JPH01130320A - Perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve magnetic characteristics such as perpendicular magnetic anisotropy and mechanical characteristics by using a perpendicularly magnetized film consisting of a Co-BN material without contg. Cr as a recording layer. CONSTITUTION:The perpendicularly magnetized film having the compsn. expressed by Co1-x(BN)x (where x denotes a weight ratio and 0.08<=x<=0.74). A sputtering method using a Co target and BN target is adopted as a method for forming the perpendicularly magnetized film of the Co-BN system. The compsn. (x) of the perpendicularly magnetized of the Co-BN system is controlled and the magnetic characteristics, etc., are controlled according to purposes by increasing and decreasing the area of the BN target. The perpendicular magnetic recording medium which has the excellent magnetic characteristics such as perpendicular magnetic anisotropy and the excellent practicable characteristics such as mechanical characteristics and lubricity is thereby obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is used in the so-called perpendicular magnetic recording method, which records and reproduces signals using residual magnetization in the direction perpendicular to the surface of the recording medium. The present invention relates to perpendicular magnetic recording media, and particularly relates to a new perpendicular magnetic recording medium that can replace Co--Cr-based perpendicular magnetic recording media.

[Summary of the invention]

The present invention provides perpendicular magnetism that has excellent magnetic properties such as perpendicular magnetic anisotropy and coercive force, as well as excellent practical properties such as mechanical properties and lubricity, by constructing the perpendicular magnetization film from a Co-0N-based material. This is an attempt to realize a recording medium.

[Conventional technology]

Conventionally, in order to perform recording and reproduction on a magnetic recording medium used as a storage medium of a computer, an audio tape recorder, a video tape recorder, etc.,
Generally, a magnetic layer deposited on a substrate is magnetized in a direction parallel to the surface of the substrate (in-plane magnetization), and recording and reproduction is performed using residual magnetization in that in-plane direction.

However, in the case of recording using in-plane direction magnetization, as the wavelength of the recording signal becomes shorter, that is, as the recording density increases, the demagnetizing field within the medium increases and the residual magnetic flux density attenuates.
This has the disadvantage that the reproduction output is reduced.

Therefore, a perpendicular magnetic recording method has been proposed in which recording and reproduction is performed by magnetization in the thickness direction of the magnetic layer of a magnetic recording medium. According to this perpendicular magnetic recording method, as the recording wavelength becomes shorter, the demagnetizing field is reduced. Since it is advantageous over recording using in-plane direction magnetization, especially in high-density recording, it is being actively researched.

By the way, as perpendicular magnetic recording media used in this type of recording system, those in which a perpendicularly magnetized film formed of a Co--Cr alloy material or the like on a non-magnetic support as a recording layer have been mainly studied. This is because this Co--Cr-based perpendicularly magnetized film has very excellent magnetic properties such as perpendicular magnetic anisotropy and coercive force.

However, Co--Cr based perpendicular magnetization films have many problems in mechanical properties, such as being hard and having very large internal stress, and have not been put into practical use.

[Problem that the invention seeks to solve]

As described above, although the Co-Cr-based perpendicular magnetization film has excellent magnetic properties, it has poor practical properties for use as a magnetic recording medium.
Therefore, the realization of a new perpendicular magnetization film to replace the Co--Cr-based perpendicular magnetization film is awaited.

Therefore, the present invention has been proposed in view of the above-mentioned conventional situation, and is a perpendicular magnetic material that has excellent not only magnetic properties such as perpendicular magnetic anisotropy but also practical properties such as mechanical properties and lubricity. The purpose is to provide recording media.

[Means for solving problems]

One of the reasons why the above-mentioned Co--Cr-based perpendicular magnetization film is hard is that it contains a large amount of Cr.

Therefore, the present inventor has conducted extensive research to develop a perpendicularly magnetized film that exhibits good perpendicular magnetic anisotropy without using Cr.
It has been found that a Co-BN-based material containing Go and BN (boron nitride) functions as a perpendicularly magnetized film within a predetermined composition range.

The present invention was completed based on this knowledge, and includes CO+-x(BN)x (where X represents a weight ratio and satisfies 0.08≦x≦0.74). The present invention is characterized in that a perpendicular magnetization film (hereinafter referred to as a Co-BN-based perpendicular magnetization film) having the following composition is formed.

In the perpendicular magnetic recording medium of the present invention, the above G.

