JPH0370363B2 - - Google Patents

Description

[Detailed description of the invention]

More specifically, the present invention relates to a cobalt chromium perpendicular magnetic recording medium. 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, adding chromium reduces saturation magnetization and
By strongly aligning the C-axis of the close-packed hexagonal crystal in the direction perpendicular to the substrate, it becomes possible to create a perpendicular magnetic anisotropic film. However, if ultra-high-density magnetic recording is realized, the demagnetizing field for one bit should be considerably smaller than the maximum demagnetizing field of 4πMs (Ms is the saturation magnetization) for thin films, and it is not necessarily the case that Ku > 2πMs ² (Ku is It is considered that it is not necessary to satisfy the condition (the crystal anisotropy constant of the magnetized film). On the other hand, in the case of a bulk Co-Cr perpendicularly magnetized film, the saturation magnetization of cobalt decreases linearly as the chromium content increases, but this shows that the saturation magnetization decreases slightly higher than that straight line. It is predicted that chromium is segregated at grain boundaries, and this was recently demonstrated by Auger electron spectroscopy of a cross section of the film. In other words, in order to lower the saturation magnetization and reduce the demagnetizing field, an appropriate amount of chromium is mixed into the crystal grains, and chromium is segregated at the grain boundaries.
The ideal perpendicular magnetic recording medium is to reduce the magnetization mechanism caused by domain wall movement by forming a nonmagnetic layer, magnetically separate crystal grains, and only rotate the magnetization of single domain grains. It will be done. 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: Cr content 22 (wt%) △θ ₅₀ 3.9 (deg) Hc (⊥) 1600 ( Oe) Hc (〃) 350 (Oe) Hk 5700 (Oe). This is an example of changing the input power,
A similar tendency is shown when the substrate is heated. In other words, due to the heat applied during film formation,
Both the coercive force Hc and the anisotropy 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, the write current and overwrite characteristics are improved, but because the original perpendicular anisotropy field of perpendicular magnetic recording is small, the magnetization reversal in high-density recording is sharp. Instead, the recording density characteristics deteriorate. In view of these points, the present invention solves these difficulties by further adding at least one of the metals of Groups A to A of the Periodic Table and Period 6 as a third element to the Co-Cr system. be. 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. In the present invention, in addition to Co-Cr, hafnium (hereinafter referred to as
Abbreviated as Hf. ) is clearly effective by containing 10 to 40 wt% (3.5 to 17.8 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 Hf added exceeds 40 wt%, the crystallinity of the film decreases significantly and the perpendicular anisotropy of the film drops sharply. Furthermore, if the amount of Hf added is less than 10 wt%, there is almost no effect of increasing the perpendicular anisotropy of the film. Conventional
In CoCr binary system, it was said that both magnetic properties and crystal orientation are good when Cr is in the range of 12 to 30 wt%.
By adding the metals of Groups A to A of the periodic table and period 6 of the present invention, the lower limit of the amount of Cr was widened, and better characteristics were exhibited than in the case of a binary system. FIG. 1 shows the effect of the present invention using Hf and W as examples. The numbers in the table represent the contents of Cr, Hf, and W in Co in weight percent. The shaded area is the area where the perpendicular magnetic anisotropy is improved by the present invention, and the other areas are areas where the effect of the present invention is not exhibited. Specific examples include thin film fabrication methods such as DC sputtering, RF sputtering, magnetron sputtering, opposed target sputtering, ion plating, electron beam evaporation, and plating, or substrate materials such as polyethylene terephthalate, polyimide, glass, and alumite-treated aluminum substrates. Regardless, there is an effect of adding the metals of Groups A to A of the periodic table and period 6 of the present invention. In general, perpendicular magnetic recording media have a single perpendicular magnetic recording layer and a high magnetic permeability layer is provided thereunder as a backing layer. Even if various changes are made to the Co-based or Fe-based amorphous high permeability thin film, it will still work. 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-Hf perpendicular magnetization film was formed. Target is Co-13wt%Cr, Co-16wt%
Three types of Co-Cr alloy targets were used: Cr and Co-20wt%Cr. For Co-Cr-Hf ternary perpendicular magnetization film, 5×
Thin films with various amounts of Hf were prepared by arranging Hf pellets with a size of 5 x 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 (water-cooled) 50μm polyimide Baking and baking of bell jar before sputtering , the polyimide substrate was degassed. 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 Hf pellets are placed on a Co-13wt%Cr target. Similarly, Co-16wt%
Tables 2 and 3 show the cases in which Cr and Co-20wt% Cr targets were used, respectively.

