JPH04281239A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide the magneto-optical recording medium which can execute good magnetic field modulation recording even under a low magnetic field. CONSTITUTION:The magnetic layer 3 of the magneto-optical recording medium formed by laminating a 1st dielectric layer 2, a magnetic layer 3, a 2nd dielectric layer 4, and a reflection film 5 in this order on a substrate 1 consists of a 1st rare earth/transition metal alloy film 3a contg. Gd, Fe and Co and a 2nd rare earth/transition metal alloy film 3b contg. Tb, Fe and Co. The overall thickness of the above-mentioned magnetic layer 3 is 200 to 300Angstrom and the film thickness of the above-mentioned 1st rare earth/transition metal alloy film 3a with respect to the total thickness of this magnetic layer 3 is limited to 20 to 50%.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for recording and reproducing information using the magneto-optic effect.

0002

[Background Art] In recent years, as a rewritable high-density recording method, a magneto-optical method has been developed in which information is recorded by writing magnetic domains in a magnetic thin film using thermal energy such as semiconductor laser light, and this information is read out using the magneto-optic effect. The recording method is attracting attention.

The recording materials used in this magneto-optical recording system include rare earth elements such as Gd, Tb, and Dy, as well as Fe and C.
Amorphous alloy film (hereinafter referred to as
It is called RE-TM film. ) is a typical example. This RE-TM film has large perpendicular magnetic anisotropy energy, so it can easily be used as a perpendicular magnetization film necessary for high-density recording, it is amorphous, so medium noise is small, and the Kerr rotation angle is relatively large. It has many advantages, such as a low Curie point and the ability to record and erase with a commercially available semiconductor laser (20 to 40 mW). For example, Tokuhei 2-3
As disclosed in Japanese Patent No. 2690, it is known that a GdTbFeCo film containing Tb or Gd as a rare earth element has a particularly large Kerr rotation angle and can obtain a good S/N ratio.

On the other hand, the above-mentioned magneto-optical recording method includes an optical modulation method in which a direct current external magnetic field is always applied and laser light is irradiated depending on the presence or absence of a signal. This optical modulation method has been studied from an early stage because the device configuration is relatively simple. However, with this optical modulation method, overwriting is not possible when re-recording an already recorded part, and an erasing operation is required to align the direction of magnetization in a certain direction. However, it has the disadvantage that the effective data transfer rate is slow.

On the other hand, the magnetic field modulation method, which always irradiates a laser beam with a constant intensity and reverses the external magnetic field depending on the presence or absence of a signal, allows overwriting and has a high speed comparable to that of a computer hard disk. It is now possible to record
There are also great expectations for practical use. In this magnetic field modulation method,
Compared to normal magnetic recording, the spacing between the disk medium surface and the head can be increased by more than an order of magnitude because there is no need to constrict the magnetic field to a small size; The effective recording magnetic field becomes weaker as the magnetic field increases. Therefore, it is strongly desired that the medium be capable of good magnetic field modulation recording even in a weak magnetic field.

Furthermore, when performing magnetic field modulation at a frequency of several MHz or higher, impedance increases due to the inductance L of the coil. Therefore, in order to obtain the desired magnetic field and current, a powerful power source, such as one with a very high voltage, is required, and an increase in power consumption is avoided. Further, due to the inductance L, the current waveform does not become an ideal rectangular wave, and a certain amount of switching time is required. In such a case, if the recording laser beam is continuously irradiated onto the medium, the magnetic field will be small or zero during switching, which will increase recording noise.
A good SN ratio cannot be obtained.

[0007] Therefore, it has been proposed to solve this problem by irradiating recording laser light not continuously but in pulses. If pulsed laser light is irradiated, the temperature of the medium will be lower than the Curie point when the magnetic field is in a switching state, and a sufficient magnetic field will be applied while the temperature of the medium is above the Curie point due to laser irradiation. It is possible to achieve this state. However, in this case, a sufficient magnetic field must be applied within the time period from when the temperature of the medium reaches the Curie point upon irradiation with the laser beam until it cools down to below the Curie point. Therefore, the medium is required to be sufficiently fast with respect to the thermal response of recording, that is, the change in the magnetic field modulating the time until the recorded magnetic domain is fixed.

