# Patent

## Title
FePt-based sputtering target

## Abstract

An FePt-based sputtering target has a structure in which an FePt-based alloy phase, a C phase containing unavoidable impurities, and a metal oxide phase containing unavoidable impurities are mutually dispersed, the FePt-based alloy phase containing Pt in an amount of 40 at % or more and 60 at % or less with the balance being Fe and unavoidable impurities, wherein C is contained in an amount of more than 0 vol % and 20 vol % or less based on the total amount of the target, the metal oxide is contained in an amount of 10 vol % or more and less than 40 vol % based on the total amount of the target, and the total content of C and the metal oxide is 20 vol % or more and 40 vol % or less based on the total amount of the target.

## Background
This is a Continuation of International Application No. PCT/JP2013/050429 filed Jan. 11, 2013, which claims the benefit of Japanese Patent Application No. 2012-005695 filed Jan. 13, 2012. The disclosure of the prior applications is hereby incorporated by reference herein in its entirety.


TECHNICAL FIELD
The present invention relates to an FePt-based sputtering target and to a process for producing the same.
BACKGROUND ART
An FePt alloy can be provided with the fct (Ordered Face Centered Tetragonal) structure which has high crystal magnetic anisotropy by heat-treating at an elevated temperature (for example, at 600° C. or higher), and therefore an FePt alloy has been highlighted as a magnetic recording medium. To make FePt particles smaller and more uniform in the thin film of the FePt alloy, it is proposed that a predetermined quantity of carbon (C) be included into the thin film of the FePt alloy (for example, Patent Literature 1).
However, the formation method of the FePtC thin film, described in the Patent Literature 1, is the method of vapor-depositing Fe, Pt, and C simultaneously on an MgO (100) substrate by using the Fe target of a 2-inch diameter, C target of a 2-inch diameter, and the Pt target of 5 mm in height and width. In this method, it is difficult to obtain the film whose composition is controlled strictly. Additionally, three targets are required and each target needs a cathode, a power supply, etc, and so the cost of equipment becomes high while the preparatory work of sputtering takes time and effort.
It is thought that an FePtC thin film formed by the process for forming an FePtC thin film described in Patent Literature 1 has a granular structure in which FePt alloy particles are separated by partitions of C, thereby allowing the FePtC thin film to exhibit magnetic recording characteristics. However, when the partitions of the granular structure were formed only of C (carbon), a carbon phase 14 grew to surround FePt alloy particles 12 growing on a substrate surface 10A of a substrate 10, for example, as illustrated in FIG. 1. This sometimes prevented the FePt alloy particles 12 from growing vertically onto the substrate surface 10A so that a plurality of the FePt alloy particles 12 were deposited vertically onto the substrate surface 10A (for example, Non-Patent Literature 1). When a plurality of the FePt alloy particles 12 are deposited vertically onto the substrate surface 10A, the obtained thin film may have deteriorated characteristics as a magnetic recording medium, or may be useless as a magnetic recording medium.
In order to suppress the phenomenon that a plurality of the FePt alloy particles 12 are deposited vertically onto the substrate surface 10A, metal oxides such as Ta2O5 and TiO2 may be effectively used instead of C to form the partitions of the granular structure, which is disclosed in Non-Patent Literature 1.
CITATION LIST
Patent Literature


    Patent Literature 1: Japanese Patent No. 3950838


Non-Patent Literature


    Non-Patent Literature 1: J. S. Chen et al., Granular L10 FePt—X (X═C, TiO2, Ta2O5) (001) nanocomposite films with small grain size for high density magnetic recording, Journal of Applied Physics, American Institute of Physics, 2009, Volume: 105, Pages: 0713702-1 to 07B702-3.