【table】

【table】

[Table] This data is the average of three experiments, and the Hf amount has an error of ±1%. This data reveals the following: By adding 40 wt% or less of Γ Hf, the perpendicular magnetic anisotropy increases by nearly 20%. As the amount of Γ Cr increases, the amount of Hf that takes the maximum value of the anisotropic magnetic field Hk shifts toward the lower side.
That is, the optimum amount of Hf addition changes depending on the value of x in Co _100- xCrx. When 40 wt% or more of Γ Hf is added, the crystal orientation deteriorates rapidly and the perpendicular magnetic anisotropy also decreases rapidly. Example 2 A Co--Cr--W ternary media was produced on a polyimide tape using an ion plating apparatus equipped with three electron beam evaporation sources and a coil for applying high frequency waves between the substrate and the electron beam evaporation sources. Each electron beam evaporation source has Co, Cr, and W.
By controlling the power of each electron beam, it is possible to change the composition of the deposited film. The film formation rate was about 5000 Å/sec. In the experiment, the power ratio of the Co and Cr evaporation sources was changed in three stages, and the weight ratio of Co and Cr in the produced film was 90:10,
The composition of the three elements was changed by varying the W power for the 85:15 and 80:20. In any case, when the amount of W exceeded 40% by weight, Hk decreased rapidly. The situation is shown in Figure 2. ○ mark indicates a ratio of Co to Cr of 90:10, △ mark indicates a ratio of Co to Cr
85:15, × indicates the ratio of Co to Cr is 80:20. Example 3 A video tape was produced and image processed using a facing target sputtering device. FIG. 3 shows a schematic diagram of a facing target type sputtering apparatus. A Co-Cr binary target 1, a dedicated DC power supply (hereinafter referred to as DC power supply) 2, and a Co-Cr-Hf ternary target 3 installed opposite it.
and a dedicated DC power supply 4 to generate a magnetic field of approximately 300 Gauss between the opposing targets, and an electromagnet 6 is provided outside the bell gear to prevent the substrate 5 from being exposed to plasma. The substrate 5 is
It is designed to be rolled up in a roll manner, and is movable up and down by a substrate holder 7 that can be heated and water cooled at the rear and a guide rod that moves with it. Sputtering conditions Target 1 Co ₈₄ Cr ₁₆ alloy target Target 2 (Co ₈₄ Cr ₁₆ ) ₈₆ Hf ₁₄ alloy target Initial vacuum 1.5×10 ^-7 torr Argon gas pressure 3×10 ^-3 torr Power 0 to 2.5KW Distance between targets 5cm Distance between target substrates: 4 cm Substrate (water-cooled) 1/2 inch width: 12.5 μm thick Mylar Film thickness: 0.4 μm This facing target type sputtering device has an independent power supply for each electrode, so the Co
- To change the amount of Hf in the Cr film, it was enough to change the power applied to each target, and the variation in film thickness distribution due to changing the power was controlled by the substrate holder and the top and bottom of the substrate. Figure 4 shows △θ ₅₀ and Hk when changing the amount of Hf.
shows the change in When Hf is below 40wt%, Hk is
It increases rapidly due to Hf addition. however,
It is thought that when 40 wt% or more of Hf was added, Δθ ₅₀ became abnormally large and the crystallinity and orientation deteriorated. Figure 4 is exactly the same as the trend in Figure 2,
There is no difference depending on the film forming apparatus and substrate. Example 4 Co-Cr was deposited on a glass substrate using an ion beam sputtering device that irradiates a target with an argon ion beam extracted from a Kauffman ion source.
- Created W3 original media. Co-10wt%Cr, Co-15wt%Cr, Co-20wt%
W pellets of 5 mm square and 1 mm thick were placed on three types of Cr targets and spattered by ion beam irradiation. The composition of Co--Cr--W deposited on the glass substrate changed depending on the number and arrangement of W pellets.
Regardless of which target is used, the crystal orientation and perpendicular anisotropy magnetic field improve by mixing a small amount of W, but when the amount of W exceeds 40 wt%, both the crystal orientation and the perpendicular anisotropy magnetic field improve. It got extremely worse. Example 5 Using the 8-inch magnetron sputtering device described above, a 5-inch collapsible medium for recording/reproduction 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 %), 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 Hf ₄ . The board is
50 μm thick polyethylene terephthalate was used. 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. The sputtering order was to form a 0.3 μm Co ₈₅ Zr ₁₅ film on separate substrates under the same conditions, then a 0.6 μm Co ₈₄ Cr ₁₆ film on one substrate, and a (Co ₈₄ Cr ₁₆ ) ₉₆ film on another substrate. A 0.6 μm Hf ₄ film was fabricated. Later, a film was formed on the opposite side under the same conditions to prevent warping on the media. Sputtering conditions Initial degree of vacuum <3×10 ^-7 torr Argon pressure 3×10 ^-3 torr Power 0.4A 240V Sputtering time ・CoZr...10min ・Co-Cr, Co-Cr-Hf...20min Target-substrate distance 50mm group Plate: 50 μm Mylar (PET manufactured by Dupont) FIG. 5 shows the configuration 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 is a 50 μm Mylar 8 film. Co ₈₅ Zr ₁₅ amorphous soft magnetic film 9 with a thickness of 0.3 μm on both sides
A (Co ₈₄ Cr ₁₆ ) ₉₆ Hf ₄ perpendicularly magnetized film 11 having a thickness of 0.6 μm is formed. Table 4 shows the characteristics of each film. However, Co ₈₄ Cr ₁₅ film and (Co ₈₄ Cr ₁₆ ) ₉₆ Hf ₄
The film has the characteristics of the underlying CoZr amorphous film that has been removed by etching.

