JPH04186807A - Magnetic film - Google Patents

Abstract

PURPOSE:To form the title magnetic film having the enhanced characteristics as a magneto-optical recording medium further avoiding the thermal cracking and oxidation due to the heating step using laser beams by a method wherein a transparent and non-magnetic oxidation preventive film is provided on the surface of a specific magnetic body thin film having the vertical magnetic anisotropy formed directly on a non-magnetic supporting body or through the intermediary of a reflected layer. CONSTITUTION:The title magnetic film is columnarly structured of a component mainly comprising metallic (M) fine particles selected from Fe, Co and Ni formed directly on a non-magnetic supporting body or through the intermediary of a reflected layer, a non-magnetic body having an M-O coupling and a C axially oriented crystalline nitride represented by MxN2<X<=3 while a transparent non-magnetic oxidation preventive film is provided on the surface of a magnetic body thin film having the vertical magnetic anisotropy. For example, an Al film about 1500Angstrom thick is formed on a polycarbonate disc-made basic body using a vacuum evaporation device and then the magnetic body thin film also about 1500Angstrom thick is formed using an ion beam sputtering device as well as Fe, N2+Ar and air respectively for a target material, an ionization gas and a leading-in gas. Finally, an SiAlON film about 1500Angstrom thick is provided on the magnetic body thin film.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magnetic film, and more particularly, it is particularly useful as a magneto-optical recording medium, and more particularly, it is a magnetic recording medium that performs recording and reproduction without using laser light. The present invention relates to a magnetic film that can be used as a medium or as a rewritable memory material for holography.

[Conventional technology]

A magnetic film (magnetic thin film) formed on a suitable substrate (non-magnetic support) is 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 has high recording sensitivity, a large magneto-optic effect (Faraday effect, Kerr effect), and a large area that is homogeneous. In addition, the magneto-optic effect is greatest when the direction of magnetization and the direction of light propagation are parallel. Also,
The condition of magnetization perpendicular to the plane also satisfies the requirements for perpendicular magnetic recording, making it suitable for high-density recording. Therefore, a material must be selected that has magnetization perpendicular to the plane of the medium.

Due to these demands, the magnetic material used in perpendicular magnetic recording media (Fugenetoplumbite type Ba ferrite with a typical hexagonal close-packed (HCP) structure) is used as the material for the magnetic film in magneto-optical recording media.・) or use (
2) MnBi, MnCuB1. MnGaGe, MnA
QGe, PtCo (polycrystalline): (YBi)3(Fe
Ga) so+□ (single crystal); GdCo, GdFe,
TbFe, GdTbFe, TbDyFe (amorphous), etc. are used.

However, depending on the material used, the magnetic films in (]) and (2) above may be difficult to form at low substrate temperatures, or may have a large magneto-optic effect in the wavelength range of semiconductor lasers (for example, 780n [11,830nm, etc.)]. It has some drawbacks, such as not being able to obtain high signal-to-noise ratios, not being able to obtain high signal-to-noise ratios, or having concerns about stability.

As a result of advances in the development of magnetic materials free from such inconvenient phenomena, iron nitride has recently attracted attention. This iron nitride does not rust, is ferromagnetic, and has magnetic anisotropy perpendicular to the substrate, so it is used as high-density magnetic recording media such as recording tapes, audiotapes, and mass storage devices for computers. It has been proposed to apply (JP-A No. 55-33093, No. 59-228705, No. 60-7602), No. 61-110328, No. 62
Publications such as No.-103821).

However, the nitride magnetic materials that have been proposed so far have mainly been used for perpendicular magnetic recording media focusing on their perpendicular magnetic anisotropy, and their application to magneto-optical recording media has largely been abandoned. is the reality.

[Problem to be solved by the invention]

An object of the present invention is to improve the characteristics of a magneto-optical recording medium by controlling the film structure, and to provide a magnetic film that does not undergo thermal decomposition or oxidation due to heating using laser light. be. Another object of the present invention is to provide a magnetic film with improved reproduction efficiency, particularly due to the Faraday effect.

