need to perform heat treatment such as annealing after film formation in order to have an axis of easy magnetization perpendicular to the film surface. .

Note that, if necessary, the amorphous alloy thin film can be formed on the substrate while heating the substrate temperature to 50 to 600°C or cooling it to -50°C.

Further, during sputtering, the substrate can be biased to a negative potential. In this way, ions of an inert gas such as argon accelerated by an electric field will strike not only the target material but also the perpendicularly magnetized film being formed, resulting in a perpendicularly magnetized film with excellent properties. There is.

Since the amorphous alloy thin film of the present invention has an axis of easy magnetization perpendicular to the film surface, it can be used in the field of magnetic recording materials, such as perpendicular magnetic recording films, magnetic bubble memories, or magneto-optical recording films, using the magneto-optic effect. It can be applied to various fields such as optical modulators.

For example, in the field of perpendicular magnetic recording, it is expected to be used in the recording films of vertical flexible disks and rigid magnetic disks, and in magneto-optical recording, the Kerr rotation angle or Faraday rotation angle is used to generate information signals or still images. magneto-optical disks, magneto-optical cards,
It is expected to be used in magneto-optical tapes. It is also expected to be used in optical modulators that control the Kerr rotation angle and Faraday rotation angle by controlling an external magnetic field, and activate photovoltaic cells by changing the amount of reflected light and transmitted light.

A case where the amorphous alloy thin film of the present invention is applied as a recording film of a magneto-optical disk will be described below.

The amorphous alloy thin film of the present invention is a perpendicularly magnetized film having an axis of easy magnetization perpendicular to the film surface, and in many cases has a square Kerr hysteresis loop, so that it can be easily magnetized under the absence of an external magnetic field. Since θk is almost the same as the saturation θ at the maximum external magnetic field and the coercive force He is large, it is suitable as a magneto-optical recording film.

Furthermore, a good value of θk means that a good value of θr, and therefore it can be used in either the Kerr effect type or the Faraday effect type.

Moreover, since the amorphous alloy thin film of the present invention has excellent oxidation resistance, it has better oxidation resistance than the conventional T b-F! 3% T b Fe-C
It is not necessarily necessary to use a protective film for preventing oxidation as in the case of heavy rare earth-3d transition metal alloy thin films such as O.

Furthermore, it is not necessary to use anti-oxidation materials for the substrate in contact with the recording film, other functional films (for example, enhancement film, reflective film), or adhesive layers for bonding.

Furthermore, when forming enhancement films, reflective films, etc., in addition to dry film formation methods such as vacuum evaporation and sputtering,
This means that wet film formation such as a spin code method or a spray method, which could not be performed conventionally, may be performed.

Therefore, the structure of a magneto-optical disk using the amorphous alloy thin film of the present invention as a recording film is as follows: (i) substrate/recording film (i) substrate/enhancement film/recording film (ii) U plate/recording film/reflection film Film (1■) Substrate/enhanced film/recording film/reflective film (v) Substrate/enhanced film/recording film/enhanced film/reflective film or protection for imparting only scratch resistance to the outermost layer on the recording film side It becomes possible to create a structure with a coat or protective label formed thereon.

Here, the enhancement film may be made of any organic or inorganic material as long as its refractive index is greater than the refractive index of the substrate.

A specific example of the enhancement film is T I O2,5IO
1TI O, Zn 01 ITO1Z r O2, Ta
Oxides such as OSNb O, CeOXSnO2, TeO, SI N , A, l! Nitride such as N, BN, Z
Sulfides such as nS, CdS, Zn5eSSt C55
There are l, etc. Further, transparent materials having a Faraday effect such as ferrites such as cobalt ferrite and garnets such as B1-substituted garnent may be used as the enhancement film. In addition to inorganic materials such as glass and aluminum, substrates can also be made of polymethyl methacrylate, polycarbonate, polymer alloys of polycarbonate and polystyrene, amorphous polyolefins as shown in USP 4,614,778, poly4-methyl-1-pentene, epoxy resins, and Organic materials such as ether sulfones, polysulfones, polyetherimides, etc. can also be used.

