JPH0432209A - Magnetic film - Google Patents

Abstract

PURPOSE:To improve the permeability of a laser beam and obtain a magneto- optical effect by using alloy of rare earth elements and transition metals and oxide of the rare earth elements and/or transition metals as principal constituents and providing prismatic structure and vertical magnetic anisotropy. CONSTITUTION:A prismatic-structure magnetic film consists of, besides the same magnetic materials as conventional, amorphous oxide containing alloy of rare earth elements and transition metals in the form of particulates of diameter as large as 20-500Angstrom to improve the permeability of a laser beam and obtain a higher magneto-optical effect (Faraday effect). The prismatic structure of the magnetic film vertically magnetized provides higher vertical magnetic anisotropy. The prismatic structure of an a-rare-earth-element- transition-metal-alloy thin film containing the alloy of the rare earth elements and transition metals in particulate form forms a film vertically magnetized better than the same film not containing the alloy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic film, and more specifically, it is particularly useful as a magneto-optical recording medium, and furthermore, it is capable of recording and reproducing using a magnetic head instead of a laser beam. The present invention relates to a magnetic film that can be used as a magnetic recording medium for holography and other rewritable holography memory media.

(Prior Art) A magnetic film (magnetic thin film) formed on a suitable substrate (non-magnetic support) is widely used as a recording medium (magnetic recording medium, magneto-optical recording medium).In particular, The recording medium (magneto-optical recording medium) used in the magneto-optical recording method includes:
It is required to have high recording sensitivity, a large magneto-optical effect, the ability to manufacture a large area uniformly and inexpensively, and excellent stability. In addition, the magnitude of the magneto-optic effect is greatest when the direction of magnetization and the direction of light travel are parallel, and the condition of having magnetization perpendicular to the plane satisfies the requirements for perpendicular magnetic recording. This makes it suitable for high-density recording. Therefore, a material with magnetization perpendicular to the plane must be selected for the recording medium.

In response to these demands, many magnetic film materials useful for magneto-optical recording media have been proposed; representative examples include:
Amorphous rare earth element/transition metal alloys such as GdCo, CdFe, TbFe, and TbDyFe are known. However, in a magnetic film made of this amorphous rare earth element/transition metal alloy (hereinafter sometimes abbreviated as "a-rare/transition alloy"), both the rare earth element and the transition metal are easily oxidized, so the performance deteriorates over time. There is a tendency to do so. Therefore, when an a-rare transition alloy film is used, it is necessary to cover this film with a passivation film to prevent oxidation. Further, the a-rare transition alloy film lacks stability and tends to crystallize at a high temperature of about 500° C., resulting in deterioration of properties.

[Problem to be solved by the invention]

The first object of the present invention is to provide a magnetic film that does not cause the above-mentioned disadvantageous phenomena and is particularly useful for magneto-optical recording media. By doing so, the characteristics as a magneto-optical recording medium can be further improved, and a magnetic film that does not easily undergo thermal decomposition is provided.

A third object of the present invention is to provide a magnetic film in which reproduction efficiency, particularly due to the Faraday effect, is enhanced.

[Means for Solving the Problems] The magnetic film of the present invention is mainly composed of a rare earth element/transition metal alloy and an oxide of these rare earth elements and/or transition metals, has a columnar structure, and has a perpendicular magnetic anisotropy. It is characterized by having tropism.

To explain the magnetic film of the present invention in an easy-to-understand manner, it can be said that rare earth elements,
The purpose is to improve the transmittance of laser light and obtain a magneto-optical effect by making a transition metal alloy into fine particles and incorporating it into an amorphous oxide.

To explain this in more detail in comparison with conventional magnetic films, most of the magnetic films for conventional magneto-optical recording media are based on the Kerr effect among magneto-optical effects, and the Kerr effect is due to the effect of magnetic materials. It is determined by the type.

On the other hand, the magnetic film of the present invention is based on the Faraday effect among the magneto-optical effects. Furthermore, the Faraday effect can be reduced by increasing the Faraday rotation angle (θF) by increasing the thickness of the magnetic film.
becomes larger, and the S/N ratio also becomes larger.

