Title:
Co-base target and method of producing the same
Kind Code:
A1


Abstract:
The invention relates to a Co-base target made of a sintered powder, having a restrained amount of oxygen, and a producing method thereof. The target contains from more than 10 to not more than 25 at % of B and not more than 100 ppm of oxygen. It may contain 30≧Pt≧5 at%, 30≧Cr≧10 at%, 10≧Ta>0 at% and/or 30≧Ni>0 at%. It may contain also from more than 0 (zero) to not more than 15 at% in total of one or more elements selected from the group consisting of Ti, Zr, Hf, V, Nb, Mo, W, Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and rare earth elements. The target is produced by melting a Co-base alloy together with an additive B in an amount of from more than 10 to not more than 25 at% whereby deoxidizing, rapidly cooling the molten metal to produce an alloy powder and sintering the alloy powder. It can be optionally produced by mixing the above alloy powder with another metal powder, more particularly consisting of one or more elements selected from the group consisting of Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and Pt, and sintering the powder mixture.



Inventors:
Ueno, Tomonori (Purchase, NY, US)
Murata, Hideo (Saihaku-gun, JP)
Taniguchi, Shigeru (Yasugi-shi, JP)
Ueno, Hide (Yasugi-shi, JP)
Application Number:
09/995567
Publication Date:
08/08/2002
Filing Date:
11/29/2001
Assignee:
HITACHI METALS, LTD.
Primary Class:
Other Classes:
75/244
International Classes:
C22C19/07; C23C14/34; (IPC1-7): C22C19/07
View Patent Images:



Primary Examiner:
WILKINS III, HARRY D
Attorney, Agent or Firm:
SUGHRUE, MION, ZINN, MACPEAK & SEAS (Washington, DC, US)
Claims:

What is claimed is:



1. A Co-base target produced by powder sintering, which comprises from more than 10 atomic % to 25 atomic % of B (boron) and not more than 100 ppm of oxygen as an impurity.

2. A Co-base target according to claim 1, which further comprises from more than zero to 10 atomic % Ta.

3. A Co-base target according to claim 1, which further comprises from more than zero to 30 atomic % Ni.

4. A Co-base target according to claim 1, which further comprises from more than zero to 10 atomic % Ta and from more than zero to 30 atomic % Ni.

5. A Co-base target according to claim 1, which further comprises from more than zero to 15 atomic % in a total amount of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Mo, W, Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and REM.

6. A Co-base target according to claim 5, which further comprises from more than zero to 10 atomic % Ta.

7. A Co-base target according to claim 5, which further comprises from more than zero to 30 atomic % Ni.

8. A Co-base target according to claim 5, which further comprises from more than zero to 10 atomic % Ta and from more than zero to 30 atomic % Ni.

9. A Co-base target produced by powder sintering, which consists essentially of from more than 10 atomic % to 25 atomic % of B (boron), 5 to 30 atomic % Pt, 10 to 30 atomic % Cr, not more than 100 ppm of oxygen as an impurity and the balance mainly of Co.

10. A Co-base target produced by powder sintering, which consists essentially of from more than 10 atomic % to 25 atomic % of B (boron), 5 to 30 atomic % Pt, 10 to 30 atomic % Cr, from more than zero to 10 atomic % Ta, not more than 100 ppm of oxygen as an impurity and the balance mainly of Co.

11. A Co-base target produced by powder sintering, which consists essentially of from more than 10 atomic % to 25 atomic % of B (boron), 5 to 30 atomic % Pt, 10 to 30 atomic % Cr, from more than zero to 30 atomic % Ni, not more than 100 ppm of oxygen as an impurity and the balance mainly of Co.

12. A Co-base target produced by powder sintering, which consists essentially of from more than 10 atomic % to 25 atomic % of B (boron), 5 to 30 atomic % Pt, 10 to 30 atomic % Cr, from more than zero to 10 atomic % Ta, from more than zero to 30 atomic % Ni, not more than 100 ppm of oxygen as an impurity and the balance mainly of Co.