SUMMARY OF INVENTION
Technical Problem
The present inventors have believed that C and a metal oxide are effectively used to form the partitions of the granular structure. To form the partitions of the granular structure not with only C but with C and a metal oxide, the process for forming an FePtC thin film described in Patent Literature 1 not only requires installation of three targets, Fe, Pt, and C into a sputtering device, but also requires installation of a metal oxide target into a sputtering device. This process takes more time and effort for preparation of sputtering and also increases the cost of the device.
The present invention has been made in view of the aforementioned problems. It is an object of the present invention to provide an FePt-based sputtering target which alone can form a thin film containing an FePt alloy, C, and a metal oxide and being usable as a magnetic recording medium, without using a plurality of targets, and a process for producing the same.
Solution to Problem
As a result of intensive research to solve the aforementioned problem, the present inventors found out that the aforementioned problem is solvable with the following FePt-based sputtering targets and solvable with the following processes for producing the FePt-based sputtering target, and the present inventors created the present invention.
Namely, an FePt-based sputtering target according to the present invention is an FePt-based sputtering target containing Fe, Pt, C, and a metal oxide, wherein the FePt-based sputtering target has a structure in which an FePt-based alloy phase, a C phase containing unavoidable impurities, and a metal oxide phase containing unavoidable impurities are mutually dispersed, the FePt-based alloy phase containing Pt in an amount of 40 at % or more and 60 at % or less with the balance being Fe and unavoidable impurities, and wherein C is contained in an amount of more than 0 vol % and 20 vol % or less based on a total amount of the target, the metal oxide is contained in an amount of 10 vol % or more and less than 40 vol % based on the total amount of the target, and a total content of C and the metal oxide is 20 vol % or more and 40 vol % or less based on the total amount of the target.
The phrase “an FePt-based alloy phase, a C phase containing unavoidable impurities, and a metal oxide phase containing unavoidable impurities are mutually dispersed” is a concept including a state in which the FePt-based alloy phase is a dispersion medium and the C phase and the metal oxide phase are dispersoids, and a state in which the C phase and the metal oxide phase are dispersion media and the FePt-based alloy phase is a dispersoid, and further including a state in which three phases, the FePt-based alloy phase, the C phase, and the metal oxide phase, are mixed with each other but it is not possible to determine which phase is a dispersion medium and which phase is a dispersoid.
In the present description, the FePt-based alloy means an alloy containing Fe and Pt as main components and includes not only a binary alloy containing only Fe and Pt but also ternary and higher alloys containing Fe and Pt as main components and an additional metal element(s) other than Fe and Pt. As used herein, the FePt-based sputtering target means a sputtering target containing Fe and Pt as main components and also includes sputtering targets containing, in addition to Fe and Pt, other metal component(s), an oxide, C, and the like.
In the present description, the phrase “α or more and β or less” may be described as “from α to β.”
The phase consisting of the C phase and the metal oxide phase preferably has an average size of 0.4 μm or less as determined by an intercept method.
A process for determining the average size of the phase consisting of the C phase and the metal oxide phase by the intercept method will be described below in the section of “DESCRIPTION OF EMBODIMENTS.”
The metal oxide may contain, for example, at least one of SiO2, TiO2, Ti2O3, Ta2O5, Cr2O3, CoO, Co3O4, B2O3, Fe2O3, CuO, Cu2O, Y2O3, MgO, Al2O3, ZrO2, Nb2O5, MoO3, CeO2, Sm2O3, Gd2O3, WO2, WO3, HfO2, and NiO2.
Preferably, the FePt-based sputtering target has a relative density of 90% or higher.
Some of the above-described FePt-based sputtering targets can be preferably used for a magnetic recording medium.
A process for producing an FePt-based sputtering target according to the present invention is a process for producing an FePt-based sputtering target, including: adding C powder containing unavoidable impurities and metal oxide powder containing unavoidable impurities to FePt-based alloy powder containing Pt in an amount of 40 at % or more and 60 at % or less with the balance being Fe and unavoidable impurities so that the C powder and the metal oxide powder are contained to satisfy:
0<α≦20;
10≦β<40; and
20≦α+β≦40,
where α and β represent contents of the C powder and the metal oxide powder by vol %, respectively, based on a total amount of the FePt-based alloy powder, the C powder, and the metal oxide powder, followed by mixing the FePt-based alloy powder, the C powder, and the metal oxide powder to produce a powder mixture; and molding the produced powder mixture while the powder mixture is heated under pressure.
In the production process, the phase consisting of the C phase and the metal oxide phase in the obtained FePt-based sputtering target has an average size of 0.4 with or less as determined by the intercept method.
In the production process, the metal oxide may contain, for example, at least one of SiO2, TiO2, Ti2O3, Ta2O5, Cr2O3, CoO, Co3O4, B2O3, Fe2O3, CuO, Cu2O, Y2O3, MgO, Al2O3, ZrO2, Nb2O5, MoO3, CeO2, Sm2O3, Gd2O3, WO2, WO3, HfO2, and NiO2.
The mixing to produce the powder mixture is preferably performed in an atmosphere in the presence of oxygen, and oxygen may be supplied to the atmosphere from outside of the atmosphere.
The oxygen may be supplied by supplying air. The use of air as the supply source of oxygen can reduce cost.
The atmosphere may be air. When the atmosphere is air, the cost can be reduced.
The atmosphere may not be air but may be an atmosphere composed substantially of an inert gas and oxygen. In this case, incorporation of impurities other than oxygen into the powder mixture during the mixing can be suppressed.
The concentration of oxygen in the atmosphere may be, for example, 10 vol % or higher and 30 vol % or lower.
The atmosphere may be released into the air during the mixing. In this case, even when the atmosphere is short of oxygen during the mixing, oxygen can be introduced from the air by releasing the atmosphere into the air, so that the shortage of oxygen can be mitigated.
Preferably, an atmosphere when the powder mixture is molded while heated under pressure is a vacuum or an inert gas atmosphere. In this manner, the amount of impurities in the obtained sintered product can be reduced.
Preferably, the FePt-based alloy powder is produced by an atomizing method, in terms of a reduction in the amount of impurities mixed. Preferably, the atomizing method is performed using argon gas or nitrogen gas, in terms of a further reduction in the amount of impurities mixed.
Some of the obtained FePt-based sputtering targets can be preferably used for a magnetic recording medium.
A second aspect of the FePt-based sputtering target according to the present invention is an FePt-based sputtering target produced by any one of the above production processes.
Advantageous Effects of Invention
The use of the FePt-based sputtering target according to the present invention allows formation of a thin film containing an FePt alloy, C, and a metal oxide and being usable as a magnetic recording medium with the single target alone, i.e., without using a plurality of targets.
Moreover, the FePt-based sputtering target according to the present invention contains not only a predetermined amount of C but also a predetermined amount of the metal oxide, so that a thin film obtained by sputtering and containing the FePt-based alloy is likely to have a favorable granular structure.
According to the process for producing an FePt-based sputtering target according to the present invention, FePt-based alloy powder, C powder, and metal oxide powder are mixed to produce a powder mixture, wherein Fe is mixed with the C powder and the metal oxide powder while being in the form of FePt-based alloy powder, i.e., an alloy of Fe and Pt. This can prevent oxidation of Fe during mixing from proceeding.