Therefore, even though the magnetic film according to the present invention uses some of the same conventional magnetic materials, its structure is different from that of rare earth elements.
A transition metal alloy is mixed into an amorphous oxide in the form of fine particles (2
0 to 500 people) and contained in a columnar structure,
The laser beam transmittance is improved and a better magneto-optical effect (Faraday effect) is obtained.

As mentioned above, the magnetic film of the present invention is (1) a perpendicular magnetization film and (2) exhibits a columnar structure, which contributes more to perpendicular magnetic anisotropy due to the columnar structure. It can be said that As mentioned earlier, the a-rare/transition alloy thin film forms a good perpendicular magnetization film, but it contains rare earth element/transition metal alloy particles and is formed into a columnar structure. This tendency becomes even stronger.

In the present invention, in order to further enhance the perpendicular magnetic anisotropy of the magnetic film exhibiting a columnar structure, the ε-phase MxN (2<x≦3), which is a nitride of a ferromagnetic metal, is used.

or Ni] is preferably present in the film with C-axis orientation. This is thought to be due to the fact that the nitride particles are closely connected magnetically within the columnar structure, further enhancing the perpendicular magnetic anisotropy.

As mentioned above, since rare earth elements and/or transition metal oxides are present in the magnetic film of the present invention from the beginning, the progress of oxidation (rust formation) of rare earth elements and transition metals is further suppressed. Chemically stable. In addition, rare earth elements
The presence of transition metal alloy oxides makes the film hard and scratch-resistant.

In fact, when the magnetic film of the present invention is examined by X-ray diffraction, no diffraction peak is observed, or even if it is observed, only a minute oxide peak is observed. In particular, a film in which the diffraction peak of the ε-phase MxN orientation plane can be observed has extremely good perpendicular magnetic anisotropy. However, the reason for this has not yet been clarified.

The magnetic film of the present invention contains rare earth elements, transition metals, and their alloys in the form of fine particles (estimated to be about 50 particles) that are too small to be observed by X-ray diffraction. The oxides or nitrides of the alloy are contained in such an amorphous combination that they cannot be observed by X-ray diffraction (e.g. Fe-0, Co-0,
(Fe-N, Co-N, etc., and if these are crystals, diffraction peaks will appear).

When C-axis oriented particles of ε-phase MxN are clearly crystallized and contained, a strong diffraction peak of the zero plane is observed, and the smaller the half-width of the rocking curve of this peak, that is, the better the crystal orientation. There is a tendency for the perpendicular anisotropy field to increase.

In the present invention, in order to make it easier to form a magnetic film having a columnar structure, an underlayer may be provided on the substrate (support) in advance. Further, a protective layer 1 reflective layer, a lubricating layer, a dielectric layer, etc. may be provided on the magnetic layer as necessary.

As the support, an appropriate non-magnetic material such as plastic film, ceramic, metal, glass, etc. can be used. The plastics used for the support here include not only heat-resistant plastics such as polyimide, polyamide, and polyethersulfone, but also plastics such as polyethylene terephthalate, polyvinyl chloride, cellulose triacetate, polycarbonate, and polymethyl methacrylate. can.

Further, the shape of the support may be any shape such as a sheet, a card, a disk, a drum, or a long tape.

The dielectric layer (effective for enhancement effect) is 5in2,
Tie, Ti0N, Ag5iO1TiN, AflSiN
, BN, SiN, AQN.

Examples include AffSiON, Sin, 5iON, etc.

The lubricating layer includes a carbon layer, molybdenum dioxide, tungsten disulfide, an α-olefin polymer, and an unsaturated hydrocarbon that is liquid at room temperature (a compound in which an n-olefin double bond is bonded to the terminal carbon; carbon number is 20).

Examples include fatty acid esters consisting of a monobasic fatty acid having 12 to 20 carbon atoms and a monohydric alcohol having 3 to 12 carbon atoms.

Materials for the reflective layer include Au, Afi, Ag, Pt, and Cr.
, Nd, Ge, Rh, Cu, TiN, etc. are used.

The above-mentioned layers including the magnetic film are manufactured by a thin film forming method such as a vacuum evaporation method, an ion plating method, a sputtering method, or a CVD method. The thickness of each layer is 14 or less, preferably 0.05 to 0.5I! S<Leprosy is appropriate.