[Table] Figure 6 shows the recording density characteristics when recording and reproducing media A and B, which are 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). From the figure, it can be seen that the second peak and third peak outputs of media B are considerably larger. At this time, CoCr
A Co-Cr-Hf ternary perpendicular magnetization film in which Hf is added to the film is superior to a CoCr binary film in practical use, and can sufficiently enable ultra-high density magnetic recording of 100 KFRPI or more. Example 6 Using a magnetron sputtering device with an 8-inch target, non-magnetic amorphous amorphous 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 W ₄ 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 provide the Co ₈₄ Cr ₁₆ and (Co ₈₄ Cr ₁₆ ) ₉₅ W above 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.
From the standard 3600 rpm to reduce the flying height.
I dropped it to 1000rpm. The flying height is about 0.2 μm. The magnetic head was a standard Mn-Zr-ferrite with a gap of 1 μm. Figure 8 shows the recording density characteristics when using disks C and D. The vertical axis is the relative output, and the horizontal axis is the recording density (unit:
KFRPI). Disc D with 4% W 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 ternary alloys such as Co--Cr--Hf, Co--Cr--W, etc., such as electron beam equipment, plating, and roll methods, may also be used. In addition, in Example 2, an example was given in which an improved device of the facing target method was used. There is nothing wrong with using the same ternary material for both targets and using the same DC or high frequency power source. In addition, in Examples 1 and 3, the substrate was water-cooled, but if the substrate was heated, the Co-Cr binary alloy film would have a high Hk = 6,800, but by adding Hf and W, the Hk = 7,800 to 8,500. It gets even higher. As explained above, the present invention provides a magnetic recording medium on which a perpendicularly magnetized film is formed, in which the perpendicularly magnetized film is a cobalt-chromium alloy containing 3.5 to 17.8 at% hafnium. Because it is a magnetic recording medium with the following characteristics, it is possible to increase the perpendicular magnetic anisotropy without significantly increasing the perpendicular coercive force of the perpendicularly magnetized film, making it possible to create an ultra-high-density recording medium with excellent recording density characteristics. It has the effect of being achievable.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the effects of the present invention. FIG. 2 explains Example 2, and is a diagram showing changes in the anisotropic magnetic field Hk with respect to the amount of W added. FIG. 3 and FIG. 4 are for explaining Example 3, and show the configuration of the apparatus and the change in film characteristics with respect to the amount of Hf, respectively. Figure 5,
FIG. 6 is for explaining Example 5, and is a diagram showing the configuration of the media and the recording density characteristics of each media. Figures 7 and 8 are Example 6
1 is a diagram showing a configuration diagram of a magnetic disk and recording density characteristics of each magnetic disk. 1...CoCr alloy target, 2...DC power supply, 3
...CoCrHf 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
Membrane (0.6μm), 11...CoCrHf membrane (0.6μm), 12
...Aluminum disk (1.9mm), 13...Alumite,
14...CoTa film (0.5 μm), 15...CoCr film or CoCrHf film (0.3 μm).

Claims (1)

[Claims] 1. A magnetic recording medium on which a perpendicularly magnetized film is formed, wherein the perpendicularly magnetized film is a cobalt-chromium alloy containing 3.5 to 17.8 at% hafnium.