[Failure to solve the problem]

The magnetic film of the present invention includes a nonmagnetic material having a 1M-0 bond with fine particles of a metal (M) selected from Fe, Co, and Ni formed directly or via a reflective layer on a nonmagnetic support;
A transparent non-magnetic anti-oxidation film is provided on the surface of a magnetic thin film having a columnar structure mainly composed of nitride of C-axis oriented crystals expressed by xN (2<X≦3) and having perpendicular magnetic anisotropy. It is characterized by being set up.

Incidentally, the present inventor previously proposed a magnetic thin film without the above-mentioned oxidation prevention film (Japanese Patent Application No. 1-135575).
issue). The magnetic film is made of Fe formed on a non-magnetic support,
At least one metal (M) selected from Co and Ni
It has a columnar structure mainly composed of seed nitride (MxN (2<x≦3)), and within the columnar structure, the C-axis oriented metal nitride is surrounded by an amorphous nonmagnetic material. It is said that it has.

The structure of the magnetic thin film proposed above is substantially or partially the same except for the anti-oxidation film of the present invention, although there are some differences in expression.

However, in the magneto-optical recording medium in which the magnetic thin film proposed above is provided on a non-magnetic support directly or via a reflective layer, the C/N ratio gradually decreases after multiple recording and reproducing operations. We have now confirmed that the cause of this is oxidation of the magnetic film due to heating with laser light or the like. The present invention has been made based on this recognition.

The present invention will be explained in more detail below. Generally, the magnetic thin film according to the present invention is formed on a non-magnetic support directly or via a reflective layer, and is mainly used for magneto-optical recording media. However, instead of the reflective layer, an amorphous rare earth/transition element alloy thin film may be formed between the magnetic thin film and the nonmagnetic support.

By the way, the Japanese Patent Application Laid-Open No. 1983-1983, which was mentioned earlier in the section on the prior art,
Publication No. 228705 describes a magnetic recording medium mainly made of hexagonal iron nitride having perpendicular magnetic anisotropy, which contains Ni, Co, etc. in a range of ]Oalomic% or less. , the nitrogen content in the magnetic film is 20~
It has been clarified that 32alomic% is preferable. The nitrogen content in the latter magnetic film is 20-
The reason why it is limited to 20-32 alo% is simply because the entire film is made of iron nitride (Fe3N and/or Fe2N). Furthermore, this document does not specify the thermal characteristics or the Curie temperature (temperature at which magnetization disappears), but the film structure is columnar with crystal grains grown perpendicular to the film surface, like the co-Ct film. It merely states that the structure is desirable.

Hexagonal iron nitride (the same applies to hexagonal cobalt nitride and macrogonal disokel nitride) has a Curie temperature of 200 to 300°C when its film is heated, but when heated above the Curie temperature, Nitrogen is extracted from α-Fe
As a result, the perpendicular magnetization film shifts to the horizontal magnetization film, and the saturation magnetization also increases by two to three times. For example, iron nitride exhibits a Curie temperature (Tc) of about 295° C., but when this iron nitride is heated above the Curie temperature (Tc), its saturation magnetization increases significantly. When this iron nitride film with increased saturation magnetization is subjected to X-ray diffraction, it is found that it has 6 planes of MxN (002).
The diffraction peak of α-Fe disappears, and the diffraction peak of α-Fe appears. Although an iron nitride film in this state can be used as a perpendicular magnetic recording medium that uses a magnetic head for recording, reading, and erasing without heating, it cannot be used as a magneto-optical recording medium that is heated and recorded with laser light. cannot be said to be useful.

Nevertheless, the fact that such inconveniences are not observed in the magnetic thin film according to the present invention suggests that due to the adoption of a specific film structure, nitrogen cannot escape from the film or is difficult to escape from the film by heating. .

This phenomenon was discovered by adding various elements to hexagonal nitrides of ferromagnetic metals (Fe, Co, Ni) to reduce the saturation magnetization and further increase the perpendicular magnetic anisotropy field (14k). It was discovered that the film structure has a columnar structure formed directly above the surface of the non-magnetic support, and the film structure is made of nitride [Mx
N (2<x≦3)] is C-axis oriented, and it has become clear that this can be achieved by employing a nonmagnetic material having an M-0 bond in place of the above element.