[0008] In view of these requirements, the structure of a magneto-optical recording medium used in the magnetic field modulation method has conventionally been such that a first dielectric layer, a magnetic layer, and a second dielectric layer are formed on one main surface of a transparent substrate. It has a multilayer structure in which reflective films are sequentially laminated. In such a structure, the magnetic layer is made of, for example, TbFeCo.
It is made of a RE-TM film such as a film, and is desired to have a thin layer thickness for the purpose of increasing the cooling rate. Furthermore, in order to increase the signal level of the reproduced signal, considering the sensitivity to recording power and the effect of Kerr enhancement, the thickness of the magnetic layer is such that the wavelength of the recording laser beam is 780 nm.
It is desired that the thickness be about 200 to 300 Å when the thickness is around 500 nm, and about 150 to 220 Å when the thickness is around 500 nm. Further, as the reflective film, a material having a high reflectance in order to increase the signal amount and a high thermal conductivity in order to quickly absorb the heat of the magnetic layer is suitable, such as Al.
, Cu, Ag, Au, etc. are used.

[0009]

[Problems to be Solved by the Invention] In order to miniaturize the electromagnet used in the above-mentioned magneto-optical recording medium and to easily perform overwriting using a magnetic field modulation method, it is necessary to reduce the magnetic field necessary for recording. It is required to reduce it. In general, the factors that determine the external magnetic field include demagnetizing field,
These include stray magnetic fields, Bloch domain wall energy, coercive force and magnetization of the medium at the Curie temperature, etc., but reducing demagnetizing fields and stray magnetic fields is particularly effective in reducing external magnetic fields (for example, Japanese Patent Application Laid-Open No. 63-200343 (Refer to the publication.)

However, as mentioned above, if the thickness of the magnetic layer is 30
When the thickness is 0 Å or less, the contribution of demagnetizing fields and stray magnetic fields decreases, and the distribution of domain wall energy, coercive force, and magnetization caused by microstructural unevenness of the films that make up the magnetic layer suppresses the magnetic field necessary for recording. It becomes a deciding factor. For example, when the film structure is columnar and its diameter is 500 Å or less, the film behaves as fine particles, and when the film is thin, the volume of the particles decreases. Then, energy related to magnetization, for example Zeeman energy EZ [Ez = (magnetization) x (external magnetic field) x (volume of particle)], is thermal energy kB T (kB
is the Boltzmann constant and T is the absolute temperature). Therefore, the probability that the magnetization will be oriented in the direction of the external magnetic field decreases, and a large magnetic field will be required for recording.

[0011] In order to solve this problem, the above film must be formed uniformly, for example by heating the substrate or by etching the surface of the first dielectric layer formed on the substrate to make it smooth. This is not desirable from a practical point of view, as it requires additional steps. Alternatively, by lowering the perpendicular magnetic anisotropy of the film (for example, adding non-magnetic impurities to the TbFeCo film, or substituting or substituting Tb with Gd, Dy, Nd, etc.), There is a method of increasing the minimum stable magnetic domain diameter r.

[Math 1]

(However, in Equation 1, σB is the Bloch domain wall energy density, MS is the magnetization, HC is the coercive force, and KU
represent the perpendicular magnetic anisotropy energy, respectively. ) With this method, if a minute region is turned in the opposite direction to the external magnetic field due to some unevenness, if the diameter of that part is smaller than the above minimum stable magnetic domain diameter r, that part will disappear,
Point in the direction of the external magnetic field. Therefore, it is considered that the magnetic field required for recording can be reduced. However, if the minimum stable magnetic domain diameter r is increased, the stability of the minute magnetic domains deteriorates, resulting in an increase in recording noise and reproduction jitter. Therefore, in any case, with conventional magneto-optical recording media, it is difficult to reduce the external magnetic field. SUMMARY OF THE INVENTION The present invention has been proposed in view of the above-mentioned conventional situation, and an object of the present invention is to provide a magneto-optical recording medium that can reduce the magnetic field and perform magnetic field modulation recording satisfactorily even under a weak magnetic field. With the goal.

[0013]

SUMMARY OF THE INVENTION The present invention has been proposed to achieve the above objects. That is, the present invention provides a magneto-optical recording medium in which a first dielectric layer, a magnetic layer, a second dielectric layer, and a reflective film are laminated in this order on a substrate, in which the magnetic layer is made of Gd, Fe, and Co. and a second rare earth-transition metal alloy film containing Tb, Fe, and Co, the total thickness of the magnetic layer is 200 to 300 Å, and the first The thickness of the rare earth-transition metal alloy film is 20 to 20% of the total thickness of the above magnetic layer.
50%.

