JP2013235623A - Sputtering target material for perpendicular magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sputtering target material suitable for forming a soft magnetic film of a perpendicular magnetic recording medium, which can form the soft magnetic film having both a good amorphous property and a good anticorrosive property.SOLUTION: There is provided a sputtering target material for a perpendicular magnetic recording medium which is expressed by a composition formula in an atomic ratio of (Co-Fe)-Cr-B-Zr, 30≤X≤100, 15≤a≤20, 5≤b≤10, and 0.2≤c≤5.0, and is composed of remainder inevitable impurities.

Description

  The present invention relates to a sputtering target material used for forming a soft magnetic film of a perpendicular magnetic recording medium.

  In recent years, the progress of magnetic recording technology has been remarkable, and the recording density of magnetic recording media has been increased to increase the capacity of drives. However, in the in-plane magnetic recording type magnetic recording medium that has been widely used in the past, when attempting to achieve a higher recording density, the recording bits become finer and cannot be recorded by a normal recording head. Therefore, a perpendicular magnetic recording system has been put to practical use as a system for solving these problems and improving the recording density.

  Perpendicular magnetic recording is a method in which the magnetic film of a perpendicular magnetic recording medium is formed so that the axis of easy magnetization is oriented perpendicular to the medium surface. Even if the recording density is increased, the demagnetizing field in the bit is used. This is a method suitable for high recording density with a small decrease in recording and reproduction characteristics. In the perpendicular magnetic recording system, a recording medium having a magnetic recording film and a soft magnetic film with improved recording sensitivity has been developed.

The soft magnetic film of such a magnetic recording medium has a role of returning the recording magnetic field from the magnetic head, and the saturation magnetic flux density is in the range of 0.2 to 1.7 T in order to draw the recording magnetic field strongly. (For example, refer to Patent Document 1). Further, the soft magnetic film is required to have an amorphous structure in order to reduce noise (see, for example, Patent Document 2). Further, due to the necessity of applying a strong recording magnetic field, the magnetic head and the magnetic layer have been made closer to each other, and the protective layer has been made thinner. For this reason, it has become impossible to expect the provision of corrosion resistance by the protective layer, and high corrosion resistance is also required for soft magnetic films (see, for example, Patent Document 3).
As a material for forming a soft magnetic film of a conventional perpendicular magnetic recording medium, an Fe—Co—Cr—B alloy sputtering target material to which Cr is added in order to improve the corrosion resistance of a thin film has been proposed (for example, a patent). Reference 4).

JP 2004-335068 A JP 2004-303377 A JP 2008-276859 A JP 2008-045173 A

The soft magnetic film formed using the Fe—Co—Cr—B alloy sputtering target material added with Cr disclosed in Patent Document 4 described above is advantageous in terms of high corrosion resistance.
However, according to the study of the present inventor, it has been confirmed that this Fe—Co—Cr—B alloy soft magnetic film has a low amorphous property and has a problem in reducing the noise described above.
An object of the present invention is to solve the above problems and provide a sputtering target material suitable for forming a soft magnetic film of a perpendicular magnetic recording medium having high amorphousness and high corrosion resistance.

The present inventor found that the Co-Fe-based alloy sputtering target material can significantly improve the amorphous property while suppressing the deterioration of the soft magnetic properties by the combined addition of B, Zr and Cr. did.
That is, the present invention provides a composition formula in the atomic ratio _{(Co X -Fe 100-X)} 100-a-b-c -Cr a -B b -Zr c, 30 ≦ X ≦ 100,15 ≦ a ≦ 20,5 It is a sputtering target material for perpendicular magnetic recording media that is represented by ≦ b ≦ 10 and 0.2 ≦ c ≦ 5.0, and the balance is inevitable.

  According to the present invention, a sputtering target material for forming a soft magnetic film having high amorphousness and high corrosion resistance can be provided, which is an effective technique for manufacturing a perpendicular magnetic recording medium that requires a soft magnetic film.

It is an X-ray diffraction profile of the soft magnetic film formed using the sputtering target material of the example of the present invention and the comparative example.

  As described above, an important feature of the present invention is that an optimum additive element for forming a soft magnetic film having high amorphousness and high corrosion resistance as a Co-Fe alloy sputtering target material for perpendicular magnetic recording media. The combination is that B, Zr and Cr are selected, and the optimum addition range of each element for realizing the above effect is found. The reason will be described in detail below.