The nitride represented by the above formula (Mx (2<x≦3)) is C
Axially oriented crystallites (CBs + allite tail crystal particles)
The size of this thing is about 5 OA, and the diameter of the pillars of the columnar structure is about 150 to 300 Å. Each nitride particle is a crystal of E-Japanese compound, and is oriented along the C axis. Inside the columnar structure, the oriented crystals of nitride are closely connected magnetically. Note that the surface gap is iron nitride2,19
People, cobalt nitride2. ]7A, nickel nitride 2, ]4A
It is.

In fact, when a cross section of the membrane is viewed with a TEM (transmission electron microscope) at a magnification of several million times, a columnar shape is clearly recognized. Furthermore, F
Ferromagnetic metal elements such as e, Co, and Ni are contained in the columnar structure with their own fine particles and nonmagnetic bonds such as M-0.

By adopting such a structure, the demagnetizing field is easily canceled, the transparency of the laser beam is improved, and the interface between the individual pillars that have grown allows heat to spread more vertically than horizontally. As a result, the extent of the recording area in the plane direction is reduced, and even higher density recording can be performed.

Further, according to the magnetic thin film according to the present invention, the MxN(
Since the nitride represented by 2<x≦3) is surrounded by a non-magnetic material 1b having an M-0 bond, nitrogen will not be released from the film by heating. Therefore, it does not exhibit a Curie temperature that would cause a large change in saturation magnetization, but coercive force decreases with heating, so these phenomena can be used to heat with laser light and write by applying a magnetic field. It becomes a magneto-optical recording material that can be embedded.

Until now, the perpendicular magnetic anisotropy field (Hk) was, for example, 4K.
It was said that the maximum value was around Oe, but if a film structure like the magnetic thin film of the present invention is adopted, the saturation magnetization will be significantly reduced, and therefore the perpendicular magnetic anisotropy field (Hk) will be 4.
In particular, if the ratio of the ferromagnetic metal M (Fe, Co, Ni) component in IhN (2<x≦3) is increased, a value of 5KOe or more can be easily obtained.

The appropriate thickness of the magnetic thin film is 5,008 to 1 μs, preferably 100 to 3,000 μs. Various PVD and CVD methods may be used for film formation, and ion heat spanometry is particularly preferred.

It is recognized that the thermal stability of the magnetic thin film according to the present invention is further improved by employing the above configuration. The reasons for this are not necessarily clear, but (i) crystal growth is suppressed due to the presence of a nonmagnetic material with M-0 bonds, and (■) magnetostriction is reduced in highly oriented crystal parts. etc. are possible.

When using this magnetic thin film as a magneto-optical recording material, as mentioned earlier, if the magnetic thin film is repeatedly heated and cooled during recording, oxidation may progress even though it is relatively stable. . However, it was found that this oxidation does not proceed in a vacuum, and that oxidation does not proceed if a nonsivation film is further applied to the magnetic thin film. Therefore, it is desirable that this film (antioxidant film) has high transparency, high density, does not allow oxygen to pass through, and has good adhesion.For example, Tie, which is generally used as a film material, Ti
0N, AQSiO, TiN, AQS iN, BN,
SiN, AflN, A! LSiON, SiO
, S iON, 5i02. Advantageously, it is made of Cr5iN or the like.

Further, the film thickness of this material is suitably 100 Å to 100 OA, preferably 500 to 300 OA, and the film forming method includes, but is not limited to, the slat vine method, the vapor deposition method, the ion blating method, and the like.

In order to actually form the magnetic film according to the present invention, it is sufficient to form a magnetic thin film directly or via a reflective layer on a non-magnetic support, and further form an oxidation-preventing film thereon. The method for forming the magnetic thin film is as described above, and although air may be used as the introduced gas, CO□ gas may be used to optimize the total gas pressure of the ionized gases of N2 and A. By.

A desired membrane structure can be obtained.

The Fe, Co and/or Ni fine particles thus formed and the non-magnetic component having these metal (M)-oxygen bonds are combined into an E-phase MIN (2<1≦3, M: Fe, Co or Ni).
The columnar magnetic thin film has significantly improved heat resistance, is dense, has good friction and corrosion resistance, and is mechanically and chemically stable. Since the surface of the magnetic thin film is coated with an oxidation-preventing film, oxidation of the magnetic thin film due to heating is effectively prevented.