13. A Co-base target produced by powder sintering, which consists essentially of from more than 10 atomic % to 25 atomic % of B (boron), 5 to 30 atomic % Pt, 10 to 30 atomic % Cr, from more than zero to 15 atomic % in a total amount of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Mo, W, Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and REM, not more than 100 ppm of oxygen as an impurity and the balance mainly of Co.

14. A Co-base target produced by powder sintering, which consists essentially of from more than 10 atomic % to 25 atomic % of B (boron), 5 to 30 atomic % Pt, 10 to 30 atomic % Cr, from more than zero to 10 atomic % Ta, from more than zero to 15 atomic % in a total amount of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Mo, W, Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and REM, not more than 100 ppm of oxygen as an impurity and the balance mainly of Co.

15. A Co-base target produced by powder sintering, which consists essentially of from more than 10 atomic % to 25 atomic % of B (boron), 5 to 30 atomic % Pt, 10 to 30 atomic % Cr, from more than zero to 30 atomic % Ni, from more than zero to 15 atomic % in a total amount of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Mo, W, Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and REM, not more than 100 ppm of oxygen as an impurity and the balance mainly of Co.

16. A Co-base target produced by powder sintering, which consists essentially of from more than 10 atomic % to 25 atomic % of B (boron), 5 to 30 atomic % Pt, 10 to 30 atomic % Cr, from more than zero to 10 atomic % Ta, from more than zero to 30 atomic % Ni, from more than zero to 15 atomic % in a total amount of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Mo, W, Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and REM, not more than 100 ppm of oxygen as an impurity and the balance mainly of Co.

17. A method of producing a Co-base target, which comprises: melting a Co-base alloy and an additive B (boron), whereby deoxidizing the Co-base alloy, subjecting the resultant Co-base alloy to a rapid cooling treatment to obtain a powder of the Co-base alloy, and sintering the thus obtained alloy powder.

18. A method of producing a Co-base target, which comprises: melting a Co-base alloy and an additive B (boron), whereby deoxidizing the Co-base alloy, subjecting the resultant Co-base alloy to a rapid cooling treatment to obtain a powder of the Co-base alloy, mixing the Co-base alloy powder and another metal powder, and sintering the thus obtained mixed powder.

19. A method of producing a Co-base target, which comprises: melting a Co-base alloy and an additive B (boron), whereby deoxidizing the Co-base alloy, subjecting the resultant Co-base alloy to a rapid cooling treatment to obtain a powder of the Co-base alloy, mixing the Co-base alloy powder and a metal powder of at least one element selected from the group consisting of Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and Pt, and sintering the thus obtained mixed powder.

20. A method of producing a Co-base target according to claim 17, 18, 19, which comprises: melting a Co-base alloy and an additive B (boron) in an amount of from more than 10 atomic % to 25 atomic %, whereby deoxidizing the Co-base alloy.

21. A method according to claim 18, wherein the thus obtained sintered product is subjected to a heat treatment.

22. A method according to claim 19, wherein the thus obtained sintered product is subjected to a heat treatment.

23. A method according to claim 17, wherein the rapid cooling treatment is conducted by the atomizing process.

24. A method according to claim 18, wherein the rapid cooling treatment is conducted by the atomizing process.

25. A method according to claim 19, wherein the rapid cooling treatment is conducted by the atomizing process.

26. A method according to claim 17, wherein the sintering is conducted by the Hot Isostatic Pressing method.

27. A method according to claim 18, wherein the sintering is conducted by the Hot Isostatic Pressing method.

28. A method according to claim 19, wherein the sintering is conducted by the Hot Isostatic Pressing method.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a Co-base target which is used to form a magnetic film of a magnetic recording medium for a magnetic disk device, etc., and a method of producing the Co-base target.

