JPH0464940A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To reduce the exchange coupling force with good reproducibility by forming a magneto-optical recording layer having a specified relation between the Curie temp. and coercive force at room temp., and providing a nitrogen- contg. area of specified thickness containing a specified amt. of nitrogen near the interface between the magneto-optical recording layer and an auxiliary recording layer. CONSTITUTION:A rewritable magneto-optical recording medium is obtained by successively forming a magneto-optical recording layer and an auxiliary recording layer on a substrate in a manner that the Curie temp. Tc1 and coercive force Hc1 at room temp. of the magneto-optical recording layer and the Curie temp. Tc2 and coercive force Hc2 at room temp. of the auxiliary recording layer satisfy the relation Tc1<Tc2 and Hc1>Hc2. In this structure, a nitrogen- contg. area is provided near the interface between the magneto-optical recording layer and the auxiliary recording layer so that the nitrogen-contg. area is made between >=20Angstrom and <=100Angstrom thick and contains >=10 atomic % nitrogen and that the maximum nitrogen content in this area is <=30 atomic %.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording medium capable of optical recording and reproduction.

[Conventional technology and its issues]

Magneto-optical recording media are being put into practical use as high-density, low-cost, rewritable information recording media. In particular, media using recording layers of amorphous alloys of rare earths and transition metals have shown very excellent characteristics.

A major drawback of magneto-optical recording media is that they cannot be overwritten. That is,
Conventional magneto-optical recording media require an erasing process before recording, requiring two rotations for one recording, reducing data transfer speed.

In recent years, some methods have been proposed to perform this overwriting in magneto-optical recording media. A promising method is the optical modulation override method using a multilayer film.

This method is the 34th Applied Physics Association Conference Proceedings 2
8P-ZL-3P721 (1987), which includes a perpendicular magnetization layer (magneto-optical recording layer) with a low Curie temperature and high coercivity, and a relatively high Curie temperature and low coercivity with respect to the recording layer. It consists of a perpendicularly magnetized layer (recording auxiliary layer) with a strong magnetic field.

The overriding method is to first apply an initializing magnetic field (Hint) of a magnitude sufficient to align the direction of magnetization of the recording auxiliary layer and not to affect the magneto-optical recording layer, and then to apply a high initialization magnetic field (Hint) while applying a bias magnetic field. A light beam modulated into two values of power (po) and low power (pt) is irradiated. During PL irradiation, there is no reversal of the recording auxiliary layer, and the magneto-optical recording layer is stabilized by exchange coupling with the recording auxiliary layer, and in the case of P□ irradiation, the recording auxiliary layer is reversed by the bias magnetic field (Hb). , and the magneto-optical recording layer also faces in the opposite direction to the PL case, thereby making override possible.

It is desirable that the Hini be as small as possible in terms of cost reduction and miniaturization of the drive.

Hint can be made smaller as the exchange coupling force between the magneto-optical recording layer and the recording auxiliary layer becomes smaller.

If the exchange coupling force is too small, overriding itself becomes impossible, so it is necessary to adjust it to an appropriate size.

As a method for appropriately reducing the exchange coupling force, a method has been proposed in which an intermediate magnetic layer (such as GdFeCo) having a small perpendicular magnetic anisotropy is inserted between the magneto-optical recording layer and the recording auxiliary layer.

However, since this method requires three different magnetic layers, it requires a large film forming apparatus and has the disadvantage of increasing target cost. Moreover, since there is an interface between two magnetic layers above and below the intermediate magnetic layer, the interface is easily affected by oxidation, etc., making it difficult to produce a disk with good reproducibility. Therefore, a method for reducing the exchange coupling force at low cost and with good reproducibility has been desired.

[Means to solve problems]

As a result of the inventors' studies regarding the above problems,
It has been found that the exchange coupling force can be reduced at low cost and with good reproducibility by providing a nitrogen-containing layer near the interface between the magneto-optical recording layer and the recording auxiliary layer.