In the magneto-optical recording medium of the present invention, the magnetic layer is composed of a first rare earth-transition metal alloy film and a second rare earth-transition metal alloy film. The constituent materials of the first rare earth-transition metal alloy film are mainly Gd, which is a rare earth element, and Fe and Co, which are transition metals.
, Pt, Nd, Sm, etc. are used in small amounts. The first rare earth-transition metal alloy film made of such a magnetic material has a relatively small coercive force HC1 and perpendicular magnetic anisotropy KU1. Therefore, the minimum stable magnetic domain diameter r of the first rare earth-transition metal alloy film increases, which is effective in reducing the magnetic field required for recording. The thickness of this first rare earth-transition metal alloy film is preferably 50 to 100 Å.

The constituent materials of the second rare earth-transition metal alloy film include Tb, which is a rare earth element, and Fe, which is a transition metal.
, Co, and small amounts of additional elements such as Cr, Al, Pt, and Dy are also used. The second rare earth-transition metal alloy film composed of such a magnetic material has a relatively large coercive force HC2 (HC2>HC1) and perpendicular magnetic anisotropy KU2 (KU2>KU1), and has a microscopic It is possible to ensure the stability of magnetic domains and prevent recording noise. This second rare earth-transition metal alloy film is magnetically coupled to the first rare earth-transition metal alloy film through exchange coupling.

The total thickness of such a magnetic layer is between 200 and 30 mm.
It is assumed to be 0 Å. The thickness of the first rare earth-transition metal alloy film is 20 to 50% of the total thickness of the magnetic layer. If the thickness ratio of the first rare earth-transition metal alloy film is smaller than the above range, it will not be possible to sufficiently reduce the external magnetic field, and if it is larger than the above range, recording noise will increase. The dependence of the recording magnetic domain size on the external magnetic field becomes stronger, and there is a risk that unerased areas may occur during overwriting. The first rare earth-transition metal alloy film and the second rare earth-transition metal alloy film can be formed on the substrate by a vacuum thin film forming technique such as sputtering, molecular beam epitaxy, or vacuum evaporation. Note that either the first rare earth-transition metal alloy film or the second rare earth-transition metal alloy film may be formed first with respect to the light incident direction.

Materials for the substrate include glass, polycarbonate, PMMA (polymethyl methacrylate), ceramics, silicon wafer, or glass 2P (a photocurable resin layer having irregularities such as groups and pits formed on a glass substrate by photopolymerization). (formed substrates) etc. can be used. The first dielectric layer and the second dielectric layer are provided for the purpose of improving corrosion resistance and increasing the Kerr rotation angle due to multiple reflections (Kerr effect enhancement), and are made of oxides, nitrides, Materials such as oxynitride are obtained by vacuum thin film formation technology. Specific examples include Si3 N4, SiO, SiO2, AlN, Zn
S etc.

Further, the reflective film is provided to increase the rotation angle by reflecting the laser light transmitted through the magnetic layer and each dielectric layer, thereby adding the Faraday effect to the Kerr effect. Usually Al, Cu, Ag,
It is obtained by forming a film of a metal material such as Au using vacuum thin film formation technology. Writing methods for such magneto-optical recording media include, in addition to light beams, needle-shaped magnetic heads,
Needless to say, any device can be used as long as it can supply the energy necessary to generate reversed magnetic domains, such as a hot pen or an electron beam.

[0019]

[Operation] In the magneto-optical recording medium of the present invention, the magnetic layer has G
The first rare earth-transition metal alloy film containing Tb, Fe, and Co and the second rare earth-transition metal alloy film containing Tb, Fe, and Co are stacked. In such a magnetic layer, the first rare earth-transition metal alloy film has a relatively small coercive force HC1 and perpendicular magnetic anisotropy KU1, and the second rare earth-transition metal alloy film has a relatively large coercive force HC2. and perpendicular magnetic anisotropy KU2.