The sputtering target material of the present invention contains 5 (atomic%) B (boron). B shows an eutectic equilibrium diagram with the base elements Co and Fe, and is therefore an effective element for forming an amorphous state. Furthermore, B, which is a metalloid element, is an effective element that can achieve both high saturation magnetic flux density and promotion of amorphization because the decrease in saturation magnetic flux density with respect to the added amount can be suppressed lower than other transition metal elements.
When the amount of B added is less than 5 atomic%, amorphization cannot be promoted. On the other hand, when the addition amount of B exceeds 10 atomic%, the amorphous property can be improved even by adding B alone, but the number of particles during sputtering increases due to an increase in the boride phase in the structure of the sputtering target material. There is. For this reason, in this invention, B is added in 5-10 atomic%.

The sputtering target material of the present invention contains 0.2 to 5.0 atomic percent of Zr. As described above, it is possible to promote amorphization by containing 5 to 10 atomic% of B. However, there is a case where a stable amorphous state cannot be obtained only by adding 10 atomic% or less of B having an amorphous forming ability to Co or Fe. As a result of studying to solve this problem, the present inventor has found Zr as an element that can improve amorphousness even with a small amount of addition due to a synergistic effect with B without impairing the effect of B described above.
In addition to Ti, Y, Nb, Hf, Ta, Pr, Gd, etc. can be considered as elements having an amorphous forming ability for Co and Fe, but Y, Hf, Pr, and Gd are rare metals and expensive. Therefore, it is not realistic. Moreover, Ti, Nb, and Ta have a lower amorphous forming ability than Zr, and when adding these elements to improve the amorphous nature, it is necessary to add more than 5.0 atomic% and saturation There is a problem that the magnetic flux density decreases.
When the amount of Zr added is less than 0.2 atomic%, the effect of improving the amorphous property is small. On the other hand, when the amount of Zr added exceeds 5.0 atomic%, the saturation magnetic flux density decreases. For this reason, in this invention, Zr is added in 0.2-5.0 atomic%.

The sputtering target material of the present invention contains 15 to 20 atomic% of Cr. This is because by adding Cr, a dense passive film can be formed, and the effect of improving the corrosion resistance of the soft magnetic film can be obtained. Cr is an element that can adjust the saturation magnetic flux density applied to the soft magnetic film. When the amount of Cr added is less than 15 atomic%, the effect of improving corrosion resistance cannot be obtained.
As a result of various studies, the present inventor has found that both Cr and Zr have a saturation magnetic flux density that is about 0.06 T lower with respect to an increase of 1 atomic%, and even if Cr and Zr are replaced with each other, It was confirmed that the effect hardly changed. From the above, high corrosion resistance and excellent soft magnetic properties can be achieved at the same time by replacing a part of Cr with Zr within the above-described range in order to improve the amorphous property.
In the present invention, the addition amount of Cr is set to 20 atomic percent or less because the saturation magnetic flux density is excessively reduced when it exceeds 20 atomic percent in relation to the above-described Zr addition amount.

The Co—Fe alloy serving as the base of the sputtering target material of the present invention has a composition range in which the composition formula in atomic ratio is (Co _X —Fe _100-X ) and 30 ≦ X ≦ 100. This is because a high saturation magnetic flux density and high corrosion resistance can both be obtained by using a Co—Fe alloy having this composition range as a base. If the atomic ratio of Co is lower than 30%, the corrosion resistance decreases, so the atomic ratio of Co to Fe is set in the range of 30 to 100%. More preferably, it is 70 to 90% of range.

  As a method for producing the sputtering target material of the present invention, either a melt casting method or a powder sintering method can be applied. Among these, for the sputtering target material containing B of the present invention, a powder sintering method that can control the boride in the microstructure that becomes the starting point of abnormal discharge and particle generation during sputtering film formation to be fine and uniformly dispersed is applied. It is preferable to do.