[0003] 2. Description of the Prior Art

[0004] Heretofore, a Co-base magnetic film has been developed so as to enable high density magnetic recording, and the addition of Pt and the like to the Co-base magnetic film has been performed. Such a Co-base magnetic film is usually formed by spattering. Furthermore, as disclosed in JP-B2-2806228, etc., a target produced by a melting/casting method has usually been used for this spattering.

[0005] In order to obtain the Co-base magnetic film, a target produced by powder sintering has been also proposed as disclosed in, for example, JP-A-3-138365.

[0006] In order to meet a recent request of a magnetic film having a high magnetic coercive force, it is necessary to contain a large amount of Pt, Cr, Ta and the like in addition to Co. In the case of the melting/casting process, as an amount of additive alloying elements increases, there arise problems of component segregation during casting and a difficulty in equalizing the metal structure of a cast material by plastic working. On the other hand, in the case of the powder-metallurgical method, there is an advantage that a metal structure in which the additive elements are uniformly dispersed can be obtained.

[0007] Further, there has been known a powder-metallurgical process according to which an elemental B (boron) is used in order to improve magnetic properties a sintered material, as disclosed in JP-A-5-263230.

[0008] However, a primary demerit of the powder-metallurgical method is that, since a material is processed in a powdery state, a much amount of oxygen is inevitably contained in the powdery material as compared to a cast material. From the viewpoint that the amount of oxygen should be reduced as much as possible rather than solving the problem of a non-uniform composition due to the component segregation since oxygen adversely affects on magnetic recording properties of the material, the powder-metallurgical method has not yet been used in a large scale.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide a novel Co-base target in which there can be inhibited an increase in the amount of oxygen which is the disadvantage of a powder sintering material capable of obtaining a uniform composition, and a method of producing the Co-base target.

[0010] The present inventors found that it is possible to produce a sintered target containing a low amount of oxygen by making the most of a deoxidizing effect of additive B (boron), whereby the present invention has been achieved.

[0011] More particularly, a novel target of the present invention is a Co-base target produced by powder sintering which comprises from more than 10 atomic % to 25 atomic % of B and not more than 100 ppm of oxygen.

[0012] Preferably, the target may comprise 30≧Pt≧5 atomic %, 30≧Cr≧10 atomic %, 10≧Ta>0 atomic % and/or 30≧Ni>0 atomic %. More preferably, the target may comprise from more than 0 (zero) to not more than 15 atomic % in total of one or more elements selected from the group consisting of Ti, Zr, Hf, V, Nb, Mo, W, Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and rare earth elements (REM).

[0013] The invention target can be obtained by a method of producing a Co-base target comprising the steps of melting a Co-base alloy together with an additive B (boron) in an amount of more than 10 to not more than 25 atomic % whereby deoxidizing the Co-base alloy, subjecting the resultant Co-base alloy to a rapid cooling treatment to obtain a powder, and sintering the resultant powder mixture to form a target of a sintered powder.

[0014] Alternatively, the invention target can be obtained by a method of producing a Co-base target comprising the steps of melting a Co-base alloy together with an additive B (boron) in an amount of more than 10 to not more than 25 atomic % whereby deoxidizing the Co-base alloy, subjecting the resultant Co-base alloy to a rapid cooling treatment to obtain a powder, mixing the powder with another metal powder, more particularly a metal powder consisting of one or more elements selected from the group consisting of Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and Pt, and sintering the resultant powder mixture to form a target of a sintered powder.

DESCRIPTION OF EMBODIMENTS

[0015] The key feature of the invention is that not more than 100 ppm of oxygen in the Co-base target produced by powder sintering has been realized which cannot be considered otherwise in the past. By virtue of the appropriate amount of B (boron), it has been possible to realize the invention target which is produced by powder sintering and contains a low amount of oxygen.

[0016] Since B (boron) has a high affinity with oxygen and a boron oxide is liable to sublimate, it is added to a molten metal when producing the powder by rapid cooling or when forming a master ingot (base alloy) to deoxidize the same with B in advance, whereby the oxygen amount of the powder produced by rapid cooling from a melt can be remarkably reduced.