Actually, in order to make the magnetic film according to the present invention, for example, RF
A transparent magnetic film may be deposited on a substrate using a sputtering device using the above-mentioned ferromagnetic metal and transparent substance (oxide of a rare earth element and/or transition metal) as a target material.

〔Example〕

Example 1 A transparent magnetic film with a thickness of approximately 2000 mm was formed on a disk-shaped polycarbonate substrate using an ion beam sputtering apparatus at a rotation speed of 2 rpm and under the following conditions.

Target GdFe (Gd 10at+
s%) Substrate heating None Ionized gas Ar (100%) introduced gas
Air base pressure 8 X 10-7 Torr Ion gun current 1.2 A Ion gun voltage 9.5 KV Ion incident angle 30 degrees Introduced air pressure 2 X 10-' Torr
Target-Substrate Distance 14 When this magnetic film was examined by X-ray diffraction, no diffraction peak was observed. When the cross section was examined using the TEN method, a columnar structure with a diameter of about 150 to 300 people was observed.

The light transmittance was 45% (λ=800 nm). VSM
The magnetic properties investigated were He4 (coercive force) = 12000e
, , Hc# (coercive force) = 3000s, Ms (saturation magnetization) = 520e+++u/ec, 5q1 (squareness ratio) =
0.22, Hx (perpendicular magnetic anisotropy field) = 4. I K.O.
e, and it was confirmed that it was a perpendicularly magnetized film. The compensation temperature was 190°C.

Next, the Faraday rotation angle was measured using a semiconductor laser (λ = 780 nm) while applying a maximum magnetic field of 12 KOe to this magnetic film, and it was found to be 1.3 deg/-. Even when measured after being immersed in the solution, there was no change in the above characteristics.

Example 2 Ar (75%) + N, (25%) as ionized gas
A transparent magnetic film was formed in the same manner as in Example 1 except that the ion gun voltage was 9 KV and the ion gun current was 2 mA.

This magnetic film has (002) of FaxN (2<X≦3).
A (004) diffraction peak was observed. Moreover, the diameter of the columnar structure was 150 to 300 people and was almost the same as in Example 1, but the columnar structure was observed more clearly. The light transmittance was also the same as in Example 1.

The magnetic properties investigated by VSM are Hc, = 13500s, H
c#=2900s, Ms=500emu/cc, S
g, = 0.26, Hg = 5.3 KOe, and it was confirmed that it was a perpendicularly magnetized film. The compensation temperature was 210°C. The Faraday rotation angle was 3.9 deg/IJs. This magnetic film was immersed in a 5% NaCQ solution for one month and then measured, and there was no change in the above characteristics.

Comparative Example 1 A transparent magnetic film was formed in the same manner as in Example 1, except that Fe (99.99%) was used as the target and the introduced air pressure was 8 x 10-' Torr.

As for the diffraction peaks of this magnetic film, a peak of FeO (200) and a broad peak of α-Fe (110) were observed.

However, a columnar structure similar to that in Example 1 was observed although it was unclear. The transmittance was 44% (λ=800 nm). However, the magnetic properties investigated by VSM are Hc, = 2900e,
Hc#=1300s, Ms=660 emu/cc,
sq, :o, 1:l, Sq#"0.13, Hk=2°8 KOe, and it was recognized that it is an isotropic magnetized film. The magnetization does not become 0 until SOO℃, but slightly changes. The magnetization gradually decreased, and at 500° C., it was 75% of the saturation magnetization at room temperature.

The Faraday rotation angle was 0.1 deg/Ila. However, there was no change in this magnetic film even when it was measured after being immersed in the NaCM solution for one month.

〔Effect of the invention〕

The magnetic film of the present invention is a transparent magnetic film that has large perpendicular magnetic anisotropy and magneto-optical effect (Faraday effect), and also has an appropriate compensation temperature, so that highly sensitive recording and erasing can be performed. It is chemically stable and useful as a magnetic film for magneto-optical recording.

Patent applicant Rico Co., Ltd.

Claims (2)

[Claims] (1) Magnetism characterized by having a rare earth element/transition metal alloy and oxides of these rare earth elements and/or transition metals as main components, exhibiting a columnar structure, and having perpendicular magnetic anisotropy. film. (2) The magnetic film according to claim 1, wherein the columnar structure contains a C-axis oriented transition metal nitride.