JPS5873746A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To efficiently produce optical reproduction output by forming an amorphous thin film of a Tb-Fe-Co or Dy-Fe-Co ternary alloy having an axis of easy magnetization in the direction perpendicular to the film surface and specifying the composition of the constitutent elements. CONSTITUTION:A photomagnetic recording medium is obtd. by forming an amorphous thin film of a Tb-Fe-Co of Dy-Fe-Co ternary alloy having an axis of easy magnetization in the direction perpendicular to the film surface and 120-200 deg.C Curie point. The thin film is made amorphous by manufacturing a thin film on a substrate kept at a temp. below room temp. by sputtering or other method. It is required to regulate the composition consisting of Tb or Dy, Co and Fe to Tbx(Fe1-yCoy)1-x or Dyx(Fe1-yCoy)1-x (where 0.15<=x<=0.35 and 0<y<=0.5).

Description

Detailed Description of the Invention The present invention relates to a magneto-optical recording medium used in a magneto-optical memory, a magnetic recording display element, etc. Specifically, the present invention relates to a magneto-optical recording medium that has an easy magnetization direction perpendicular to the film surface, and has a circular or The present invention relates to a magnetic thin film recording medium in which information can be recorded by creating reversed magnetic domains of arbitrary shapes and read out using magneto-optic effects such as the magnetic Kerr effect.

In a ferromagnetic thin film whose axis of easy magnetization is perpendicular to the film surface,
51r7! Alternatively, it is possible to create a small reversal magnetic domain having a magnetic pole in the opposite direction to the uniform magnetization polarity in the plane of the film, which is uniformly magnetized to the N pole. The presence or absence of this inverted magnetic domain is determined by rlJ and r
If made compatible with OJ, such a ferromagnetic thin film can be used as a high-density magnetic recording medium. Among such ferromagnetic thin films, thin films that have a large coercive force at room temperature and have a Curie point or magnetic compensation temperature relatively close to room temperature can be irradiated with a light beam using the Curie point or magnetic compensation temperature. , it is generally used as a beam addressable file because information can be recorded by creating reversed magnetic domains at arbitrary positions.

Conventionally known ferromagnetic thin films that have an axis of easy magnetization in the direction perpendicular to the film surface and can be used as beam addressable files include polycrystalline metal thin films typified by MnB1, Gd-Co, and Gd. -Fe, Tb -F
e.

There are amorphous metal thin films such as Dy-Fe and compound single crystal thin films typified by GIG, but they have advantages and disadvantages as described below. A polycrystalline metal thin film that performs writing using a single Curie point, such as MnB1, is excellent as a magnetic recording medium in that it has a large coercive force of several KOe at room temperature, but it has a high Curie A (MnBi (T = 360°C), it has the disadvantage that it requires a large amount of energy for writing. Furthermore, since it is a polycrystalline material, it is necessary to produce a thin film with a chemical and stoichiometric composition, and it also has the disadvantage that it is technically difficult to produce a thin film. In addition, since the amorphous metal thin film that performs writing using the magnetic compensation points of Gd"Co and Gd-Fe is amorphous, it can be fabricated on any substrate, and it is possible to fabricate it on any substrate without adding some impurities. Although it has the advantage that the magnetic compensation temperature can be arbitrarily controlled to some extent, the coercive force at room temperature is small (300~□1)000e), and the recorded information is unstable. 3. ,,”'1G,
In order to produce a thin film having a coercive force of this level, it is necessary to control the formation to within approximately 1 atom%, which is not easy in terms of thin film production.

Furthermore, compound single crystal thin films typified by GIG have a major drawback in that they are extremely expensive compared to other films.

In addition, 15 atom % to 30 atom was proposed as a new magnetic thin film recording medium that eliminates these drawbacks.
The amorphous alloy thin film of TbFe or DyFe containing 1% or Dy has the following advantages.

(2) It has an axis of easy magnetization in the direction perpendicular to the film surface and has a large coercive force of several KOe at room temperature, so high-density information recording is possible and the recorded information is extremely stable.

■It has a large coercive force, making it possible to write magnetic domains in a desired shape.

■It has a large coercive force over a wide composition range, and has excellent properties as a recording medium.The composition range is also wide, so there is no need to create thin films with a strictly limited composition, making it very easy to use. It can be manufactured and has a good yield.

■One cucumber is 120℃ in TbFe, ,DyFe
Since the temperature is as low as 60 degrees Celsius, it is extremely small when performing thermal writing using a single point of Curi. Writing can be performed using T, energy.