Furthermore, when the atmosphere contains oxygen during the production of the powder mixture, it can prevent the metal oxide powder from being reduced during mixing and thus can prevent incorporation of metal originated from the metal oxide powder into the FePt-based alloy powder during mixing. Therefore, an FePt-based thin film produced by using the obtained FePt-based sputtering target is likely to exhibit stable magnetic recording characteristics.
When the atmosphere contains oxygen during the production of the powder mixture, a certain amount of oxygen has already been adsorbed to the surface of C particles at the end of mixing even when the powder mixture contains C powder. Therefore, rapid adsorption of oxygen to the surface of the C particles and subsequent ignition of the C particles hardly occur even when a mixing container is opened to introduce the air after mixing, thereby allowing stable production even of the FePt-based sputtering target containing not only the metal oxide but also C.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an example of a problematic magnetic recording medium having a granular structure with partitions formed only of C (carbon).
FIG. 2 is a SEM photograph of a sintered product in Reference Example 1 (an image taken at a magnification of 1,000×; a bar scale in the photograph represents 10 μm).
FIG. 3 is a SEM photograph of a sintered product in Reference Example 1 (an image taken at a magnification of 3,000×; a bar scale in the photograph represents 1 μm).
FIG. 4 is a SEM photograph of a sintered product in Reference Example 1 (an image taken at a magnification of 5,000×; a bar scale in the photograph represents 1 μm).
FIG. 5 is a SEM photograph of a sintered product in Reference Example 1 (an image taken at a magnification of 10,000×; a bar scale in the photograph represents 1 μm).
FIG. 6 is a SEM photograph of a sintered product in Reference Example 2 (an image taken at a magnification of 1,000×; a bar scale in the photograph represents 10 μm).
FIG. 7 is a SEM photograph of a sintered product in Reference Example 2 (an image taken at a magnification of 3,000×; a bar scale in the photograph represents 1 μm).
FIG. 8 is a SEM photograph of a sintered product in Reference Example 2 (an image taken at a magnification of 5,000×; a bar scale in the photograph represents 1 μm).
FIG. 9 is a SEM photograph of a sintered product in Reference Example 2 (an image taken at a magnification of 10,000×; a bar scale in the photograph represents 1 μm).
FIG. 10 is a SEM photograph of a sintered product in Reference Example 3 (an image taken at a magnification of 1,000×; a bar scale in the photograph represents 10 μm).
FIG. 11 is a SEM photograph of a sintered product in Reference Example 3 (an image taken at a magnification of 3,000×; a bar scale in the photograph represents 1 μm).
FIG. 12 is a SEM photograph of a sintered product in Reference Example 3 (an image taken at a magnification of 5,000×; a bar scale in the photograph represents 1 μm).
FIG. 13 is a SEM photograph of a sintered product in Reference Example 3 (an image taken at a magnification of 10,000×; a bar scale in the photograph represents 1 μm).
FIG. 14 is a SEM photograph of a sintered product in Reference Example 4 (an image taken at a magnification of 1,000×; a bar scale in the photograph represents 10 μm).
FIG. 15 is a SEM photograph of a sintered product in Reference Example 4 (an image taken at a magnification of 3,000×; a bar scale in the photograph represents 1 μm).
FIG. 16 is a SEM photograph of a sintered product in Reference Example 4 (an image taken at a magnification of 5,000×; a bar scale in the photograph represents 1 μm).
FIG. 17 is a SEM photograph of a sintered product in Reference Example 4 (an image taken at a magnification of 10,000×; a bar scale in the photograph represents 1 μm).
FIG. 18 is a SEM photograph of a sintered product in Example 1 (an image taken at a magnification of 1,000×; a bar scale in the photograph represents 10 μm).
FIG. 19 is a SEM photograph of a sintered product in Example 1 (an image taken at a magnification of 3,000×; a bar scale in the photograph represents 1 μm).
FIG. 20 is a SEM photograph of a sintered product in Example 1 (an image taken at a magnification of 5,000×; a bar scale in the photograph represents 1 μm).
FIG. 21 is a SEM photograph of a sintered product in Example 1 (an image taken at a magnification of 10,000×; a bar scale in the photograph represents 1 μm).
FIG. 22 is a SEM photograph of a sintered product in Example 2 (an image taken at a magnification of 1,000×; a bar scale in the photograph represents 10 μm).
FIG. 23 is a SEM photograph of a sintered product in Example 2 (an image taken at a magnification of 3,000×; a bar scale in the photograph represents 1 μm).
FIG. 24 is a SEM photograph of a sintered product in Example 2 (an image taken at a magnification of 5,000×; a bar scale in the photograph represents 1 μm).
FIG. 25 is a SEM photograph of a sintered product in Example 2 (an image taken at a magnification of 10,000×; a bar scale in the photograph represents 1 μm).
FIG. 26 is a SEM photograph of a sintered product in Example 3 (an image taken at a magnification of 1,000×; a bar scale in the photograph represents 10 μm).
FIG. 27 is a SEM photograph of a sintered product in Example 3 (an image taken at a magnification of 3,000×; a bar scale in the photograph represents 1 μm).
FIG. 28 is a SEM photograph of a sintered product in Example 3 (an image taken at a magnification of 5,000×; a bar scale in the photograph represents 1 μm).
FIG. 29 is a SEM photograph of a sintered product in Example 3 (an image taken at a magnification of 10,000×; a bar scale in the photograph represents 1 μm).
FIG. 30 is a SEM photograph of a sintered product in Example 4 (an image taken at a magnification of 1,000×; a bar scale in the photograph represents 10 μm).
FIG. 31 is a SEM photograph of a sintered product in Example 4 (an image taken at a magnification of 3,000×; a bar scale in the photograph represents 1 μm).
FIG. 32 is a SEM photograph of a sintered product in Example 4 (an image taken at a magnification of 5,000×; a bar scale in the photograph represents 1 μm).
FIG. 33 is a SEM photograph of a sintered product in Example 4 (an image taken at a magnification of 10,000×; a bar scale in the photograph represents 1 μm).
FIG. 34 is a SEM photograph of a sintered product in Example 5 (an image taken at a magnification of 1,000×; a bar scale in the photograph represents 10 μm).
FIG. 35 is a SEM photograph of a sintered product in Example 5 (an image taken at a magnification of 3,000×; a bar scale in the photograph represents 1 μm).
FIG. 36 is a SEM photograph of a sintered product in Example 5 (an image taken at a magnification of 5,000×; a bar scale in the photograph represents 1 μm).
FIG. 37 is a SEM photograph of a sintered product in Example 5 (an image taken at a magnification of 10,000×; a bar scale in the photograph represents 1 μm).
FIG. 38 is a SEM photograph of a sintered product in Reference Example 5 (an image taken at a magnification of 3,000×; a bar scale in the photograph represents 1 μm).
FIG. 39 is a SEM photograph of a sintered product in Reference Example 5 (an image taken at a magnification of 5,000×; a bar scale in the photograph represents 1 μm).
FIG. 40 is a SEM photograph of a sintered product in Reference Example 5 (an image taken at a magnification of 10,000×; a bar scale in the photograph represents 1 μm).
FIG. 41 is a SEM photograph of a sintered product in Reference Example 6 (an image taken at a magnification of 1,000×; a bar scale in the photograph represents 10 μm).
FIG. 42 is a SEM photograph of a sintered product in Reference Example 6 (an image taken at a magnification of 3,000×; a bar scale in the photograph represents 1 μm).
FIG. 43 is a SEM photograph of a sintered product in Reference Example 6 (an image taken at a magnification of 5,000×; a bar scale in the photograph represents 1 μm).
FIG. 44 is a SEM photograph of a sintered product in Reference Example 6 (an image taken at a magnification of 10,000×; a bar scale in the photograph represents 1 μm).