-The ratio X of BN in the BN-based perpendicular magnetization film is 0.0
It is necessary that the range is 8≦x≦0.74, and if it is outside this range, perpendicular magnetic anisotropy will not be exhibited, especially when the value of X is 0.
．． When it exceeds 75, it becomes non-magnetic.

As a method for forming the above-mentioned Co-BN perpendicular magnetization film, C
A sputtering method using an o target and a BN target is employed. Here, the composition X of the Co-BN-based perpendicular magnetization film obtained can be controlled by increasing or decreasing the area of the BN target, and the magnetic properties etc. can be controlled depending on the purpose. In this case, in order to function as a perpendicularly magnetized film, the perpendicular anisotropy magnetic field Hk must be 20
It is preferable to control it so that it is 0 (Oe) or more.

Although reactive sputtering in a nitrogen atmosphere is also considered as a film forming method, in this case it is difficult to ensure predetermined mi characteristics, etc., and it cannot be said to be a preferable method.

The Co-BN-based perpendicular magnetization film formed by this method is considered to be an amorphous film because no peaks are observed when performing X-ray diffraction and it has a crystallization temperature. .

On the other hand, there are no restrictions on the material of the substrate, and any materials conventionally used as substrate materials for this type of media can be used. Examples include polyester, polyolefins, cellulose derivatives, and vinyl. Polymer supports made of polymer materials such as resins, polyimides, polyamides, polycarbonates, etc., metal substrates made of aluminum alloys, titanium alloys, etc., ceramic substrates made of alumina glass, etc., and glass substrates. etc.

[Effect]

In the perpendicular magnetic recording medium of the present invention, Co serves as the recording layer.
The -BN-based perpendicularly magnetized film exhibits good perpendicular magnetic anisotropy depending on its composition, and since it does not contain C, the film is relatively soft and has low internal stress.

In addition, as a component of the perpendicularly magnetized film, B, which has lubricating properties, is also used.
Since N is included, runnability, which is one of the important practical properties, is ensured.

〔Example〕

The present invention will be explained below based on specific experimental results.

Various experiments were conducted using the film formation conditions shown below as basic conditions.

Film formation method with bottom plate stripes j R-F magnetron sputtering target: Co (3 inches in diameter) + BN pellets (5 squares) Sputtering gas = Ar Sputter pressure crab 1.5 x 10-” to 3 x 10
-'TorrRF output 150W (some 55W~27
0W) Substrate cooling: Water cooling (partial heating 24-300℃)
) Distance between target substrates: approximately 5.7 cm Ultimate pressure: 5 x 10-'Torr or less Substrate film thickness: 1,000 to 2,000 First, C by changing the BN composition and sputtering pressure.

- A BN-based perpendicular magnetization film was produced. Figure 1 shows the magnetic properties of the film obtained by plotting the BN composition and sputtering pressure on the vertical and horizontal axes, respectively. , and N represents non-magnetic.

Furthermore, the shaded area in the figure is an area exhibiting vertical anisotropy.

From this Figure 1, when the proportion X of BN in the Go-BN-based perpendicularly magnetized film is within the range of 0.08≦x≦0.74, especially on the low sputtering pressure side, it becomes ferromagnetic and perpendicularly magnetic. It can be understood that it exhibits anisotropy.

Next, Figure 2 shows a typical hysteresis loop of a film exhibiting perpendicular magnetic anisotropy.The composition of this film is COts, 1
ss(BN)o, s4s (however, the numerical value is 4; !The composition is expressed as a ratio of 1 to 1, the same applies hereinafter), and the sputtering pressure during film formation is 1.5 x 10-'' Torr.

In FIG. 2, // represents a hysteresis loop in the in-plane direction (in-plane hysteresis loop), and soil represents a hysteresis loop in the vertical direction.

The saturation magnetization Ms obtained from these hysteresis loops is 4
70 emu/cc, coercive force Hc in the in-plane direction is 50 (
The perpendicular coercive force Hc was 350 (Oe), and the perpendicular anisotropy magnetic field Hk determined from the in-plane hysteresis loop was 1880 (Oe), which is a good value for a perpendicularly magnetized film. This was confirmed.

In the above hysteresis loop, especially from the in-plane hysteresis loop, it was suggested that the Co-BN-based perpendicularly magnetized film has a portion with perpendicular anisotropy and a portion without perpendicular anisotropy. In other words, in the hysteresis loop schematically shown in Figure 3, the slope before the magnetization saturates comes from a part with perpendicular anisotropy, and the magnetization jump near the coercive force comes from a part without perpendicular anisotropy. It is thought to have originated from

Therefore, the film thickness dependence of the saturation magnetic moment indicated by 0 in FIG. 5 and the in-plane magnetic moment indicated by Δ was investigated. The film compositions were COo, ass(BN)o, and sas, and the sputtering pressure during film formation was 3 x 10-'Tor.
It is r.