The non-magnetic support 3 is made of plastic film (heat-resistant plastic film such as polyimide, polyamide, polyethersulfone, polyethylene terephthalate, polyvinyl chloride, cellulose triacetate, polycarbonate, polymethyl methacrylate, etc.), ceramic, metal, glass. The shapes include, for example, film, tape, sheet, disk, cart, and drum shapes.

The reflective layer is Au, AQ, Ag, PL, CT, Nd,
The film is formed using materials such as Ge, Rh, Cu, and TiN by various evaporation methods such as electron beam (EB) evaporation, and thin film formation methods such as ion booting, sputtering, PVD, and CVD. The thickness of the reflective layer is preferably 1 .mu.s or less, preferably 0.05-0.5/j11<.

Note that a dielectric layer (a thin film of S102, TlO2, silicon nitride, aluminum nitride, amorphous 51, etc.) may be provided on the upper surface of the anti-oxidation film or the lower surface of the magnetic thin film to produce an enhancement effect.

〔Example〕

Next, Examples and Comparative Examples will be shown, but the magnetic film of the present invention is not limited to these Examples.

Example 1 After forming an Afl film with a thickness of about 150 OA on a polycarbonate disk substrate using a vacuum evaporation device, a magnetic thin film with a thickness of about 150 OA was formed on the second AQ pattern using an ion beam sputtering device under the following conditions. A film was formed.

Target material Fe (99,99%) Distance between target and substrate M15II 1m Substrate rotation speed 2+pm Back pressure of vacuum chamber I (75%) Introduced gas (pressure) Air (1 x 10" Torr) Total gas pressure during film formation 1.5
When examined by line diffraction method, E-phase FexN (2<X≦3)
Only peaks representing the (002) and (004) diffraction planes were observed. When the cross section was examined using the TEM method, the diameter was 25.
A columnar structure of OA was observed. When examining the female power spectrum, vertical alignment of α-Fe was observed.

When the EXAFS spectrum was examined, a spectrum similar to that of Fe3O4 was observed. Further, the magnetic properties examined by VSM were as follows. Hcyo (coercive force) = 69
00e, Hc4 (coercive force) = 2100e, Ms (saturation magnetization) = 570 emu/cc, sq□ (squareness ratio) = 0°26, Hk (perpendicular anisotropic magnetic field) -4,0 KOe perpendicularly magnetized film. Ta. The light transmittance was 51% (λ=800 nm).

Next, 5i was deposited on this magnetic thin film using a sputtering method.
An AflON film was provided. The film forming conditions were: discharge chamber cuff 00W;
Substrate rotation speed 15rprn, distance between substrate and target 7
0 mrn, flow rate ratio of N2 and Ar 1/9, N2 and A
r gas pressure IX 10-”Too+, target 5i
The AQ and film thickness were approximately 150OA. The light transmittance was 46%.

3. This magneto-optical recording medium. lim/5ec(C1,N)
Recording frequency 1.28M1-1z, playback power at a speed of
Recording and reproduction were performed under the conditions of mW (the laser beam was
(incident from the iAQON membrane side). As a result, the C/N was 26 dB. Then, after repeating recording and reproducing 100,000 times, the C/N was measured at 26 dB with no change.

Comparative Example S i A magneto-optical recording medium was produced in the same manner as in Example 1 except that the AnON film (antioxidation film) was omitted.
When I recorded and played back the same recording, I found that the early C.
/N=211 dB, but the C/N value decreased somewhat after 100,000 recording/playbacks.

〔Effect of the invention〕

The nitride magnetic thin film of the present invention has a perpendicular magnetic anisotropy field (Hk
) is large, but the ridges do not decompose or dissipate nitrogen, and the anti-oxidation film is effective against oxidation of the magnetic thin film due to heating; to prevent this, magneto-optical recording is used repeatedly. It is extremely advantageous for media applications.

Claims (1)

[Claims] (1) Fine particles of metal (M) selected from Fe, Co, and Ni formed directly or via a reflective layer on a nonmagnetic support, a nonmagnetic material having an M-O bond, and M_XN(2<
A transparent, non-magnetic oxidation-preventing film is not provided on the surface of a magnetic thin film having a columnar structure mainly composed of nitride of C-axis oriented crystals represented by X≦3) and having perpendicular magnetic anisotropy. A magnetic film characterized by