DESCRIPTION OF EMBODIMENTS
Embodiments of the present invention will next be described in detail.
1. Components and Structure of Sputtering Target
An FePt-based sputtering target according to an embodiment of the present invention contains C (carbon) and a metal oxide in addition to alloy components (Fe, Pt).
Specifically, the FePt-based sputtering target according to the embodiment of the present invention contains Fe, Pt, C, and a metal oxide, wherein the FePt-based sputtering target has a structure in which an FePt alloy phase, a C phase containing unavoidable impurities, and a metal oxide phase containing unavoidable impurities are mutually dispersed, the FePt alloy phase containing Pt in an amount of 40 at % or more and 60 at % or less with the balance being Fe and unavoidable impurities, and wherein the volume fraction of C to the total amount of the target is more than 0 vol % and 20 vol % or less, the volume fraction of the metal oxide to the total amount of the target is 10 vol % or more and less than 40 vol %, and the total volume fraction of C and the metal oxide to the total amount of the target is 20 vol % or more and 40 vol % or less.
1-1. FePt Alloy
The FePt alloy can have an fct structure with high magnetocrystalline anisotropy when subjected to heat treatment at high temperature (e.g., 600° C. or higher). Therefore, the FePt alloy has a role in serving as a recording layer of a magnetic recording medium and is a main component of the FePt-based sputtering target according to the embodiment of the present invention.
The reason that the content of Pt in the FePt alloy phase is defined to be 40 at % or more and 60 at % or less in this embodiment is that, when the content of Pt in the FePt alloy phase is outside the range of 40 at % or more and 60 at % or less, the fct (ordered face centered tetragonal) structure may not appear. The content of Pt in the FePt alloy phase is preferably 45 at % or more and 55 at % or less, more preferably 49 at % or more and 51 at % or less, and particularly preferably 50 at %, from the viewpoint that the fct (ordered face centered tetragonal) structure appears reliably in the FePt alloy phase.
1-2. C and Metal Oxide
C and the metal oxide can form the partitions for separating the FePt alloy particles, which are magnetic particles, from each other in a layer containing the FePt alloy, C, and the metal oxide (hereinafter, may be referred to as an FePt—C-metal oxide layer) obtained by sputtering, and has a role in reducing and uniformizing the size of the FePt alloy particles in the FePt—C-metal oxide layer. C and the metal oxide are main components in the FePt-based sputtering target according to this embodiment.
In this embodiment, the content of C is more than 0 vol % and 20 vol % or less based on the total amount of the target, the content of the metal oxide is 10 vol % or more and less than 40 vol % based on the total amount of the target, and the total content of C and the metal oxide is 20 vol % or more and 40 vol % or less based on the total amount of the target.
The reason that the content of C is set to more than 0 vol % and 20 vol % or less based on the total amount of the target, the content of the metal oxide is set to 10 vol % or more and less than 40 vol % based on the total amount of the target, and the total content of C and the metal oxide is set to 20 vol % or more and 40 vol % or less based on the total amount of the target is that C and the metal oxide can form the partitions for separating the FePt alloy particles, which are magnetic particles, from each other in the FePt—C-metal oxide layer obtained by sputtering to achieve the effect of reducing and uniformizing the size of the FePt alloy particles. If the total content of C and the metal oxide is less than 20 vol %, this effect may not be sufficiently achieved. If the total content of C and the metal oxide is more than 40 vol %, the number of FePt alloy particles per unit volume of the FePt—C-metal oxide layer obtained by sputtering decreases, and this is disadvantageous for storage capacity.
The reason that the lower limit of the content of the metal oxide is set to 10 vol % based on the total amount of the target and the upper limit of the content of C is set to 20 vol % based on the total amount of the target is that, when the target contains a large amount of C and an insufficient amount of the metal oxide, C grows to surround the FePt alloy particles during sputtering. This may prevent the FePt alloy particles from growing vertically onto the substrate surface so that a plurality of the FePt alloy particles may be deposited vertically onto the substrate surface to deteriorate the characteristics as a magnetic recording medium. This can be avoided by containing 10 vol % or more (less than 40 vol %) of the metal oxide based on the total amount of the target and setting the upper limit of the content of C to 20 vol % based on the total amount of the target, making it possible to provide a favorable magnetic recording medium.
From the viewpoint of exhibiting the effect of reducing and uniformizing the size of the FePt particles in the FePt—C-metal oxide layer, from the viewpoint of the storage capacity of the FePt—C-metal oxide layer to be formed, and from the viewpoint of providing favorable characteristics as a magnetic recording medium, the content of C is preferably more than 0 vol % and 17 vol % or less based on the total amount of the target, the content of the metal oxide is preferably 13 vol % or more and less than 35 vol % based on the total amount of the target, and the total content of C and the metal oxide is preferably 25 vol % or more and 35 vol % or less based on the total amount of the target.
In this embodiment, the metal oxide may contain, for example, at least one of SiO2, TiO2, Ti2O3, Ta2O5, Cr2O3, CoO, Co3O4, B2O3, Fe2O3, CuO, Cu2O, Y2O3, MgO, Al2O3, ZrO2, Nb2O5, MoO3, CeO2, Sm2O3, Gd2O3, WO2, WO3, HfO2, and NiO2.
1-3. Structure of Target