Here, the Curie point TC1 of the first rare earth-transition metal alloy film is set higher than the Curie point TC2 of the second rare earth-transition metal alloy film, and the laser beam is irradiated onto the magnetic layer. When the medium temperature becomes higher than TC1, the first rare earth-transition metal alloy film and the second rare earth-
The magnetization of the transition metal alloy film disappears, and the medium temperature T decreases by cooling.
When the value becomes TC1 or less, magnetization appears in the first rare earth-transition metal alloy film. At this time, even if a small region of the first rare earth-transition metal alloy film faces in the opposite direction to the external magnetic field, the coercive force HC1 of the first rare earth-transition metal alloy film is small, that is, the minimum stable magnetic domain diameter r is large. Therefore, the minute area mentioned above disappears. Therefore, the recording area of the first rare earth-transition metal alloy film is clearly oriented in the direction of the external magnetic field.

Thereafter, when the medium temperature T becomes lower than TC2 by further cooling, magnetization appears in the second rare earth-transition metal alloy film, but this direction is the exchange coupling direction with the first rare earth-transition metal alloy film. That is, for example, the iron group spins are aligned in the same direction. In this case, the boundary of the recording magnetic domain is TC2
Since the second rare earth-transition metal alloy film has a large perpendicular magnetic anisotropy KU2, its boundary is clear and recording noise is suppressed. Therefore, the first
The second rare earth-transition metal alloy film reduces the external magnetic field, and the second rare earth-transition metal alloy film prevents recording noise, making it possible to perform magnetic field modulation recording well even under weak magnetic fields. becomes.

[0022]

EXAMPLES Preferred examples of the present invention will be described below based on experimental results. Example 1 In this example, a first dielectric layer as a recording layer, a GeFeCoCr film which is a first RE-TM film, a first R
This is an example of a magneto-optical disk in which an E-TM film of TbFeCoCr, a second dielectric layer, and a reflective film are sequentially formed. First, Example 1 shows a schematic structure of the magneto-optical recording medium manufactured in this example.

This magneto-optical recording medium is intended to be used for recording and reproducing, and one main component of this magneto-optical recording medium is a transparent substrate 1 made of polycarbonate in which guide grooves (not shown) are formed with a pitch width of 1.6 μm. First, Si3 N4 is applied on surface 1a.
A first dielectric layer 2 is formed. This first
The film thickness of the dielectric layer 2 is 1100 Å.

A magnetic layer 3 for retaining information is provided on the first dielectric layer 2. This magnetic layer 3 is made of GeFeC
It consists of a two-layer film in which an oCr film 3a and a TbFeCoCr film 3b are sequentially laminated, and the total layer thickness is 250 Å. On this magnetic layer 3, a second dielectric layer 4 made of a Si3N4 film with a film thickness of 450 Å is formed, and on this second dielectric layer 4, an Al reflective film 5 with a thickness of 500 Å and an ultraviolet curing resin are formed. Protective films 6 are sequentially laminated.

[0025] Such a magneto-optical disk was manufactured as follows. First, the first dielectric layer 2, GeFeC
Since the oCr film 3a, the TbFeCoCr film 3b, the second dielectric layer 4 and the Al reflective film 5 are formed in a continuous process,
Si, Gd, Fe in the chamber of the sputtering equipment
80Co10Cr10 alloy (numbers represent atomic percent),
Each target of Tb and Al was mounted. According to this sputtering apparatus, a desired film can be formed by opening and closing shutters provided corresponding to each target.

Then, the substrate 1 is mounted on the substrate holder,
After evacuating the chamber and adjusting the degree of vacuum to a predetermined degree, a sputtering gas containing nitrogen gas is introduced, and reactive sputtering is performed using Si as a target in an atmosphere having a predetermined gas pressure. Body layer 2 was formed. Next, GeFe was deposited by direct current magnetron sputtering.
A CoCr film 3a and a TbFeCoCr film 3b were sequentially formed. Note that the GeFeCoCr film 3a was formed using Gd
For forming the TbFeCoCr film 3b, Tb and FeCoCr alloys were used as targets, respectively.

Next, reactive sputtering is performed again using a Si target to form a second dielectric layer 2.
Furthermore, an Al reflective film 5 was formed by sputtering using an Al target. Finally, a protective film 6 was formed by coating the surface of the Al reflective film 5 with an ultraviolet curing resin, thereby completing a magneto-optical disk.