[Structure of the invention]

The gist of the present invention is that a magneto-optical recording layer having a Curie temperature Tc1 and a coercive force Hc at room temperature and a recording auxiliary layer having a Curie temperature Tcz and a coercive force Hc2 at room temperature are laminated in this order on a substrate, Said Tc + + T c 2+
Hc 1+ Hc 2 is Tc+ <Tcz, HC+
>In an overwritable magneto-optical recording medium that satisfies HC2, a region containing 10 atomic % or more of nitrogen exists near the interface between the magneto-optical recording layer and the recording auxiliary layer with a thickness of 20 Å or more and 100 Å or less, and The maximum nitrogen content in the area is 30
% or less.

The present invention will be explained in detail below.

Examples of the substrate used in the present invention include transparent substrates such as glass and plastics such as acrylic resin and polycarbonate resin. The thickness of the substrate is generally about 1.2 mm.

In the present invention, a magneto-optical recording layer and a recording auxiliary layer are provided on a substrate. As a magneto-optical recording layer, the relative Curie temperature Tc,
A material with a low holding force Hc and a large holding force Hc is used. For example, TbFe, TbFeCo.

Examples include DyFe, DyFeCo, TbDyFeCo, and the like. Tc+ is preferably 120°C or more and 200°C or less, and Hc is preferably 10 koe or more. The film thickness is preferably about 300 to 1000 people.

As the recording auxiliary layer, one having a relatively high Curie temperature Tc2 and a coercive force Hcz smaller than Hc is used.

For example, TbFeCo, DyFeCo, DyCo, TbD
yFeCo, TbCo, GdDyFe, GdDyFeC
o, GdTbFe.

Examples include GdTbFeCo. 18 as Tcz
Of course, Tc is preferably 0°C or higher and 250°C or lower.
Needs to be bigger. Furthermore, a smaller Hcz is preferable in order to reduce the initialization magnetic field (Hi n i ), but the recording auxiliary layer receives an effective bias magnetic field (Hw) due to exchange coupling with the magneto-optical recording layer. In order to maintain a stable state of
is necessary.

Hcz is generally preferably about 1 kOe or more and 3 koe or less.

The thickness of the recording auxiliary layer is preferably 500 Å or more and 2500 Å or less.

In the present invention, a nitrogen-containing region is provided near the interface between the recording layer and the auxiliary layer. In order to contain nitrogen, for example, there is a method of introducing nitrogen gas during film formation near the interface of the recording layer or the auxiliary layer.

In the nitrogen-containing region, the perpendicular magnetic anisotropy decreases but is not completely lost, so it has characteristics suitable for appropriately reducing the exchange coupling force.

A decrease in perpendicular magnetic anisotropy occurs even when oxygen is used instead of nitrogen, but oxygen reacts violently with the magnetic layer, and even a small amount of oxygen reduces Hw to almost zero, making override itself impossible. become. Nitrogen, which is appropriately reactive with the magnetic layer, is suitable as an additive element. Furthermore, since the nitrogen-containing region has lower reactivity with oxygen than in the case where it does not contain nitrogen, it is not affected by residual oxygen or moisture in the chamber, and the reproducibility of characteristics is extremely excellent.

The content of nitrogen and the width of the containing region are defined within a range that can sufficiently reduce the exchange bonding force and maintain the override phenomenon, and the region containing 10 atomic % or more is 20 Å or more, 10
It is 0 Å or less. Further, the maximum content of nitrogen in this region is 30 atomic % or less. The nitrogen-containing region may be present in one of the layers or may span both layers. The width of the nitrogen-containing region is 10 Å or more
Å or less is preferable.

After forming the recording auxiliary layer, a protective layer may be provided to prevent oxidation of the magnetic layer. As a protective layer, S 13Na,
AIN, Taz05. Stable dielectrics such as AnzOz and TiO2 are preferably used.

The thickness of the protective layer is preferably about 500 to 2000.

An interference layer may be provided between the substrate and the magneto-optical recording layer. The interference layer is Si3N4. AffN, Ta2es.