The FePt-based sputtering target according to this embodiment has a structure in which the FePt alloy phase, the C phase containing unavoidable impurities, and the metal oxide phase containing unavoidable impurities are mutually dispersed, the FePt alloy phase containing Pt in an amount of 40 at % or more and 60 at % or less with the balance being Fe and unavoidable impurities, wherein the content of C is more than 0 vol % and 20 vol % or less based on the total amount of the target, the content of the metal oxide is 10 vol % or more and less than 40 vol % based on the total amount of the target, and the total content of C and the metal oxide is 20 vol % or more and 40 vol % or less based on the total amount of the target.
The reason that the FePt-based sputtering target according to this embodiment has the structure in which the FePt alloy phase, the C phase, and the metal oxide phase are mutually dispersed is to prevent certain regions from being sputtered at an excessive high rate during sputtering to improve the sputtering.
It is preferable to reduce the size of the C phase and the metal oxide phase in the target as much as possible, in order to reduce the difference in sputtering rate at different positions. Therefore, the average size of the phase consisting of the C phase and the metal oxide phase in the target is preferably 0.4 μm or less as determined by the intercept method, more preferably 0.35 μm or less, and particularly preferably 0.3 μm or less.
In order to reduce the average size of the C phase and the metal oxide phase in the target, the current size reduction technique requires extension of the time for mixing FePt alloy powder, C powder, and metal oxide powder. Therefore, it is unpractical to significantly reduce the average size of the C phase and the metal oxide phase in the target with the current size reduction technique in terms of production efficiency. When the average size of the C phase and the metal oxide phase in the target is smaller to a certain extent, the problem associated with the difference in sputtering rate at different positions does not particularly occur. Therefore, the lower limit may be set on the average size of the C phase and the metal oxide phase in the target. When the lower limit is set, in consideration of the cost of the current size reduction technique, the average size of the phase consisting of the C phase and the metal oxide phase in the target, as determined by the intercept method, is preferably from 0.1 to 0.4 μm, more preferably from 0.15 to 0.35 μm, and particularly preferably from 0.2 to 0.3 μm.
In the present description, the average size of the phase consisting of the C phase and the metal oxide phase is determined by the intercept method in the following manner. As used herein, the phase consisting of the C phase and the metal oxide phase refers to a phase picked out as the C phase and the metal oxide phase, not distinguishing between the C phase and the metal oxide phase and regarding them as a same phase.
First, two horizontal lines are drawn in a left-right direction on a SEM photograph of the cross section of the target taken at a magnification of 10,000× so that the image is divided vertically into three parts, and three vertical lines are drawn in a vertical direction so that the image is divided horizontally into four parts. As a result, a total of five lines are drawn on the SEM photograph of the cross section of the target taken at a magnification of 10,000×.
For each of the five lines, the total length of line segments intersecting the phase consisting of the C phase and the metal oxide phase are determined, and the number of the phase consisting of the C phase and the metal oxide phase intersected by the line are determined. Then the average of the lengths of the segments of the five lines that intersect the phase consisting of the C phase and the metal oxide phase is determined (by dividing the total length of the line segments intersecting the phase consisting of the C phase and the metal oxide phase by the number of the phases consisting of the C phase and the metal oxide phase intersected by the lines), and the obtained value is used as the average size of the phase consisting of the C phase and the metal oxide phase, determined by the intercept method.
In order to perform sputtering favorably, it is preferable that the relative density of the target be large because the larger the value of the relative density, the smaller the volume of voids in the target. More specifically, the relative density of the target is preferably 90% or higher. To increase the relative density of the target, it is preferable to mix the FePt alloy powder, the C powder, and the metal oxide powder sufficiently to reduce the particle size of the C powder and the metal oxide powder, as described later. The size of the C phase and the metal oxide phase in the target is thereby reduced, and the voids in the target can be filled by the plastic flow of the FePt alloy during sintering, so that the relative density increases.
The content of nitrogen is preferably 30 ppm by mass or less based on the total amount of the target. As the content of nitrogen in the target decreases, the content of nitrogen in the FePt—C-metal oxide layer to be obtained by sputtering also decreases, so that the FePt—C-metal oxide layer obtained is favorable.
2. Production Process
An FePt-based sputtering target according to the embodiment can be produced by: adding C powder containing unavoidable impurities and metal oxide powder containing unavoidable impurities to FePt alloy powder containing Pt in an amount of 40 at % or more and 60 at % or less with the balance being Fe and unavoidable impurities; mixing the FePt alloy powder, the C powder, and the metal oxide powder to produce a powder mixture; and then molding the produced powder mixture while the powder mixture is heated under pressure.
In this production process, Fe and Pt are supplied as the FePt alloy powder, and are not supplied as a single powder of Fe and a single powder of Pt. A single powder of Fe has high activity and may ignite in the air. However, when Fe is alloyed with Pt to form an FePt alloy powder, the activity of Fe can be reduced even in the form of powder. For this reason, this production process can suppress oxidation and ignition of Fe during mixing with the C powder and metal oxide powder, and/or oxidation and ignition of Fe when a mixing container is open to the air after mixing.
