JPH0370362B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to magnetic recording materials, and more particularly to cobalt chromium perpendicular magnetic recording media. Magnetic recording media are used in computer storage devices and are generally magnetized in the longitudinal direction of the recording medium. However, such a magnetization method has a limit in increasing the recording density, and a method has been proposed in which magnetization is performed in a direction perpendicular to the surface of the recording medium, which makes it possible to achieve a much higher density. Cobalt chromium (hereinafter abbreviated as Co-Cr) is used for a perpendicular magnetic recording medium that can be magnetized in a direction perpendicular to a magnetic thin film, and a thin film is formed on a substrate by sputtering. To create a perpendicular recording medium, it is necessary to provide perpendicular magnetic anisotropy that overcomes the demagnetizing field in the direction perpendicular to the film surface. Close-packed hexagonal cobalt has large magnetocrystalline anisotropy in the C-axis direction, but because of its large magnetization, the shape magnetic anisotropy energy is large, making it impossible to obtain a perpendicular magnetic anisotropic film. Therefore, by adding chromium, it is possible to reduce the saturation magnetization and to strongly orient the C axis of the hexagonal close-packed crystal in the direction perpendicular to the substrate, thereby making it possible to create a perpendicular magnetic anisotropic film. However, when ultra-high-density magnetic recording is realized, the demagnetizing field for one bit is the maximum demagnetizing field in a thin film, 4πMs (Ms is saturation magnetization).
Therefore, it is considered that it is not necessary to satisfy the condition Ku>2πMs ² (Ku is the crystal anisotropy constant of the magnetized film). On the other hand, in the case of a Co-Cr perpendicularly magnetized film, the saturation magnetization of cobalt decreases continuously as the chromium content increases in the case of bulk, but the saturation magnetization tends to decrease at a rate slightly higher than that of the chromium content. Therefore, it is predicted that chromium is polarized at the grain boundaries, and this was recently demonstrated by Auger electron spectroscopy analysis of a cross section of the film. In other words, lower the saturation magnetization,
In order to reduce the demagnetizing field, a moderate amount of chromium is mixed into the crystal grains, and chromium is segregated at the grain boundaries to form a nonmagnetic layer, thereby reducing the magnetization mechanism due to domain wall movement. An ideal perpendicular magnetic recording medium is considered to be one in which the crystal grains are magnetically separated so that only the magnetization rotation of single domain grains occurs. In conventional Co--Cr perpendicular magnetization recording media, when the perpendicular anisotropy of the film (particularly represented here by the perpendicular anisotropy magnetic field HK) is increased, the coercive force Hc (⊥) in the perpendicular direction also increases. Place a Cr pellet on a 4 inch Co target,
An example of forming RF magnetron spatter on 12.5 μm thick polyimide is described below. Example 1 Initial degree of vacuum 3×10 ^-8 torr Input power 1KV 70mA Time 1 hour Film properties are Cr content 21 (wt%) △θ ₅₀ 3.8 (deg.) Hc (⊥) 750 (Oe) Hc () 200 ( Oe) HK 4000 (Oe) Example 2 Initial degree of vacuum 3.5×10 ⁸ torr Input power 2KV 127mA Time 10min Film properties are Cv amount 22 (wt%) △θ ₅₀ 3.9 (deg) Hc (⊥) 1600 (Oe) Hc () 350 (Oe) HK 5700 (Oe). This is an example when the input power is changed, but the same tendency is shown when the substrate is heated.
