JPH0465523B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a magneto-optical recording medium used in a magneto-optical memory, a magnetic recording display element, etc., and specifically has an axis of easy magnetization in a direction perpendicular to the film surface, The present invention relates to a magnetic thin film recording medium in which information can be recorded by creating inverted magnetic domains in a circular or arbitrary shape, and in which information can be read out using magneto-optic effects such as the magnetic Kerr effect. (Prior art) In a ferromagnetic thin film in which the axis of easy magnetization is perpendicular to the film surface, there is a small reversal in which the film surface is uniformly magnetized to the S or N pole and has a magnetic pole in the opposite direction to the uniform magnetization polarity. Can create magnetic domains. If the presence or absence of this inverted magnetic domain corresponds to "1" or "0", such a ferromagnetic thin film can be used as a high-density magneto-optical recording medium. Among these ferromagnetic thin films, thin films that have a large coercive force at room temperature and whose Curie point or magnetic compensation temperature is relatively close to room temperature are
It is generally used as a beam-addressable film because information can be recorded by creating an inverted magnetic domain at an arbitrary position using a light beam using the Curie point or magnetically compensated temperature. 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 MnBi, Gd-Co, Gd−Fe,
There are amorphous metal thin films such as Tb-Fe and Dy-Fe, and compound single crystal thin films typified by GIG, each of which has advantages and disadvantages as described below.
Polycrystalline metal thin films, such as MnBi, which perform writing using the Curie point, are excellent as magneto-optical recording media in that they have a large coercive force of several kOe at room temperature, but the Curie point is high ( MnBi has the disadvantage that it requires a large amount of energy for writing because Tc = 360°C). Furthermore, since it is a polycrystalline material, it is necessary to produce a thin film with a stoichiometric composition, which 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, without adding some impurities. Although it has the advantage that the magnetic compensation temperature can be arbitrarily controlled to some extent, it has the disadvantage that the coercive force at room temperature is small (300 to 500 Oe) and the recorded information is unstable. Moreover, in order to produce a thin film with this level of coercive force, the composition must be adjusted to approximately
It is necessary to control within latom%, 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, 15atom% to 30atom% has been proposed as a new magnetic thin film recording medium that eliminates these drawbacks.
TbFe or DyFe amorphous alloy thin films containing Tb or Dy have the following advantages. It has an axis of easy magnetization perpendicular to the film surface and has a large coercive force of several kOe at room temperature.
High-density information recording is possible, and the recorded information is extremely stable. It has a large coercive force and can 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.Because the composition range is also wide, there is no need to create a thin film with a strictly limited composition, and it can be produced very easily. , yield is also good. The Curie point is 120℃ for TbFe and 120℃ for DyFe.
Since the temperature is as low as 60°C, when performing thermal writing using the Curie point, writing can be performed with extremely small energy. (Problems to be Solved by the Invention) However, this amorphous alloy thin film of TbFe, DyFe, etc. 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.
is shown as a function of the irradiated laser power (Io), and it has good characteristics as a recording medium.
It can be seen that TbFe and DyFe 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 purpose of the present invention is to increase the coercive force of the conventional Dy-Fe binary amorphous metal thin film having the axis of easy magnetization in the direction perpendicular to the film surface, and to efficiently reproduce optical output. The object of the present invention is to provide a removable magneto-optical recording medium. (Means for Solving the Problems) The magneto-optical recording medium of the present invention has an amorphous Dy-Fe-Co ternary alloy thin film having an axis of easy magnetization in a direction perpendicular to the film surface _. (Fe _1-y Co _y ) When _1-x ,
x is in the range of 0.15≦x≦0.35, y is in the range of 0.00<y≦
0.50, and the Curie point is within the range of 120℃ or higher for thermal writing using the Curie point, which increases the coercive force compared to the Dy-Fe binary amorphous alloy thin film and efficiently writes. The device is characterized in that it is configured so that optical reproduction output can be taken out. The present invention will be explained in detail below. The magneto-optical recording medium of the present invention is an amorphous alloy thin film of Dy-Fe-Co having an axis of easy magnetization in the direction perpendicular to the film surface and a Curie point between 120°C and 200°C. In order to have sufficient magnetic anisotropy to orient the magnetization in the direction perpendicular to the film surface, it is necessary to make it amorphous, but this condition is achieved by forming a thin film by sputtering or vacuum evaporation. This is achieved by In addition, in order to stably direct the magnetization in the direction perpendicular to the film surface, the film thickness should be 100 Å or more, and as described above, Dy, Fe, Co
Assuming the composition of Dy _x (Fe _1-y Co _y ) _1-x , x is 0.15≦x
The range is ≦0.35, and it is necessary that y be in the range of 0.00<y≦0.50. In addition, when 0.50<y,
The Curie point or magnetic compensation temperature largely depends on the composition, making it impractical. In addition, magneto-optical recording media in which the x range is outside this composition range have difficulty aligning the axis of easy magnetization in the direction perpendicular to the film surface, and the square hysteresis characteristic deteriorates, making it difficult for practical recording and reproduction. The characteristics will not be obtained. Although the magneto-optical recording medium of the present invention has a relatively low Curie point of about 120 to 200°C, it has been found that the optical reproduction output using the magnetic Kerr effect is greater than that of DyFe, which has a similar Curie point. It is a feature. (Example) FIG. 2 is a characteristic diagram of the amount of Co added and the Kerr rotation angle Θ _k of the Dy-Fe-Co ternary alloy thin film according to the present invention. The figure shows the characteristics when the film thickness is 1000 Å and part of the Fe in the DyFe binary system is replaced with Co.
By adding about 10 atom%, the Kerr rotation angle is doubled to 0.2 degrees, so it can be seen that the readout characteristics can be significantly improved compared to the DyFe binary system. Note that the composition of Dy in FIG. 2 was determined so that room temperature was the compensation temperature. As shown in the figure, when the amount of Co added is increased, the increasing trend slows down from about 40 atom%, but as the amount of Co increases, the Kerr rotation angle also increases. Further, when the composition ratio of Dy is increased, the Kerr rotation angle decreases as the ratio of Dy increases. On the other hand, FIG. 3 is a characteristic diagram of the amount of Co added and the coercive force Hc in the vicinity of each compensation composition (composition where room temperature is the compensation temperature) of the Dy-Fe-Co ternary alloy thin film according to the present invention. In the diagram, y is 0atom% in the characteristic diagram.
In the case of DyFe binary system (compensation composition x _a : Dy approximately 23.7%),
The characteristic diagram shows the case where y is added at 10 atom% (compensation composition x _b : Dy approximately 24.3%), the characteristic diagram shows the case where y is added at 20 atom% (compensation composition x _c : Dy approximately 25.1%), and the characteristic diagram shows the case where y is added at 34 atom % (compensation composition x _d :
Dy approximately 25.9%), and the characteristic diagram shows the case where 50 atom% of y is added (compensation composition X _e : Dy approximately 26.8%). Regarding the effect of increasing coercive force, as mentioned in the section on conventional technology, it is possible to record high-density information, the recorded information is extremely stable, and it is possible to write magnetic domains in the desired shape. It is possible to improve recording characteristics such as Therefore, in the present invention, by increasing the amount of Co added, it is possible to increase both the Kerr rotation angle, which is related to readout characteristics, and the coercive force, which is related to recording characteristics, so that both recording and optical reproduction characteristics are improved. can be improved. The fact that this optical reproduction characteristic is also improved will be explained from the following Curie temperature Tc. FIG. 4 is a characteristic diagram of the amount of Co added and the Curie temperature Tc of the Dy-Fe-Co ternary alloy thin film according to the present invention. As shown in the figure, the Curie temperature Tc increases significantly in proportion to the amount of Co added. Therefore, DyFe
The binary system has an extremely low Curie point of 60°C, and while it can be written with small energy, it causes a deterioration of S/N during optical reproduction, but by adding Co, the Curie point can be raised to over 120°C. be able to. On the other hand, if the Curie point becomes higher than 360°C, the output of the light source such as a semiconductor laser used for writing becomes insufficient, making it impossible to write the Curie point, and magnetically compensated points such as Gd-Fe system Although writing is necessary, magnetically compensated point writing suffers from the drawbacks mentioned in the prior art. Table 1 shows the Dy-Fe binary system and the Dy-Fe-Co of the present invention.
This is a table for comparison with a ternary system, and shows the Curie temperature Tc, coercive force Hc, and Kerr rotation angle Θ _k in the vicinity of each compensation composition when the Co composition ratio is changed. Reproduction C (carrier)/N
The measurement conditions for (noise) are a bit length of 3 μm and a measurement bandwidth of 30 kHz. As is clear from Table 1, when the amount of Co added is small, the Curie temperature and coercive force are small, so sufficient regeneration C/N cannot be obtained, but when the amount of Co added is about 10% or more, C/N is not obtained. N is significantly improved. Generally, when the amount of Co added is constant, when the composition ratio of Dy is increased, the Kerr rotation angle, coercive force, and Curie temperature each decrease.