When the atmosphere contains oxygen during the production of the powder mixture, it can prevent the metal oxide powder from being reduced during mixing and thus can prevent incorporation of metal originated from the metal oxide powder into the FePt alloy powder during mixing. Therefore, an FePt-based thin film produced by using the obtained FePt-based sputtering target is likely to exhibit stable magnetic recording characteristics.
In this embodiment, the powder mixture contains C powder. When the atmosphere contains oxygen during the production of the powder mixture, a certain amount of oxygen is adsorbed to the surface of the C powder during mixing. Because a certain amount of oxygen has already been adsorbed to the surface of C particles, rapid adsorption of oxygen to the surface of the C particles and subsequent ignition of the C particles hardly occur even when a mixing container is opened to introduce the air during or after mixing, thereby allowing stable production even of the FePt-based sputtering target containing not only the metal oxide but also C.
2-1. Production of FePt Alloy Powder
No particular limitation is imposed on the process for producing the FePt alloy powder. However, in this embodiment, an atomizing method is performed using a molten FePt alloy containing Pt in an amount of 40 at % or more and 60 at % or less with the balance being Fe and unavoidable impurities to produce FePt alloy powder having the same composition as that of the molten FePt alloy.
When the FePt alloy powder contains Pt in an amount of 40 at % or more and 60 at % or less, the FePt alloy phase in the target obtained by sintering of the FePt alloy powder also contains Pt in an amount of 40 at % or more and 60 at % or less, so that the fct structure is more likely to appear in an FePt phase in an FePt—C-metal oxide layer obtained by sputtering using the above target.
Preferably, the FePt alloy powder is produced by an atomizing method. This is because of the following reason. In an atomizing method, raw metals (Fe and Pt) are first heated to high temperature to form molten metals. In this stage, alkali metals such as Na and K, alkaline-earth metals such as Ca, and gaseous impurities such as oxygen and nitrogen are volatilized and removed to the outside, so that the amount of impurities in the FePt alloy powder can be reduced. When a gas atomizing method is used, the amount of impurities in the FePt alloy powder can be further reduced by performing atomizing using argon gas or nitrogen gas.
The target obtained using the FePt alloy powder obtained by an atomizing method contains a reduced amount of impurities, so that the content of nitrogen can be suppressed to 30 mass ppm or less.
Therefore, sputtering performed using the target is favorable, and an FePt—C-metal oxide layer to be obtained is also favorable.
Examples of an applicable atomizing method include, for example, a gas atomizing method and a centrifugal atomizing method.
2-2. Mixing
The powder mixture is produced by mixing the FePt alloy powder obtained by the atomizing method with the C powder having an average particle diameter of, for example, from 20 to 100 nm so that the content of C is more than 0 vol % and 20 vol % or less based on the total amount of the powder mixture, and further with the metal oxide powder having an average particle diameter of, for example, from 20 to 100 nm so that the content of the metal oxide is 10 vol % or more and less than 40 vol % based on the total amount of the powder mixture. The total content of C and the metal oxide is 20 vol % or more and 40 vol % or less based on the total amount of the powder mixture.
When the atmosphere contains oxygen during the production of the powder mixture, it can prevent the metal oxide powder from being reduced during mixing and thus can prevent incorporation of metal originated from the metal oxide powder into the FePt alloy powder. An FePt-based thin film produced by using the obtained FePt-based sputtering target is likely to exhibit stable magnetic recording characteristics.
From the viewpoint of preventing the metal oxide powder from being reduced during mixing, it is preferable that oxygen be continuously supplied from the outside of the mixing container to the atmosphere during mixing. Continuous supply of oxygen hardly causes a shortage of oxygen in the atmosphere and easily prevents the metal oxide powder from being reduced during mixing.
Also, from the viewpoint of avoiding ignition of the C particles even when the mixing container is opened to introduce the air after mixing, it is preferable that oxygen be continuously supplied from the outside of the mixing container to the atmosphere during mixing.
However, if the amount of oxygen in the atmosphere during mixing of the FePt alloy powder, the C powder, and the metal oxide powder is too large, the powder mixture may contain an excess amount of oxygen during mixing and the C particles may ignite during mixing.
From the viewpoint of preventing the metal oxide powder from being reduced during mixing, from the viewpoint of avoiding ignition of the C particles even when the mixing container is opened to introduce the air after mixing, and from the viewpoint that the powder mixture may contain an excess amount of oxygen during mixing and the C particles may ignite during mixing if the amount of oxygen in the atmosphere is too large, the concentration of oxygen in the atmosphere during mixing is preferably from 10 to 30 vol %, more preferably from 15 to 25 vol %, particularly preferably 19 to 22 vol %.
Oxygen may be supplied to the atmosphere during mixing by supplying air. This can reduce cost.
The atmosphere during mixing may be composed substantially of an inert gas and oxygen. In this case, incorporation of impurities from the atmosphere into the powder mixture can be suppressed. For example, argon, nitrogen, etc. may be used as the inert gas.
