JPH03178105A - Thin garnet film for magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To realize the fining of crystal particles and the increase in coercive force while retaining a Faraday rotational angle on a low cost glass substrate by a method wherein a specific amount of Cu is added to an amorphous element contained in a garnet composition. CONSTITUTION:Cu at the atomic weight ratio of 2.0at%-5.0at% in the residual elements excluding oxygen is added to a film comprising BixR3-xMyFe5-yO12 in the basic composition (wherein R represents rare earth element including Y, M represents GaAl) with x and y meeting such requirements as 1.5<=x<=3.0, 0<=y<=2.0. At this time, Cu added to an amorphous element contained in the garnet composition accelerates the production of crystal nuclei while after the crystallization, works as a pinning site to obstruct the movement of mag netic wall. Through these procedures, the fining of crystal particles and the increase in coercive force can be realized simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a garnet thin film for a magneto-optical recording medium that reduces noise originating from grain boundaries in a garnet polycrystalline thin film and improves performance as a magneto-optical recording medium.

(Prior Art) Magneto-optical recording is attracting attention as the most promising technology for achieving high density and high reliability in rewritable optical memory. Amorphous rare earth-transition metals have already been realized as media, but this material contains rare earths that are easily oxidized, so the medium itself has low corrosion resistance, and has the disadvantages that the magneto-optic effect used during recording and reproduction is small. Garnet materials, which exhibit high corrosion resistance and a large magneto-optic effect at short wavelengths, are considered the most promising as next-generation magneto-optical media that can overcome the drawbacks of amorphous rare earth-transition metals. However, thin films formed on glass substrates by sputtering are polycrystalline, resulting in optical non-uniformity (non-uniform distribution of refractive index) and magnetic non-uniformity (non-uniform distribution of coercive force) originating from crystal grain boundaries. Therefore, the disadvantage is that the medium noise is large.

Recently, Gomi et al. added W to Dy-based garnet to increase the coercive force inside the crystal grains, and succeeded in making the distribution uniform and improving the film quality (Gomt et al: J, Appl.
.

Phys, + 63 (8), 3642 (1988
)), Ito et al. refined the crystal grains and improved optical uniformity by adding B (Ito et al.: 12th
Abstracts of the Annual Conference of the Japanese Society of Applied Magnetics, 127 (198
8)). However, depending on the added element, the crystal grain size ia
There are almost no reports that have simultaneously achieved microfabrication of less than m and a sufficient improvement in coercive force.

(Problems to be Solved by the Invention) The present invention overcomes the above-mentioned drawbacks of polycrystalline garnet thin films by simultaneously achieving finer crystal grains and imparting high coercive force using additive elements, thereby creating a high-performance magneto-optical recording medium. The purpose is to provide.

(Means for Solving the Problems) The present invention has a basic composition of BixRff-xMyFes-y.
o+z (here, R is a rare earth element including Y, M is Ga, A
The garnet thin film that satisfies 1.5≦x≦3.0 and O≦y≦2.0 (representing Z) has an atomic weight ratio of 2.0 at% or more of the remaining elements excluding oxygen5. The gist of the present invention is to provide a garnet thin film for a magneto-optical recording medium, which is characterized in that Cu is added in Oat% or less, the crystal grain size is 1- or less, and the coercive force estimated by a Faraday loop is 1 kOe or more.

(Function) The present inventors have investigated the effects of C added into an amorphous substance having a garnet composition.
It has been found that u promotes the generation of crystal nuclei and acts as a pinning site after crystallization to prevent domain wall movement, thereby achieving both crystal grain refinement and coercive force increase at the same time.

As a result, a large amount of Y or a rare earth element is replaced by the magneto-optic effect enhancing element Bi, and the magnetic transition temperature adjusting element G
The basic composition in which the Fe element is replaced with a, /V is BixR1-
JyFes-yo+z (where R is a rare earth element including Y, M is Ga, Aj) and 1.5≦x≦3.0 (atomic weight ratio of the remaining elements excluding oxygen is 18.8 at% or more3)
By adding Cu to a garnet thin film that satisfies 0≦y≦2.0 (at least 25.0at% in atomic weight ratio of the remaining elements excluding oxygen), the Faraday rotation angle It has now become possible to produce a polycrystalline thin film with a crystal grain size of 1 μm or less, a coercive force of 1 kOe or more, and good squareness without decreasing the crystal grain size. here,
Cu has an atomic weight ratio of 2.0% of the remaining elements excluding oxygen. Oat
% or more5. It is necessary to add in a range that satisfies Oat% or less. That is, if the Cu amount exceeds 5.0 at% or 2.0 at% is ungrooved, the crystal grain size becomes larger than IInn, and the squareness deteriorates. Moreover, the coercive force can also be controlled by the amount of Cu added.