In other words, as heat is applied during film formation, both the coercive force Hc and the anisotropic magnetic field HK increase. However, this is actually very inconvenient. For perpendicular recording media, it is naturally desirable to have a high HK as shown in Example 2, but if Hc (⊥) becomes too large, magnetic heads using ferrite, permalloy, sendust, amorphous soft magnetic materials, etc. will be unable to reach saturation. , the current flowing through the head must be very large. Even if saturation recording is possible, there are drawbacks such as difficulty in erasing and deterioration of overwrite characteristics. On the other hand, in a case like Example 1, although the write current and overwrite characteristics are improved, the original perpendicular anisotropy field of perpendicular magnetic recording is small, so the magnetization reversal in high-density recording is not sharp. Therefore, the recording density characteristics deteriorate. In view of these points, the present invention solves these difficulties by further adding titanium as a third element to the Co-Cr system. An object of the present invention is to magnetically separate crystal grains and provide an ultra-high density magnetic recording medium. Another object of the present invention is to dramatically increase the output and resolution in ultra-high density magnetic recording of 100 KFRPI or more. The present invention further adds titanium (hereinafter, Ti) to Co-Cr.
It is abbreviated as ) is clearly effective by containing 2 to 10 wt% (2.4 to 11.9 at%). Here, wt% indicates weight% and at% is atomic%
shows. Also, wt% and at% are 1:1 with each other.
In the detailed explanation of the present invention, the content of elements will be expressed in wt% because it can be easily converted and the experiments in the examples of this application were conducted in wt%. Unify. When the amount of Ti added exceeds 10wt%, the crystallinity of the film decreases significantly, and the vertical anisotropy of the film drops sharply. Further, if the amount of Ti added is less than 2 wt%, there is almost no effect of increasing the perpendicular anisotropy of the film. Conventional
In the CoCr binary system, it was said that both magnetic properties and crystal orientation are good when the Cr content is in the range of 12 to 30 wt%.
The addition of Ti in the present invention broadened the lower limit of the amount of Cr and showed better properties than the binary system. FIG. 1 shows the effects of the present invention. The numbers in the table are Cr in Co and
The Ti content was expressed in weight%. The shaded area is the region where the perpendicular magnetic anisotropy is improved by the present invention,
Other areas are areas in which the present invention does not show any effects. Specific examples include DC sputtering, RF sputtering, magnetron sputtering, opposed target sputtering, electron beam evaporation, plating, and other thin film fabrication methods, and regardless of the substrate material, such as polyethylene terephthalate, polyimide, glass, or alumite-treated aluminum substrates, this method can be used. There is an effect of adding Ti according to the invention.
In general, perpendicular magnetic recording media may have a single perpendicular magnetic recording layer or a high permeability layer provided thereunder as a backing layer. , Co-based, and Fe-based amorphous amorphous high permeability thin films can be modified in various ways. Hereinafter, the present invention will be explained based on Examples. Example 1 Co-Cr and Co were applied to a polyimide substrate using an RF power supply.
-A Cr-Ti perpendicular magnetization film was formed. Target is Co-13wt%Cr, Co-16wt%
CrCo-20wt%Cr and three types of Co-Cr alloy targets were used. For Co-Cr-Ti ternary perpendicular magnetization film, 5×5×
Thin films with various amounts of Ti were prepared by arranging Ti pellets with a size of 1 mm so that the distribution was uniform. The content of each component was determined by XMA. Sputtering conditions Initial degree of vacuum <3×10 ^-7 torr Argon gas pressure 3×10 ^-3 torr Power 400w (0.26A 2.2KV) Sputtering time 15min Distance between target substrates 50mm Substrate 50μm polyimide Baking of Bergier and polyimide before sputtering I vented the gas from the board. During sputtering, the substrate holder was cooled with water. The sputtering time was 15 minutes, and the film thickness was about 0.6 μm. The half width Δθ ₅₀ of the rocking curve and the magnetic properties of the fabricated film are shown below. Table 1 shows the case where Ti pellets were placed on a Co-13wt%Cr target. At the same time Co−16wt%
Tables 2 and 3 show the cases in which Cr and Co-20wt% Cr targets were used, respectively.