However, this amorphous alloy thin film such as TbFe or DyFe has the following drawbacks. That is, if the Curie point is low, it is true that writing can be performed with small energy, but the S/N ratio when reading with light becomes worse. Figure 1 shows the optical reproduction output (S) and signal-to-noise ratio (S/N) during optical reproduction of an amorphous alloy thin film as a function of the irradiated laser power (Io), which can be used as a recording medium. It can be seen that TbFe and DyFe, which have such characteristics, are worse than GdFe, which is not good as a recording medium in terms of optical reproduction. This is a very serious drawback when considering this recording medium as a magneto-optical memory.

The object of the present invention is to conduct a magnetic field in a direction perpendicular to the above film surface.
It is an object of the present invention to provide a magneto-optical recording medium that can efficiently extract optical reproduction output by eliminating the drawbacks of conventional magneto-optical recording media having an easy axis.

The present invention will be explained in detail below.

The magneto-optical recording medium of the present invention is an amorphous material of Tb-Fe-C and Dy-Fe-Co which has an axis of easy magnetization in the direction perpendicular to the film surface and has a single Curie point between 120°C and 200°C. It is an alloy thin film. In order to have sufficient magnetic anisotropy to orient the magnetization in the direction perpendicular to the film surface, it is necessary to make the thin film amorphous, but this condition cannot be achieved on a substrate kept at a temperature below room temperature. This is achieved by fabricating a thin film using a sputtering method, a vacuum evaporation method, or the like. In addition, in order to stabilize the magnetization and direct it in the direction perpendicular to the film surface, the thickness of the film should be 100A" or more, and the composition of Tb or Dy, Fe, and Co should be changed to Tbx (Fe I
y Coy ) 1-X and Dyx (F'el-yCo
y) 1-, as 0.15<x<0.35.

o, oo (It is necessary to set the range of y≦050.

o, so (at y, the dependence of the key point or the magnetic compensation temperature on the composition is large, making it impractical. A magneto-optical recording medium in this composition range must have an axis of easy magnetization perpendicular to the film surface. This enables extremely high-density recording.

Although the magneto-optical recording medium of the present invention has a relatively low Curie point of about 120 to 200°C, the optical reproduction output using the magnetic Kerr effect has a similar Curie point. It is characterized by being larger than I. An example is TbFeC.

In the case of < , Tb (FeC
It can be seen that the Kerr rotation angle θ of (o) is improved as Co is added to the binary TbFe. In Figure 2,
The horizontal axis shows the ratio (chi) of Co to the entire TbFeCo. On the other hand, the coercive force He and key point T, which are related to recording characteristics, are
Regarding c, as shown in Table 1, the coercive force is TbF, e
Although it is considerably larger than the binary system, and the Curie point Tc increases slightly, the excellent recording characteristics of TbFe remain unchanged.

Table 1 As explained above, from this book: Ming's magneto-optical recording medium:
・1 is a well-known amorphous alloy thin film of TbFe, DyF
The features of amorphous alloy thin films are that they have an axis of easy magnetization in the direction perpendicular to the film surface like e.g., have a large coercive force at room temperature, have a single cucumber point close to room temperature, and are easy to fabricate. However, the optical reproduction output is larger than any of the conventional ones. Therefore, if it is used as a storage medium for a magneto-optical memory such as a so-called beam-addressable file memory, which writes using a light beam and reads using the Kerr effect, it has an extremely high density and a large S/N ratio. A memory device can be realized. It goes without saying that the writing method is not limited to a light beam, and may be performed by any method that supplies the energy necessary to generate reversed magnetic domains, such as a nail-shaped magnetic head, a hot pen, or an electron beam.

[Brief explanation of drawings]

FIG. 1 is a diagram of optical reproduction characteristics of a conventional amorphous alloy thin film, and FIG. 2 is a characteristic 1 showing the relationship between Co (%) and Kerr rotation angle: 11 θ3 of the present invention/GdDyCo thin film. Patent applicant Kokusai Telegraph and Telegraph Co., Ltd. agent Otsuka 1 external personΦ

Claims (1)

[Claims] Non-crystalline Tb- with an axis of easy magnetization perpendicular to the film surface
It has a Fe-Co or Dy-FeLCo ternary alloy thin film, 'rbx(Fe 1-y Coy ) 1-z +
1))'z (Fe 1-y Coy ) 1-z, X is in the range of 0.15<x≦0.35,
A magneto-optical recording medium characterized in that y is in the range of 0<y<o, so.