As a result, as shown in FIG. 4, it was found that the in-plane magnetic moment did not increase even if the film thickness increased, but the saturation magnetic moment gradually increased as the film thickness increased.

Furthermore, the coercive force Hc in the in-plane direction and the perpendicular anisotropy magnetic field Hk
The film thickness dependence was also investigated. According to this figure, the curve plotted with the 0 mark in Fig. 5 shows the film thickness dependence of the coercive force Hc, and the curve plotted with the Δ mark shows the film thickness dependence of the perpendicular anisotropy magnetic field Hk. , the coercive force shows almost no film thickness dependence, and only the perpendicular anisotropy field increases with increasing film thickness.

Therefore, from FIGS. 4 and 5, it can be seen that the magnetic moment and coercive force of the portion without perpendicular anisotropy have no dependence on the film thickness, and from this, the sputtering initial layer (
(approximately 300 people) concluded that they do not have vertical anisotropy.

Next, the influence of the sputtering pressure upon forming a Co-BN-based perpendicularly magnetized film on the magnetic properties of the resulting film was investigated. In this experiment, the film composition was C001is(BN).
. ,,4S.

FIG. 6 shows the dependence of the saturation magnetization Ms and the initial layer magnetic moment on the sputtering pressure, and FIG. 7 shows the dependence of the perpendicular anisotropy magnetic field Hk and the coercive force Hc on the sputtering pressure.

It can be seen from FIGS. 6 and 7 that the lower the sputtering pressure, the better the magnetic properties, especially the perpendicular anisotropy magnetic field Hk, and the thinner the initial layer without perpendicular anisotropy.

Furthermore, differences in magnetic properties depending on BN composition were investigated. Sputter pressure is 3 x 10-'Torr. , Fig. 8 shows the dependence of the perpendicular anisotropy magnetic field Hk and the initial layer thickness on the BN composition, and Fig. 9 shows the dependence of the saturation magnetization Ms and the coercive force Hc in the in-plane direction on the BN composition. .

As a result, first of all, from Fig. 8, when the BN composition is 51% by weight, the vertical anisotropy magnetic field Hk has a maximum value (1900 (Oe)
), and at the same time it was found that the initial layer thickness became extremely small. On the other hand, from Figure 9, BN! It was found that when the composition exceeds 75% by weight, magnetism disappears and the film becomes a non-magnetic film.

Next, in order to determine the optimal values for sputtering conditions, changes in magnetic properties due to RF specific output substrate bias voltage, substrate temperature, etc. during sputtering were investigated. Note that the film composition in these experiments was COo, 4ss(BN)o, s4s, and the sputtering pressure during film formation was 3 x 10-'' Torr.

First, regarding the RF specific output, as is clear from Figs. 10 and 11, the smaller the RF specific output, the larger the perpendicular anisotropy magnetic field Hk, and at the same time the initial layer magnetic moment (
In other words, the initial layer thickness) becomes smaller. Therefore, it is advantageous to have the RF specific output as small as possible.

As shown in FIG. 12, the substrate bias voltage V has almost no effect on the saturation magnetization Ms or the coercive force Ha, but the first
As shown in Fig. 3, it has a large effect on the perpendicular anisotropy magnetic field Hk. In other words, the substrate bias voltage ① is approximately 100V.
When the perpendicular anisotropy magnetic field Hk has a maximum value of 2900 (
At the same time, as shown in FIG. 13, the initial layer magnetic moment disappears when the substrate bias voltage V is set to 50 V or more.

Figure 14 shows the hysteresis loop of a Co-BN perpendicular magnetization film obtained when the substrate bias voltage V is about 100V.
The broken line is the hysteresis loop in the vertical direction, the saturation magnetization Ms is 400 el+u/cc, the vertical coercive force is 250 (Oe), and the perpendicular anisotropy magnetic field Hk is 2900 (Oe).
e).

The coercive force Hc of the obtained film is as small as 250 (Oe), but the ratio of the residual magnetization M in the perpendicular direction to the residual magnetization M in the in-plane direction (M, I/M, is 1.6). It was confirmed that the film was perpendicularly magnetized.