The atmosphere during mixing may be released to the air at some point in the mixing step. Even when the atmosphere is short of oxygen at some point in the mixing step, oxygen can be introduced from the air by releasing the atmosphere into the air, so that the shortage of oxygen can be mitigated.
2-3. Molding Method
No particular limitation is imposed on the method for molding the powder mixture produced as described above while the powder mixture is heated under pressure. For example, a hot pressing method, a hot isostatic pressing method (HIP method), a spark plasma sintering method (SPS method), etc. may be used. Preferably, when implementing the present invention, such a molding method is performed in a vacuum or an inert gas atmosphere. In this case, even when the powder mixture contains a certain amount of oxygen (other than oxygen of the metal oxide), the amount of oxygen (other than oxygen of the metal oxide) in the obtained sintered product decreases. The amount of impurities such as nitrogen in the obtained sintered product also decreases.
3. Effects
When the target is produced by casting, it is difficult to increase the contents of C and the metal oxide because of the solid solution limit of C and the metal oxide in the alloy, separation of C and the metal oxide from the alloy due to the difference in specific gravity, and the like.
Whereas, the production process in this embodiment uses a sintering method and thus can increase the contents of C and the metal oxide based on the total amount of the target, making it possible to produce an FePt-based sputtering target in which the content of C is more than 0 vol % and 20 vol % or less based on the total amount of the target, the content of the metal oxide is 10 vol % or more and less than 40 vol % based on the total amount of the target, and the total content of C and the metal oxide is 20 vol % or more and 40 vol % or less based on the total amount of the target. Therefore, the use of the FePt-based sputtering target according to the embodiment for spattering allows formation of a thin film containing an FePt alloy and being usable as a magnetic recording medium with the single target alone, i.e., without using a plurality of targets.
In the production process in this embodiment, Fe is alloyed with Pt to form an FePt alloy powder, and thus the activity of Fe can be reduced even in the form of powder, thereby suppressing ignition and oxidation of Fe during mixing with the metal oxide powder.
When the atmosphere contains oxygen during the production of the powder mixture, it can prevent the metal oxide powder from being reduced during mixing and thus can prevent incorporation of metal originated from the metal oxide powder into the FePt alloy powder during mixing. Therefore, an FePt-based thin film produced by using the obtained FePt-based sputtering target is likely to exhibit stable magnetic recording characteristics.
In the production process in this embodiment, C powder is also used, and when the atmosphere contains oxygen during the production of the powder mixture, a certain amount of oxygen is adsorbed to the surface of the C powder during mixing. Because a certain amount of oxygen has already been adsorbed to the surface of the C particles, rapid adsorption of oxygen to the surface of the C particles and subsequent ignition of the C particles hardly occur even when the mixing container is opened to introduce the air after mixing, thereby allowing stable production even of the FePt-based sputtering target containing not only the metal oxide but also C.
EXAMPLES
Reference Example 1
The targeted composition of a powder mixture and a target in Reference Example 1 is (50Fe-50Pt)-30 vol % SiO2. More specifically, the targeted composition of the metal components is 50 at % Fe-50 at % Pt, and the targeted content of the metal oxide (SiO2) is 30 vol % based on the total amount of the target. When the content of the metal oxide (SiO2) is represented not by vol % but by mol %, the targeted composition of the powder mixture and the target in Reference Example 1 is (50Fe-50Pt)-11.27 mol % SiO2.
The metals in bulk form were weighed such that the composition of the alloy was Fe: 50 at % and Pt: 50 at % and then heated by high frequency heating to form a molten Fe—Pt alloy at 1,800° C. Then a gas atomizing method using argon gas was performed to produce 50 at % Fe-50 at % Pt alloy powder. The average particle diameter of the obtained alloy powder was measured using Microtrac MT3000 manufactured by NIKKISO Co., Ltd. and found to be 50 μm.
66.91 g of SiO2 powder having an average particle diameter of 0.7 μm and a bulk density of 2.20 g/cm3 was added to 1100.00 g of the obtained 50 at % Fe-50 at % Pt alloy powder such that the content of SiO2 was 30 vol % based on the total amount of the powders, and then these components were mixed using a ball mill until the cumulative number of revolutions reached 3,741,120 to thereby produce a powder mixture. Hereinafter, the cumulative number of revolutions of the ball mill may be referred to as the cumulative number of ball mill revolutions or simply as the number of revolutions.
During mixing, the mixing container was hermetically closed with a lid and filled with a gas mixture (Ar+O2), and under the atmosphere in the mixing container, the 50 at % Fe-50 at % Pt alloy powder and SiO2 powder were mixed.
When the cumulative number of ball mill revolutions reached 935,280, 1,870,560, 2,805,840 and 3,741,120, the mixing container was opened, and whether or not ignition had occurred was visually checked. However, no ignition was found at each point.
When the cumulative number of ball mill revolutions reached 1,870,560, 2,805,840, and 3,741,120, 30.00 g of the powder mixtures were subjected to hot pressing in a vacuum atmosphere at less than 20 Pa to produce disc-like sintered products having a diameter of 30 mm. The hot-pressing conditions (sintering temperature, sintering pressure, and sintering time) and the relative densities of the obtained sintered products are shown in TABLE 1 below. The theoretical density of the sintered product is 11.51 g/cm3.