  In the powder sintering method, by pressing and sintering an alloy powder having a final composition as a raw material powder, or by pressing and sintering a mixed powder obtained by mixing a plurality of alloy powders and pure metal powders to have a final composition. It is possible to stably produce a sputtering target material having a structure in which boride is finely and uniformly dispersed. Among them, it is preferable to press-sinter the alloy powder having the final composition that can obtain a stable and finely dispersed structure of boride as a raw material powder.

  Moreover, the raw material powder used for the above-mentioned powder sintering forms a powder by pulverizing an ingot obtained by casting a molten alloy whose components are adjusted to a desired composition, or by spraying the molten alloy with an inert gas. It can be produced by a gas atomization method. Among them, the gas atomization method is preferable, in which a small amount of impurities is mixed and a spherical powder having a high filling rate and suitable for sintering is obtained. In order to suppress the oxidation of the spherical powder, it is preferable to use argon gas or nitrogen gas, which is an inert gas, as the atomizing gas.

As a sintering method of the raw material powder, it is possible to use pressure sintering such as hot isostatic pressing, hot pressing, discharge plasma sintering, extrusion press sintering, and the like. Among them, the hot isostatic press is particularly preferable because the pressurization pressure is high and a dense sintered body can be obtained even if the maximum temperature is kept low to suppress the formation of the diffusion layer.
In addition, it is preferable to set the maximum temperature at the time of pressure sintering to the temperature of 800-1200 degreeC. When the sintering temperature is less than 800 ° C., the powder does not sufficiently sinter and voids are formed, and when the sintering temperature exceeds 1200 ° C., the powder may be dissolved.
The maximum pressure during pressure sintering is preferably set to 20 to 200 MPa. When the pressure is less than 20 MPa, sufficient sintering cannot be performed, and voids are easily formed in the target structure. When the pressure exceeds 200 MPa, there is a problem that an apparatus that can endure is limited.
Moreover, it is preferable to set the sintering time held at the maximum temperature and the maximum pressure during pressure sintering to 1 to 10 hours. When the sintering time is less than 1 hour, the sintering cannot be sufficiently progressed. When the sintering time exceeds 10 hours, the production efficiency is remarkably deteriorated.

First, Fe ₇₀ -B ₃₀ (atomic%), Fe _84.6 -Zr _15.4 (atomic%), Co _97.6 -B _2.4 (atomic%), Co _{85 having a} purity of 99.9% or more, respectively. _.3- Zr _14.7 (atomic%) Each gas atomized powder having an alloy composition and Cr powder having a purity of 99.9% or more were prepared, and (Fe ₂₅ -Co ₇₅ ) ₇₃ -Cr ₁₇ -B ₈ -Zr ₂ was prepared. A mixed powder was prepared by weighing and mixing so as to be (atomic%).
After filling the above mixed powder into a pressure vessel made of mild steel and deaeration-sealing, a sintered body is produced by hot isostatic pressing under the conditions of a temperature of 950 ° C., a pressure of 150 MPa, and a holding time of 1 hour. A sputtering target material according to the present invention having a diameter of 190 mm and a thickness of 4 mm was obtained by processing.

Next, as comparative examples, each gas atomized powder having an alloy composition of Fe ₈₈ -B ₁₂ (atomic%), Co, and Co _97.6 -B _2.4 (atomic%) having a purity of 99.9% or more, and purity 99.9% or more of Cr powder was prepared, and weighed and mixed so as to be (Fe ₂₅ -Co ₇₅ ) ₇₅ -Cr ₁₉ -B ₆ to prepare a mixed powder. After filling the obtained mixed powder into a pressure vessel made of mild steel and degassing and sealing, a sintered body is produced by hot isostatic pressing under conditions of a temperature of 950 ° C., a pressure of 150 MPa, and a holding time of 1 hour, A sputtering target material serving as a comparative example having a diameter of 190 mm and a thickness of 4 mm was obtained by machining.

(Amorphous evaluation)
Each sputtering target material produced above is placed in the chamber of a DC magnetron sputtering apparatus (C3010 manufactured by Canon Anelva Co., Ltd.), and exhausted until the degree of vacuum in the chamber reaches 2.0 × 10 ⁻⁵ Pa or less. It was. Then, a soft magnetic film having a film thickness of 1000 nm was formed by sputtering on a glass substrate having a size of 70 × 25 mm under an Ar gas pressure of 0.6 Pa and an input power of 1 kW. Incidentally, the thickness of the soft magnetic film of the magnetic recording medium is generally 20 to 100 nm, but in this embodiment, the thick film was set to 1000 nm in order to evaluate the amorphous property.