[0017] In the present invention, it is preferable to sinter the powder obtained by rapid cooling and adjusted to have a desired target composition. Alternatively, in the case where the Co-base target material comprises an expensive additive such as Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and Pt, it is possible to mix the powder containing an additive alloying element of B (boron) obtained by rapid cooling with another metal powder consisting of one or more elements selected from the group consisting of Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and Pt, and to sinter the powder mixture. In the latter case, it is possible to optionally subject the sintered product to heat treatment or hot working in order to equalize the metal structure.

[0018] While there are an atomizing method, a spin melting method and so on, which are of producing a rapidly cooled powder, it is preferable to produce the powder by the gas atomizing method from the viewpoints of a packing density and a yield of the powder.

[0019] Furthermore, the sintering method includes a hot pressing method and a Hot Isostatic Pressing method (hereinafter referred to as HIP), but the HIP to which a high pressure can be applied is preferable from the viewpoint of a density of the sintered powder.

[0020] A preferable composition of the invention target may comprise an element(s) which can improve properties of the target material as a magnetic recording film. More particularly, the target material may comprise the elements of 25≧B>10 atomic %, 30≧Pt≧5 atomic %, 30≧Cr≧10 atomic %, 10≧Ta>0 atomic % and/or 30≧Ni>0 atomic %. It may be also comprise from more than 0 (zero) to not more than 15 atomic % in total of one or more elements selected from the group consisting of Ti, Zr, Hf, V, Nb, Mo, W, Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and rare earth elements. Needless to say, the invention target material is not limited to the above compositions.

[0021] Herein below there will be described effects of the additive alloying elements.

[0022] Additive B is the most important element of the present invention.

[0023] A spatter film produced by using a Co-base target of the invention is used as a magnetic layer of a magnetic recording medium in many cases. Conventionally, the magnetic layer in the magnetic recording medium has been formed with a single layer, and the magnetic layer has had to possess all properties such as a high coercive force and a high magnetic squareness ratio. For this reason, a Co-base film containing more than 10% of B as in the present invention has not been considered, because an increase of the coercive force cannot be expected.

[0024] However, at the present time, the magnetic layer consists of a plurality of layers. Thus, the magnetic layer has been modified so that different properties are required for the layers, respectively.

[0025] In the spatter film made of the Co-base target to which more than 10 atomic % of B is added as in the present invention, the increase in the coercive force cannot be desired as stated above, but the effect of reducing the noise of the spatter film is substantial. Moreover, when more than 10 to not more than 25 atomic % of B is added, the spatter film can possess an excellent effect of reducing oxygen.

[0026] However, the upper limit of the additive B is set to not more than 25 atomic % of B, because there noticeably appears an adverse influence that the spatter film becomes amorphous, if more than 25 atomic % of B is added. The oxygen reducing effect according to the invention can be attained by more than 10 atomic % of additive B (boron), which is preferable in order to obtain a target material containing not more than 100 ppm oxygen.

[0027] Pt can be added, since it increases the magnetic anisotropy by dissolving into Co and is effective to increase the coercive force of the film. Preferably, not less than 5 atomic % Pt is added in order to clearly increase the coercive force of the film. Further, since more than 30 atomic % of additive Pt remarkably deteriorates the inherent magnetic properties of Co, preferably Pt is added in an amount of 30≧Pt≧5 atomic %.

[0028] Cr segregates at grain boundaries in the film to make the grain boundaries non-magnetic whereby magnetically dividing ferromagnetic Co grains. When Cr is added in an amount of less than 10 atomic %, the magnetic division is not sufficient. On the other hand, when Cr is added in an amount of more than 30 atomic %, the magnetization of the film itself is deteriorated. Therefore, preferably Cr is added in an amount of 30≧Cr≧10 atomic %.

[0029] Ta has effects of refining crystal grains of the film and causing non-magnetic elements such as Cr to segregate at the grain boundaries. Such effects can be observed even if an additive Ta is small. On the other hand, it is not preferable to add an additive more than 10 atomic % of Ta because the magnetization of the film is deteriorated. Therefore, preferably Ta is added in an amount of 10≧Ta>0 atomic %.