Regarding the substrate temperature, the measurement results shown in FIGS. 15 and 16 show that it does not have much influence on the saturation magnetization Ms and the coercive force Hc, but the perpendicular anisotropy magnetic field T
(K increases as the substrate temperature increases, and is almost saturated at a substrate temperature of 200°C. On the other hand, the initial layer magnetic moment increases up to a substrate temperature of 100°C, and becomes smaller as the temperature further increases.

Finally, the influence of the base film upon forming the Co-BN-based perpendicular magnetization film was investigated.

In this experimental example, Ti was selected as the base film material, and a film composition C001ss (BN) was formed on the TI base film. , 43. A Go-BN-based perpendicularly magnetized film was formed under the conditions of a sputtering pressure of 3 x 10-'Torr during film formation, and changes in magnetic properties depending on the thickness of the Ti underlayer were investigated.

Figure 17 shows the saturation magnetization Ms and the initial layer magnetic moment T.
f Base Wl! FIG. 18 is a characteristic diagram showing the film thickness dependence, and FIG. 18 is a characteristic diagram showing the dependence of the perpendicular anisotropy magnetic field Hk and the coercive force Hc on the Ti underlayer film thickness.

As is clear from these FIGS. 17 and 18, regarding the saturation magnetization Ms, initial layer magnetic moment, and coercive force Hc, T? There is almost no effect of the thickness of the base film, and T
When the thickness of the i-base film is 7000 Å or more, a slight increase in the perpendicular anisotropy magnetic field Hk is observed.

Although the present invention has been described above based on specific experimental results, it goes without saying that the present invention is not limited thereto.

〔Effect of the invention〕

As is clear from the above explanation, in the present invention, C
Since the recording layer is a perpendicularly magnetized film made of a Co-BN-based material that does not contain any It is.

Further, in the present invention, it is possible to provide a perpendicular magnetic recording medium that contains BN used as a lubricant in the perpendicular magnetization film, reduces warp and friction coefficient, and has excellent running performance and durability.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the distribution of film properties depending on the BN composition and sputtering pressure, and FIG. Figure 3 is a schematic diagram of the hysteresis loop of a Co-BN perpendicular magnetization film, Figure 4 is a characteristic diagram showing the film thickness dependence of the saturation magnetic moment and in-plane magnetic moment in the Co-BN perpendicular magnetization film, and Figure 5 is a characteristic diagram showing the dependence of coercive force Hc and perpendicular anisotropy magnetic field Hk on film thickness, FIG. 6 is a characteristic diagram showing dependence of saturation magnetization Ms and initial layer magnetic moment on sputtering pressure, and FIG. 7 is a characteristic diagram showing perpendicular anisotropy. Figure 8 is a characteristic diagram showing the dependence of the perpendicular anisotropic magnetic field Hk and the coercive force He on the sputtering pressure. A characteristic diagram showing the dependence of the coercive force Hc on the BN composition in the in-plane direction, FIG. 10 is a characteristic diagram showing the dependence of the saturation magnetization Ms and the initial layer magnetic moment on the RF output, and FIG. 11 is a characteristic diagram showing the dependence of the perpendicular anisotropy magnetic field Hk. FIG. 12 is a characteristic diagram showing the dependence of coercive force Hc on RF output in the in-plane direction. FIG. 12 is a characteristic diagram showing the dependence of saturation magnetization Ms and coercive force Hc on substrate bias voltage. FIG. Hk
FIG. 14 is a characteristic diagram showing the hysteresis loop of the Co-BN perpendicular magnetization film obtained when the substrate bias voltage is 100 V, and FIG. 15 is a characteristic diagram showing the dependence of the initial layer magnetic moment on the substrate bias voltage. A characteristic diagram showing the dependence of magnetization Ms and initial layer magnetic moment on substrate temperature, Fig. 16 shows the perpendicular anisotropy magnetic field Hk and coercive force H in the in-plane direction.
Fig. 17 is a characteristic diagram showing the dependence of saturation magnetization Ms and initial layer magnetic moment on Ti underlayer film thickness, and Fig. 18 is a characteristic diagram showing the dependence of saturation magnetization Ms and initial layer magnetic moment on the substrate temperature. FIG. 3 is a characteristic diagram showing the dependence of the coercive force Hc on the thickness of the Ti underlayer film.

Claims (1)

[Claims] A perpendicular magnetism characterized in that a perpendicular magnetization film having a composition of Co_1_−_x(BN)_x (where x represents a weight ratio and satisfies 0.08≦x≦0.74) is formed on a substrate. recoding media.