About the sample of each soft-magnetic film | membrane obtained above, X-ray-diffraction measurement was performed using Rigaku Co., Ltd. X-ray-diffraction apparatus RINT2500V, using Co as a radiation source. The obtained X-ray diffraction profile is shown in FIG.
From FIG. 1, the soft magnetic film formed by using the sputtering target material in which a specific amount of B and Zr of the present invention is added in a composite amount has a high amorphous property because a diffraction peak due to the crystal structure is not observed. It was confirmed that
On the other hand, in the soft magnetic film formed using the sputtering target material of the comparative example to which B alone was added, diffraction peaks caused by the crystal structures of BCC (200) and (211) are slightly observed. Compared to the examples, it was confirmed that the amorphousness was low.
Further, according to the study of the present inventor, even when 9% by atom of B was added alone, a diffraction peak due to the crystal structure was confirmed as in the comparative example, and it was confirmed that the amorphous property was low.

(Evaluation of corrosion resistance)
Each sputtering target material produced above is placed in the chamber of a DC magnetron sputtering apparatus (C3010 manufactured by Canon Anelva Co., Ltd.), and exhausted until the degree of vacuum in the chamber reaches 2.0 × 10 ⁻⁵ Pa or less. It was. Then, a 200 nm thick soft magnetic film was formed by sputtering on a glass substrate having a size of 50 × 25 mm under an Ar gas pressure of 0.6 Pa and an input power of 1 kW.
The soft magnetic film sample obtained above was immersed in a nitric acid solution diluted to 10% with pure water at room temperature for 3 hours, and then the amount of Co eluted in the 10% nitric acid solution was subjected to inductively coupled plasma emission spectrometry. Was analyzed. The analyzed Co elution amount is shown in Table 1.

(Evaluation of saturation magnetic flux density)
Each sputtering target material produced above is placed in the chamber of a DC magnetron sputtering apparatus (C3010 manufactured by Canon Anelva Co., Ltd.), and exhausted until the degree of vacuum in the chamber reaches 2.0 × 10 ⁻⁵ Pa or less. It was. Then, a 40 nm thick soft magnetic film was formed by sputtering on a glass substrate having a size of φ10 mm under an Ar gas pressure of 0.6 Pa and an input power of 1 kW.

  For the soft magnetic film sample obtained above, a maximum magnetic field of 10 kA / m was applied in the in-plane easy magnetization axis direction using a vibrating sample magnetometer (model number: VSM-3) manufactured by Toei Industry Co., Ltd. The BH curve was measured to determine the saturation magnetic flux density. Table 1 shows the obtained saturation magnetic flux density.

From Table 1, the amount of Co eluted in the 10% nitric acid solution of the soft magnetic film formed using the sputtering target material of the present invention was similar to that of the soft magnetic film of the comparative example even when the amount of Cr added was smaller than that of the comparative example. Is less than 0.0001 mg / L, confirming that it has high corrosion resistance.
In addition, the saturation magnetic flux density of the soft magnetic film formed using the sputtering target material of the present invention is lower than that in the comparative example, which is because more B was added than in the comparative example. As a result of the inventor's investigation, it has been confirmed that when the B addition amount is increased by 1 atomic%, the saturation magnetic flux density is reduced by about 0.05 T, and when B is increased by 2 atomic% in the comparative example, It is estimated that the saturation magnetic flux density is almost equivalent to that of the invention example.
From the above, it can be confirmed that the soft magnetic film formed using the sputtering target material of the present invention has high amorphousness and high corrosion resistance, and the saturation magnetic flux density is in a range that can function as a soft magnetic film of a magnetic recording medium. It was.

Claims (1)

Composition formula in atomic ratio _{(Co X -Fe 100-X)} 100-a-b-c -Cr a -B b -Zr c, 30 ≦ X ≦ 100,15 ≦ a ≦ 20,5 ≦ b ≦ 10, A sputtering target material for a perpendicular magnetic recording medium, which is represented by 0.2 ≦ c ≦ 5.0, and is composed of the remaining inevitable impurities.