[0030] Ni dissolves into Co to improve the magnetic anisotropy and the coercive force of the film. Ni can be added in an amount of not more than 30 atomic %. In order to increase the coercive force, Ni is added in an amount of not less than 5 atomic %, whereby a remarkable effect can be observed. An excess amount of more than 30 atomic % of Ni deteriorates inherent characteristics of Co. Thus, a preferable amount of Ni is 30≧Ni>0 atomic %, more preferably 30≧Ni≧5 atomic %.

[0031] Ti, Zr, Hf, V, Nb, Mo, W, Cu, Ag, Au, Ru, Rh, Pd, Os, Ir and rare earth elements (REM) are an element group having a common effect of improving magnetic properties of the film. Ti, Zr, Hf and rare earth elements have an effect of refining the crystal grains of the film; V and Nb have a similar effect to that of Ta; Mo and W have a similar effect to that of Cr; Cu, Ag and Au have an effect of dividing Co grains by virtue of segregation thereof at grain boundaries of the material; and Ru, Rh, Pd, Os and Ir have a similar effect to that of Pt. These elements are effective even if an additive amount thereof is small. When the total amount of the elements is more than 15 atomic %, the magnetic properties and crystallizing property of the film are deteriorated. Therefore, a total amount of them is preferably from more than zero to not more than 15 atomic %.

EXAMPLES

Example 1

[0032] Castings of some Co-base mother alloys were produced, wherein B (boron) was added during vacuum melting of the alloys in order to deoxidize the respective melt. The thus produced mother alloys were subjected to the gas atomization process to produce specimen powders of the invention examples. The chemical compositions of the powders are shown in Table 1. It is noted that the gas atomization was carried out in an Ar atmosphere. An average particle size and an oxygen amount of the respective atomized powders is shown in Table 1. It is noted that Specimens 5 and 10 of comparative examples shown in Table 1 were produced by the same process as those of the above invention examples except for not using additive B (boron) effective for deoxidization.

[0033] The thus produced atomized powders were sintered by the HIP method under conditions of 1000° C. (temperature), 100 MPa (pressure) and 3 h (time), and subsequently specimen targets each having φ101×5t (mm) (thickness) were produced by machining. Oxygen analysis values of the specimen targets are shown in Table 2.

[0034] As shown in Table 2, it can be understood that the specimen targets, each produced by sintering the atomized powder deoxidized by adding boron during melting, contain low amounts, especially not more than 100 ppm, of oxygen. 1

TABLE 1
Raw material powder
compositionAverage ParticleOxygen
Specimen(atomic %)Size (μm)(ppm)
1Co—20Cr—10Pt—11B4536
2Co—20Cr—10Pt—15B4234
3Co—20Cr—10Pt—20B4032
4Co—20Cr—10Pt—25B3830
5Co—20Cr—10Pt113118
6Co—20Cr—10Pt—2Ta—11B4039
7Co—20Cr—10Pt—2Ta—15B3838
8Co—20Cr—10Pt—2Ta—20B3737
9Co—20Cr—10Pt—2Ta—25B3533
10Co—20Cr—10Pt—2Ta101175

[0035] 2

TABLE 2
Target compositionO*
Specimen(atomic %)(ppm)Remarks
1Co—20Cr—10Pt—11B38Invention Example
2Co—20Cr—10Pt—15B37Invention Example
3Co—20Cr—10Pt—20B35Invention Example
4Co—20Cr—10Pt—25B33Invention Example
5Co—20Cr—10Pt124Comparative
Example
6Co—20Cr—10Pt—2Ta—11B42Invention Example
7Co—20Cr—10Pt—2Ta—15B41Invention Example
8Co—20Cr—10Pt—2Ta—20B40Invention Example
9Co—20Cr—10Pt—2Ta—25B37Invention Example
10Co—20Cr—10Pt—2Ta179Comparative
Example
*Note:
O = oxygen

Example 2

[0036] Gas atomized powders having chemical compositions shown in Table 3 were produced by the same manner as in Example 1, wherein the gas atomizing was carried out in an Ar atmosphere. An average particle size and an oxygen amount of the respective atomized powders produced is shown in Table 3. Furthermore, the average particle size and an oxygen amount of a Pt powder used is also shown in Table 3.