Such a garnet polycrystalline thin film is first formed in an amorphous state on a glass substrate by high frequency or magnetron sputtering. Ar gas or a mixed gas of Ar and oxygen may be used for sputtering, and substrate heating and bias voltage may be applied. As a method for adding Cu, a sintered target containing all the bones may be used, or a Cu metal or oxide chip may be placed on a target that does not contain Cu. If an amorphous film is heat-treated at high temperature, a different phase may precipitate, so it is crystallized at a temperature above the crystallization temperature and below the crystallization temperature +100"C. The crystallization temperature of Bi-substituted garnet mainly depends on the amount of Bi. However, in the present invention, 500
~650°C.

(Example) Examples of the present invention will be described below with reference to the drawings.

Example 1 (BiGa-substituted Dy iron garnet) BizD
3/+Ga+Fe40+z (Atomic weight ratio of remaining elements excluding oxygen: Bi is 25.0at%, Dy is 12.5
at%, Ga is 12.5 at% and Fe is 50, Oa
t%) and a garnet thin film having a composition of
A garnet thin film doped with u was formed using a high frequency sputtering device. For example, the bottom film is prepared under an Ar gas pressure of 30 mTo.
rr, performed on a glass substrate at a radio frequency power of 200W. As a Cu addition method, metal C is added onto a sintered target.
A bottom film was formed by placing a u-chip, and the amount of Cu was adjusted by changing the area of the Cu chip. The film thickness is about 0.9-. Table 1 shows the composition of Targetera 1411 and the sputtered film. Here, component analysis was performed by inductively coupled plasma emission spectrometry (ICP).

FIG. 1 shows transmission optical micrographs of a 3.4 at % Cu-added film (a) and a non-additive film) formed as bottom films under the same sputtering conditions and subjected to the same heat treatment. Here, the heat treatment was carried out in the atmosphere at 620"C for 3 hours. With the addition of Cu, the particle size became 1- or less, which is about 115 or less than that without additives. In Figure 2,
A similar comparison of coercive force and squareness is shown using a Faraday loop at a wavelength of 633 nm. Cu3.4
The at% doped film (Fig. 2 (a)) maintains a large rotation angle (2.2°/-) compared to the Cu-free film (Fig. 2 (b)) and has a large coercive force of 5.5 kOe. It can be seen that this shows a loop with good squareness. Figure 3 shows Cu8. Oat%
A transmission optical micrograph (a) of the additive film and a Faraday loop (b) at a wavelength of 633 nm of the Cu 1.6% additive film are shown. Cu amount is 5. When the Oat% was exceeded or 2.0at% was not grooved, the crystal grain size became larger than 1n, and the squareness of the Faraday loop also decreased.

Example 2 (BiA7-substituted Y-substituted iron garnet B1
(Ga-substituted Gd-iron garnet) Table 2 shows the results of the addition of Cu in the BiAJ-substituted Y-iron garnet and Ga-substituted Gd-iron garnet thin films. Similar to Example 1, grain size of 1- or less and 1 k
A coercive force greater than oe was obtained.

Table 2 θ, Faraday rotation angle Hc at two wavelengths of 633 nm: Coercive force (effect of the invention) As explained above in the examples, a large Faraday rotation angle can be maintained on an inexpensive glass substrate by adding Cu. However, it has become possible to produce a garnet polycrystalline thin film that exhibits a crystal grain size of - or less, a coercive force of 1 kOe or more, and very good Faraday loop squareness. Such a Garnet 7m film is promising as a magneto-optical recording medium.

[Brief explanation of drawings]

Figure 1 shows (a) Cu3.4 at% addition and (b) C
Transmission optical micrograph (magnification: 1000) of the crystal structure of a B1Ga-substituted Dy iron garnet thin film without u additives, Figure 2 is (
Wavelength 633 nm of a) Cu 3.4 a t% addition and (b) Cu-free B1Ga substituted Dy iron garnet thin film
The Faraday loop in Figure 3(a) is Cu8. O
Transmission optical micrograph (magnification 1000) of crystal structure of at% added B1Ga-substituted DY iron garnet thin film, same <(
b) is a diagram showing a Faraday loop at a wavelength of 633 nm in a B1Ga-substituted Dy iron garnet thin film added with 1.6 at% of Cu. Figure 1 (0,) (b) Figure 2 (a) (b)

Claims (4)

[Claims] (1) Basic composition is Bi_xR_3_-_xM_yFe_
5_-_yO_1_2 (here, R is a rare earth element containing Y, M represents Ga, Al), 1.5≦x≦3.0, 0≦
A garnet thin film for a magneto-optical recording medium, characterized in that Cu is added in an atomic weight ratio of 2.0 at% to 5.0 at% of the remaining elements excluding oxygen to a garnet thin film satisfying y≦2.0. (2) The garnet thin film for a magneto-optical recording medium according to claim 1, comprising fine polycrystals with a crystal grain size of 1 μm or less. (3) The garnet thin film for a magneto-optical recording medium according to claim 1, which has a coercive force of 1 kOe or more. (4) Consisting of fine polycrystals with a crystal grain size of 1 μm or less,
The garnet thin film for a magneto-optical recording medium according to claim 1, which has a coercive force of 1 kOe or more.