【table】

[Table] As is clear from Table 1, Dy from the compensation composition
When the amount of deviation in composition is approximately equal, in the Dy-Fe-Co ternary system in which a small amount of Co is added to the y-Fe binary system,
The Curie temperature Tc, coercive force Hc, Kerr rotation angle _Θk , and reproduction C/N are improved, but the effects become noticeable when the Curie temperature is 120°C or higher. In particular, the Curie temperature and Kerr rotation angle vary depending on the composition of Dy, and generally, as the composition ratio of Dy decreases, the Curie temperature and Kerr rotation angle tend to increase. (Effects of the Invention) As described above, the magneto-optical recording medium of the present invention has an axis of easy magnetization in the direction perpendicular to the film surface, like the well-known amorphous synthetic thin film DyFe, and has a large coercive force at room temperature. It has the advantage of an amorphous alloy thin film that it is easy to produce, and moreover, optical reproduction output can be extracted efficiently. Therefore, if it is used as a storage medium for so-called magneto-optical memory, in which writing is performed using a light beam and reading is performed using the Kerr effect, an excellent memory device with extremely high density and high S/N can be realized. can. 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 needle-shaped magnetic head, a thermal pen, or an electron beam.

[Brief explanation of the drawing]

Figure 1 shows the optical reproduction characteristics of a conventional amorphous alloy thin film.
Figure 2 is a characteristic diagram of Co addition amount and Kerr rotation angle of the DyFeCo thin film according to the present invention, and Figure 3 is a characteristic diagram according to the present invention.
A characteristic diagram of Co addition amount and coercive force of a DyFeCo thin film. FIG. 4 is a characteristic diagram of Co addition amount and Curie temperature of a DyFeCo thin film according to the present invention.

Claims (1)

[Claims] 1. An amorphous Dy-Fe-Co ternary alloy thin film having an axis of easy magnetization perpendicular to the film surface, Dy _x (Fe _1-y Co _y ) _1-x and When x is 0.15≦x≦
In the range of 0.35, y is in the range of 0.00<y≦0.50,
And the Curie point is 120℃ or higher and within the range where thermal writing using the Curie point is performed.
- A magneto-optical recording medium characterized in that it has a larger coercive force than a Fe binary amorphous alloy thin film and is configured to efficiently extract optical reproduction output.