[0037] The Pt powder shown in Table 3 was added to the respective atomized powder produced, and they were mixed and sintered by the HIP method under the conditions of 1000° C. (temperature), 100 MPa (pressure) and 3 hours (time) to produce targets of φ101 (mm) (diameter) × 5 (mm) (thickness) having compositions shown in Table 4. Oxygen analysis values of the produced targets are shown in Table 4.

[0038] As shown in Table 4, it can be understood that the targets, produced by mixing the atomized powder deoxidized by adding boron during melting with a Pt powder, and sintering the powder mixture, contain low amounts, especially not more than 100 ppm, of oxygen. 3

TABLE 3
Raw material powderAv. ParticleOxygen
Specimencomposition (atomic %)Size (μm)(ppm)
21Co—22.2Cr—22.2B3530
22Co—22.2Cr—27.8B3228
23Co—22.2Cr115114
24Co—22.2Cr—2.2Ta—22.2B3736
25Co—22.2Cr—2.2Ta—27.8B3533
26Co—22.2Cr—2.2Ta97171
27Pure Pt131134
*Note:
Av. Particle Size = Average Particle Size

[0039] 4

TABLE 4
Target compositionO*
Specimen(atomic %)(ppm)Remarks
21Co—20Cr—10Pt—20B52Invention Example
22Co—20Cr—10Pt—25B49Invention Example
23Co—20Cr—10Pt136Comparative
Example
24Co—20Cr—10Pt—2Ta—20B56Invention Example
25Co—20Cr—10Pt—2Ta—25B55Invention Example
26Co—20Cr—10Pt—2Ta193Comparative
Example
*Note:
O = oxygen

Example 3

[0040] Gas atomized powders having chemical compositions shown in Table 5 were produced by the same manner as in Example 1, wherein the gas atomizing was carried out in an Ar atmosphere. An average particle size and an oxygen amount of the respective specimen atomized powders is shown in Table 5.

[0041] The atomized powders were sintered by the HIP method under conditions of 1000° C. (temperature), 100 MPa (pressure) and 3 hours (time) to produce specimen targets having φ101 (mm) (diameter) × 5 (mm) (thickness). Oxygen analysis values of the produced targets are shown in Table 6.

[0042] As shown in Table 6, it can be understood that the specimen targets, produced by sintering the atomized powder deoxidized by adding boron during melting, contain reduced amounts, especially not more than 100 ppm, of oxygen. 5

TABLE 5
Raw material powderAv. ParticleOxygen
Specimencomposition (atomic %)Size (μm)(ppm)
31Co—20Cr—10Pt—10Ni—15B4542
32Co—20Cr—10Pt—10Ni96125
33Co—20Cr—10Pt—5Ti—15B4151
34Co—20Cr—10Pt—5Ti89143
35Co—20Cr—10Pt—5Nb—15B4159
36Co—20Cr—10Pt—5Nb90155
37Co—20Cr—10Pt—5Mo—15B5145
38Co—20Cr—10Pt—5Mo108130
39Co—20Cr—10Pt—5Cu—15B5642
40Co—20Cr—10Pt—5Cu114130
50Co—20Cr—10Pt—5Ru—15B5347
51Co—20Cr—10Pt—5Ru111133
52Co—20Cr—10Pt—5Tb—15B3978
53Co—20Cr—10Pt—5Tb77192
*Note:
Av. Particle Size = Average Particle Size