Each R film formed on the substrate 1 in this way
The magneto-optical properties of the E-TM film are first determined by the above-mentioned GeFeCoC.
The coercive force HC1 of the r film 3a is 100 Oe (iron group rich composition) at room temperature, and the perpendicular magnetic anisotropy KU1 is approximately 2×105 e
rg/cm3. On the other hand, TbFeCoCr film 3b
has a composition near the compensation composition where the coercive force HC2 is 10 KOe or more at room temperature, and the perpendicular magnetic anisotropy KU2 is 2×106
erg/cm3. Therefore, coercive force HC2 and perpendicular magnetic anisotropy KU2 are larger than coercive force HC1 and perpendicular magnetic anisotropy KU1. Further, the Curie point TC1 of the GeFeCoCr film 3a is 240°C, and the TbFeCoCr film 3a has a Curie point TC1 of 240°C.
The Curie point TC2 of the oCr film 3b is 183°C, and G
The eFeCoCr film 3a is set to have a higher Curie point.

Recording was performed on such a magneto-optical disk using the magnetic field modulation method, and the output characteristics were examined. During recording, the magnetic field was applied by a flying head, the switching time was about 20 ns, and the recording frequency was 5 MHz. Laser irradiation was performed using a laser pulse (10 MHz) with a pulse width of 30 ns. At this time, the influence of the switching region can be ignored. Also, the linear velocity is 1
0m/sec, playback power 2.5mW, recording power 18
It was set as mW.

FIG. 2 shows GeFeCoCr constituting the magnetic layer.
FIG. 3 is a diagram showing the results of investigating the relationship between the magnitude of the external magnetic field during recording and the CN ratio for three types of magneto-optical disks (referred to as Examples 1 to 3, respectively) with different film thickness ratios between the film and the TbFeCoCr film. . In Example 1, the thickness d1 of the GeFeCoCr film is 60 Å, and the thickness d2 of the TbFeCoCr film is 190 Å. In Example 2, d1 is 100 Å, d
2 is 150 Å, in Example 3, d1 is 150 Å.
This is the case where Å, d2 is 100 Å. For comparison, FIG.
Also shown inside. However, in Comparative Example 2, GeFe
The perpendicular magnetic anisotropy of the CoCr film is 1×106 erg/c
m3, and the recording power was 23 mW.

As shown in FIG. 2, in Examples 1 to 3, the CN ratio hardly decreased even when the external magnetic field was about 75 Oe. From this fact, the magnetic layer is made of GeFeCoC.
It was found that by using a two-layer structure of an r film and a TbFeCoCr film, good magnetic field modulation recording could be performed with little recording noise even under a weak magnetic field. Moreover, compared to Examples 1 and 2, in Example 3 where the film thickness ratio of the GeFeCoCr film is large, the CN ratio becomes smaller. Therefore, when the total thickness of the magnetic layer is 250 Å, it is preferable that the thickness of the GeFeCoCr film is 100 Å or less.

[0032]

Effects of the Invention As is clear from the above description, in the magneto-optical recording medium of the present invention, the magnetic layer is composed of a first rare earth-transition metal alloy film and a second rare earth-transition metal alloy film. Therefore, even if the external magnetic field is reduced, recording noise can be prevented and a sufficient CN ratio can be ensured. Therefore, the present invention can provide a magneto-optical recording medium having an overwrite function that allows good magnetic field modulation recording even under a weak magnetic field.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of an example of a magneto-optical recording medium to which the present invention is applied.

FIG. 2 is a characteristic diagram showing the relationship between the magnitude of an external magnetic field and the CN ratio during recording of magneto-optical recording media with different thickness ratios of GeFeCoCr films and TbFeCoCr films.

[Explanation of symbols]

1... Board 2...First dielectric layer 3...Magnetic layer 3a...GeFeCoCr film 3b...TbFeCoCr film 4...Second dielectric layer 5...Al reflective film

Claims (1)

[Claims] 1. A magneto-optical recording medium in which a first dielectric layer, a magnetic layer, a second dielectric layer, and a reflective film are laminated in this order on a substrate, wherein the magnetic layer is made of Gd, Fe, and Co. A first rare earth-transition metal alloy film containing Tb, Fe and C
a second rare earth-transition metal alloy film containing o, the total thickness of the magnetic layer is 200 to 300 Å, and the film thickness of the first rare earth-transition metal alloy film is equal to the total thickness of the magnetic layer. 2. A magneto-optical recording medium characterized in that the recording medium is 20% to 50% of the average temperature.