【table】

【table】

[Table] The second figure shows the relationship between the anisotropic magnetic field HK and the amount of Ti.
As shown in the figure. This data is the average of three experiments, and the Ti content has an error of ±1%.
This data reveals the following: By adding 10 wt% or less of ΓTi, the perpendicular magnetic anisotropy increases by nearly 20%. As the amount of ΓCr increases, the amount of Ti that takes the maximum value of the anisotropic magnetic field HK shifts toward the lower side. That is, the optimum amount of Ti to be added changes depending on the value of x in CoA ₁₀₀ -x Crx. When ΓTi is added in an amount of 10 wt% or more, the crystal orientation deteriorates rapidly, and the perpendicular magnetic anisotropy also decreases rapidly. Example 2 A video tape was produced using a facing target sputtering device and subjected to image processing. 4 is a schematic diagram of the facing target sputtering apparatus of FIG. 3; FIG. It consists of a Co-Cr binary target 1, a dedicated DC power supply (hereinafter referred to as DC power supply) 2, a Co-Cr-Ti ternary target 3 provided opposite to it, and a dedicated DC power supply 4. A magnetic field of about 300 Gauss is generated between the substrates 5 and 5.
An electromagnet 6 is provided outside the bell jar so that the bell gear is not exposed to plasma. The substrate 5 is designed to be rolled up in a roll manner, and is movable up and down by a substrate holder 7 at the rear that can be heated and cooled by water, and a guide rod interlocked with the substrate holder 7. Sputtering conditions Target 1 Co ₈₄ Cr ₁₆ alloy target Target 2 (Co ₈₄ Cr ₁₆ ) ₈₆ Ti ₁₄ alloy target Initial vacuum 1.5×10 ^-7 torr Argon gas pressure 3×10 ^-3 torr Power 0 to 2.5KW Between targets Distance: 50cm Distance between target substrates: 4cm Substrate: 1/2 inch width, 12.5μm thick Mylar Film thickness: 0.4μm This facing target type sputtering device has an independent power supply for each electrode, so the Co
- To change the amount of Ti in the Cr film, it was sufficient to change the power applied to each target, and the variation in film thickness distribution caused by changing the power was controlled by the substrate holder and the upper and lower positions of the substrate. Figure 3 shows △θ ₅₀ and HK when the Ti amount is changed.
shows the change in In the range of Ti below 10%, HK
However, it increases rapidly with the addition of Ti. However, when Ti was added in an amount of 10% or more, Δθ ₅₀ became abnormally large, and it seems that the crystallinity and orientation deteriorated. The tendency in FIG. 4 is exactly the same as that in FIG. 2, and there is no difference depending on the film forming apparatus and substrate. Example 3 Using the 8-inch magnetron sputtering device, a 5-inch collapsible medium for recording/reproducing evaluation was produced. This sputtering device is equipped with three 8-inch targets. Electrode 1 has Zr pellets placed on the Co target so that the film composition is Co ₈₅ Zr ₁₅ (expressed in weight percent), and Electrode 2 for,
Co-16wt%Cr target, Co-16wt for electrode 3
Ti pellets were placed on the %Cr target so that the film composition was (Co ₈₄ Cr ₁₆ ) ₉₆ Ti ₄ . The substrate used was polyethylene terephthalate with a thickness of 50 μm. The film is generally made of PET or mylar, which has poor heat resistance, so we used a DC power source to form the film. As for the order of spatuta,
After forming 0.3 μm Co ₈₅ Zr ₁₅ films on separate substrates under the same conditions, a 0.6 μm Co ₈₄ Cr ₁₆ film was formed on one substrate, and a 0.6 μm (Co ₈₄ Cr ₁₆ ) ₉₆ Ti ₄ film was formed on another substrate. did. Later, a film was formed on the opposite side under the same conditions to ensure that there was no warping on the metal. Sputtering conditions Initial degree of vacuum <3×10 ^-7 torr Argon pressure 3×10 ^-3 torr Power 0.4A240V Sputtering time ・CoZr…10min ・Co−Cr, Co−Cr−Ti…20min Target substrate distance 50mm Substrate 50μm Mylar (made by Dupont)
PET) FIG. 5 shows the structure of the media produced in this example. Media A has a 0.3 μm thick Co ₈₅ Zr ₁₅ amorphous soft magnetic film 9 and a 0.6 μm thick Co ₈₄ Cr ₁₆ perpendicular magnetization film 10 formed on both sides of a 50 μm Mylar 8. Media B has a 50 μm Mylar 8. 0.3 μm thick Co ₈₅ Zr ₁₅ amorphous soft magnetic film 9 and 0.6 μm thick (Co ₈₄ Cr ₁₆ ) ₉₆ Ti ₄₄ perpendicular magnetization film 11 on both sides of the
was formed. Table 4 shows the characteristics of each film. However, the properties of the Co ₈₄ Cr ₁₆ film and the (Co ₈₄ Cr ₁₆ ) ₉₆ Ti ₄ film are obtained by etching away the underlying CoZr amorphous film.