[0043] 6

TABLE 6
Target compositionO*
Specimen(at %)(ppm)Remarks
31Co—20Cr—10Pt—10Ni—15B50Invention Ex.
32Co—20Cr—10Pt—10Ni135Comparative Ex.
33Co—20Cr—10Pt—5Ti—15B58Invention Ex.
34Co—20Cr—10Pt—5Ti149Comparative Ex.
35Co—20Cr—10Pt—5Nb—15B63Invention Ex.
36Co—20Cr—10Pt—5Nb156Comparative Ex.
37Co—20Cr—10Pt—5Mo—15B51Invention Ex.
38Co—20Cr—10Pt—5Mo137Comparative Ex.
39Co—20Cr—10Pt—5Cu—15B48Invention Ex.
40Co—20Cr—10Pt—5Cu136Comparative Ex.
50Co—20Cr—10Pt—5Ru—15B52Invention Ex.
51Co—20Cr—10Pt—5Ru137Comparative Ex.
52Co—20Cr—10Pt—5Tb—15B87Invention Ex.
53Co—20Cr—10Pt—5Tb201Comparative Ex.
*Note:
O = oxygen; Ex. = Example

Example 4

[0044] Specimen targets of Co-20Cr-10Pt-15B (at %) were produced by the producing processes shown in Table 7. Analysis values of impurity oxygen of the specimen targets are shown in Table 8.

[0045] Atomized powders were produced by the same method as in Examples 1 and 2. The sintering was conducted under conditions of 1000° C.×100 MPa×3 hours. The diffusion treatment of the sintered materials were conducted under conditions of 1100° C.×10 hours. The molten/cast material was obtained by melting under vacuum in an induction heating furnace and subsequently casting into a mold, whereby a specimen target of φ101×5t (mm) (thickness) was produced.

[0046] A board, wherein a Cr primer film was formed by spattering on an NiP plated Al board, was used, and the film was formed on the board with the Co-20Cr-10Pt-15B (at %) target of different production methods shown in Table 7 under conditions of 150° C. for the board temperature, 0.66 Pa for Ar pressure and 500 W DC for electric power. To investigate variations of the characteristics of magnetic film, a board formed with film was produced during a total forming time of 5 hours with one hour interval. Results of measurement of coercive force Hc measured by VSM (vibrating sample type magnetometer) are shown in Table 9, provided that Table 9 shows relative values taking the coercive force for one hour of Specimen 41 as 100.

[0047] It can be understood from Table 9 that, with regard to the respective invention specimen targets, the variation of forming film is small, that the higher the oxygen content of the specimen target is the lower the coercive force is, and that the variation of the melting/casting specimen target as time passes is slightly larger than those of the invention specimen targets. 7

TABLE 7
SpecimenProcessRemarks
41Co—20Cr—10Pt—15B (at %)Invention Example
atomized powder → sintering
42Co—22.2Cr—16.7B (at %)Invention Example
atomized powder + Pt
powder → sintering
43Co—22.2Cr—16.7B (at %)Invention Example
atomized powder + Pt
powder → sintering → diffusion
treatment
44Co—23.5Cr—11.8Pt (at %)Comparative Example
atomized powder + B
powder → sintering
45Melting and castingComparative Example
*Note:
at % = atomic %

[0048] 8

TABLE 8
SpecimenO* (ppm)Remarks
4136Invention Example
4253Invention Example
4353Invention Example
44185Comparative Example
4525Comparative Example
*Note:
O = oxygen

[0049] 9

TABLE 9
Coercive force (Hc)
FMTFMTFMTFMTFMT
Specimen1 hour2 hours3 hours4 hours5 hours
41100100100101100
421019910210099
431001009999100
448895909890
4510110010499103
*Note: FMT = Film Forming Time

[0050] According to the invention, it is possible to stably supply the Co-base target, having a uniform composition and a low oxygen amount, which can be used to produce a Co-base magnetic film for a magnetic recording medium for use in a magnetic disk device and the like. Thus, the invention is indispensable to manufacturing magnetic recording mediums.