Furthermore, the configuration of the magneto-optical disk is as follows (i) to (V
) The structure is not limited to the above structure, but a base layer or a high permeability soft magnetic film may be laminated as necessary, and it is also possible to use a laminated structure in addition to a single plate.

Effect of the invention The amorphous alloy thin film according to the present invention is [PdaPt,,].

[RE (FoCo)]
...[11x 1-z z L-x 1-
y (wherein, RE is at least 50 atomic % Tb and/or Dy, and the remainder is Nd, Gd, Ce5E
uSPr, Ho or Sm, 0kua≦1.0.2
It has excellent magneto-optical properties such as a large angle of ＜x＜0.7. It has an excellent property of not causing any damage. On top of that,
Compared to an amorphous alloy 1-y y l-x thin film having a composition of Tbx (FeCo), the Curie temperature is sufficiently lower and it has practically excellent properties. Furthermore, when forming the amorphous alloy thin film according to the present invention on a substrate, it is possible to form the film at room temperature, and there is no need for heat treatment after film formation.

The present invention will be explained below with reference to examples, but the invention is not limited to these examples.

Experimental Examples 1 to 8 The present experimental examples relate to Pt-Tb-Fe-Co-based amorphous alloy films.

As a target, a composite target in which Pt1Fe and Tb chips are arranged at a predetermined ratio on a Co target is used.
An amorphous alloy thin film was formed to a thickness of 1,000 mm by DC magnetron sputtering while controlling the temperature to be around room temperature (°C).

The film forming conditions were A: 5mTorr pressure, Ar flow! 35e
effi, the vacuum attainment was 5×10 = Torr or less.

The crystalline state of the obtained alloy thin film was measured by wide-angle X-ray diffraction, and the composition was determined by ICP emission spectrometry.

In addition, the Kerr rotation angle is the residual Kerr rotation angle at zero external magnetic field, which is determined by n1 from the glass substrate side, using the oblique incidence method (λ = 633 nm).
) was measured. The specific flll+llll ascending device for the oblique incidence method is described in "Measurement Techniques for Magnetic Materials" supervised by Aibe Yamakawa (published by Trikebbs Co., Ltd. on December 25, 1985), No. 26.
It is described on pages 1 to 263.

Furthermore, the Curie temperature (
Tc ) and coercive force were measured and shown in Table 1 along with each value.

Furthermore, in order to confirm the oxidation resistance of the amorphous alloy thin film of the present invention, the film was deposited on a glass substrate at 85°C.
An environmental test was conducted in which the car was left in an oven under high temperature and high humidity conditions at 85% RH for 240 hours, and the Kerr rotation angle (
When we measured θk), reflectance (R), and coercive force (He) and compared them with the initial values θko, Ro, and Hco before the test, we found that θkSR, He was almost the same as θko, RoxHco, respectively. It was the same.

Comparative Examples 1 to 3 In Examples 1 to 7, Pd or pt was not used and Table 1
Examples 1 to 7 were carried out in the same manner as in Examples 1 to 7, except that an amorphous alloy thin film having the composition shown in was formed on a glass substrate.

The physical properties of the obtained amorphous alloy thin film were measured in the same manner as in Examples 1 to 7.

The results are shown in Table 1.

From Table 1, even if the Z values are almost the same, the Curie temperature (T
It can be seen that c) can be lowered.

[Brief explanation of the drawing]

FIG. 1 shows (Pd1oPt1oTb33F) according to the present invention.
O2□Co2. ) changes in coercive force and T related to comparative examples
b 25 CO75 and T b 25 F e e
FIG. 3 is a diagram showing changes in coercive force of e CO-9.

Claims (1)

[Claims] 1) [Pd_aPt_1_-_a]_y [RE_x(Fe_1_-_zCo_z)_1_-_x
]_1_-_y (wherein, RE is at least 50 atomic % Tb and/or Dy, and the remainder is Nd, Gd
, Ce, Eu, Pr, Ho, or Sm, and 0<a
≦1, 0.2<x<0.7, 0.15≦y≦0.3, 0
．． 3<z≦1.0), an amorphous alloy thin film having an axis of easy magnetization perpendicular to the film surface. 2) The amorphous alloy thin film according to claim 1, wherein at least 80 atomic % or more of RE is Tb.