[Table] Figure 6 shows the recording density characteristics when recording and reproducing media A and B, which were constructed from films exhibiting the above magnetic properties, using a 1.3 μm thick permalloy main pole-auxiliary pole type head. FIG. 6 is plotted on a log-log graph. The vertical axis represents relative output, and the horizontal axis represents recording density in units of (KFRPI). As can be seen from the figure, the second peak and third peak outputs of media B are considerably larger. This shows that when Ti is added to the CoCr film,
In practical use, the CoCrTi ternary perpendicular magnetization film
It is superior to CoCr binary films and can fully enable ultra-high density magnetic recording of 100 KFRPI or more. Example 4 Using a magnetron sputtering device with an 8-inch target, non-magnetic amorphous amorphous material was sputtered onto a 5-inch anodized aluminum disk.
Co ₅₀ Ta ₅₀ (weight %) was formed to a thickness of 0.5 μm, Co ₈₄ Cr ₁₆ was formed to a thickness of 0.3 μm for disk C, and (Co ₈₄ Cr ₁₆ ) ₉₆ Ti ₁₄ was formed to a thickness of 0.3 μm for disk D. The configuration diagram is shown in FIG. Table 5 shows the magnetic properties of the above two types of disks.

[Table] The reason why 0.5 μm non-magnetic amorphous Co ₅₀ Ta ₅₀ was provided as the lower layer was to reduce the roughness of the alumite-treated disk surface, and to layer Co ₈₄ Cr ₁₆ and (Co ₈₄ Cr ₁₆ ) ₉₅ Ti on top of it. This is to increase the magnetic properties of ₅ . Recording and reproduction were performed using the above two types of disks with a 5-inch Winchester disk drive.
In order to reduce the floating height, from the standard 3600 rpm,
I dropped it to 1000rpm. The flying height is about 0.2 μm. The magnetic head was a standard Mn-Zn-ferrite with a 1 μm gap. FIG. 8 shows the recording density characteristics when disk C and disk D are used. The vertical axis is relative output, and the horizontal axis is recording density (unit:
KFRPI). Disc D with 4% Ti added
Compared to disk C, the second peak value obtained twice the output. Note that the present invention is not limited to the above embodiments. Other means than sputtering that can produce the CoCrTi ternary alloy, such as electron beam evaporation, plating, and roll methods, may also be used. In addition, in Example 2, an example was given in which an improved device with a facing target method was used.
Once the distribution with the best perpendicular magnetic anisotropy in the CoCrTi ternary alloy is determined, there is nothing wrong with using the same ternary material for both targets and using a common DC and high frequency power source. In addition, the data of Example 1 and Example 2 are those when the substrate is water-cooled, and the characteristics of the Co-Cr binary alloy film, for example, HK=
Under the production conditions where He=6800 is higher, the effect of increasing He=7800 to 8500 by adding Ti is as follows.
No change at all. As explained above, the present invention provides a perpendicular magnetic recording medium in which a perpendicular magnetization film is formed, wherein the perpendicular magnetization film is an alloy consisting of three elements, and the alloy is a cobalt-chromium binary alloy. Since it is characterized by containing 2.4 to 11.9 at% of titanium as the third component, it is possible to increase the perpendicular magnetic anisotropy without significantly increasing the coercive force in the perpendicular direction of the perpendicularly magnetized film. This has the effect of realizing an ultra-high density recording medium with excellent recording density characteristics.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the effects of the present invention. FIG. 2 is a diagram for explaining Example 1, showing the change in anisotropic magnetic field HK with respect to the amount of Ti added, and FIGS. 3 and 4 are diagrams for explaining Example 2. 5 and 6 are diagrams for explaining Example 3, respectively, and a diagram showing the configuration of the device and changes in film properties with respect to the amount of Ti, and a diagram showing the configuration of the media and records of each media. Density Characteristics FIGS. 7 and 8 are diagrams for explaining Example 4, showing the configuration of the magnetic disk and the recording density characteristics of each magnetic disk. 1...CoCr alloy target, 2...DC power supply, 3
...CoCrTi alloy target, 4...DC power supply, 5...
Substrate, 6... Electromagnet, 7... Substrate holder, 8... Mylar (50 μm), 9... CoZr film (0.3 μm), 10... CoCr
Film (0.6 μm), 11...CoCrTi film (0.6 μm), 12...
Aluminum disk (1.9mm), 13...Alumite, 1
4...CoTa film (0.5μm), 15...CoCr film or
CoCrTi film (0.3μm).

Claims (1)

[Claims] 1. A perpendicular magnetic recording medium in which a perpendicular magnetization film is formed, wherein the perpendicular magnetization film is an alloy consisting of three elements, and the alloy is a cobalt-chromium binary alloy with a third component. A perpendicular magnetic recording medium characterized by containing 2.4 to 11.9 at% of titanium.