A transparent dielectric material such as A 42 z Oz or T 102 is used. The purpose of the interference layer is to lower the reflectance through the interference effect, improving sensitivity and reducing noise.The thickness of the layer is determined by the refractive index of the interference layer, but it is usually 5.
C10~1500 people are used.

Physical vapor deposition (PVD) such as sputtering, chemical vapor deposition (CCVD) such as plasma CVD, etc. are applied to the method of forming each layer on the substrate.

To form a magneto-optical recording layer, a reflective layer, and a protective layer using the PVD method, the usual method is to deposit each layer on a substrate by electron beam evaporation or sputtering using a target with a predetermined composition. It is.

Furthermore, a method using ion blating is also considered.

If the film deposition rate is too fast, it will increase the film stress, and if it is too slow, it will affect productivity, so it is usually 0.1 person/Sec to 100.
It is said to be about 1 person/sec.

〔Example〕

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Examples 1 to 3, Comparative Examples 1 to 4 A 130 mmΦ polycarbonate substrate was introduced into a sputtering apparatus having two film formation chambers, and first 3X
The atmosphere was evacuated to 10-7 Torr or less, and a Ta target was reactively sputtered using a mixed gas of Ar and 0□ to form an interference layer of 800 Tazos.

After moving the substrate to another chamber with a vacuum level of 2 X 10-7 Torr or less, Ar was heated at 10100C, 4 m
Tb and FeqsCOs (
At the same time, sputtering is performed on a target of less than atomic %, and T b+q (F eqsCO5) e+
A recording layer was formed. When the thickness of the recording layer reached 500 layers, nitrogen gas was introduced to form a nitrogen-containing region to a predetermined thickness. The nitrogen content was adjusted by changing the nitrogen gas flow rate.

After stopping the nitrogen gas, simultaneous sputtering of Dy and Fe-toCo3° targets was performed, and D)'3Q(F
e7. Co3. ) 7. An auxiliary layer with a composition of 1
500 people were formed.

After returning the substrate to the initial chamber, T a 20 s
A protective layer of 800 people was formed.

Table 1 shows the override characteristics of the disk thus prepared, the maximum nitrogen content in the nitrogen-containing region, and the region width (region where the nitrogen content exceeds 10 atom %). The override characteristic is a linear velocity of 5.6 m/s.

Pt = 4mJ P, -9mW, Hb = 2000
3.7 MHz on a 1.4 MHz signal under e conditions
signal was overridden. The nitrogen content was analyzed using Auger electron spectroscopy while etching with Ar ions.

As a result, disks with suitable nitrogen-containing regions have low H
It was possible to override with int.

Example 4 The structure was similar to Examples 1 to 3, but nitrogen gas was not flowed when forming the recording layer, but nitrogen gas was introduced from the start of forming the auxiliary layer until a predetermined film thickness was reached, and then nitrogen gas was introduced. The gas supply was stopped and the auxiliary layer was deposited until the number of people reached 1,500.

Examples 1 to 3 show the override characteristics, nitrogen content in the nitrogen-containing region, and region width of the disk thus created.
It was measured in the same manner.

As a result, similar to the case where the recording layer contains nitrogen,
Override was possible at low Hini.

〔Effect of the invention〕

The magneto-optical recording medium of the present invention can be overridden, can reduce exchange coupling force with good reproducibility, and can be manufactured at low cost.

Claims (1)

[Claims] (1) A magneto-optical recording layer with a Curie temperature Tc_1 and a coercivity Hc_1 at room temperature on a substrate, and a Curie temperature T
c_2, a recording auxiliary layer having a coercive force Hc_2 at room temperature is laminated in this order, and the Tc_1, Tc_2, Hc_1
, Hc_2 satisfies Tc_1<Tc_2, Hc_1>Hc_2 in an overwritable magneto-optical recording medium, in which 10 atomic % of nitrogen is added near the interface between the magneto-optical recording layer and the recording auxiliary layer.
A magneto-optical recording medium characterized in that a region containing the above-mentioned nitrogen exists with a thickness of 20 Å or more and 100 Å or less, and the maximum nitrogen content of the region is 30 atomic % or less.