TABLE 1









Relative



Cumulative

density


number of
Hot-pressing conditions
of












ball mill
Sintering
Sintering
Sintering
sintered



revolutions
temperature
pressure
time
product


(Number)
(° C.)
(MPa)
(min)
(%)
Ignition















935,280
—
—
—
—
—


1,870,560
1070
26.2
45
96.96
NO


2,805,840
1070
26.2
45
97.03
NO


3,741,120
1050
26.2
45
98.61
NO









The relative densities of the sintered products exceed 96%, and the amount of voids in the obtained sintered products was small.
The contents of oxygen and nitrogen in the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation. The contents of oxygen and nitrogen in the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation. The measurement results are shown in TABLE 2 below.











TABLE 2







Cumulative number





of ball mill



revolutions
Oxygen
Nitrogen



of 3,741,120
(mass %)
(mass ppm)









Powder mixture
3.36
42



Sintered product
3.21
19










The content of oxygen and the content of nitrogen in the sintered product both decrease compared to those in the powder mixture, while the degree of reduction in the content of oxygen is smaller than the degree of reduction in the content of nitrogen. This may be caused by the fact that the powder mixture and the sintered product both contain metal oxide SiO2.
The structure of the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 was observed under a scanning electron microscope (SEM). FIGS. 2 to 5 show SEM photographs of the sintered products. FIG. 2 is a SEM photograph taken at a magnification of 1,000× (a bar scale in the photograph represents 10 μm). FIG. 3 is a SEM photograph taken at a magnification of 3,000× (a bar scale in the photograph represents 1 μm). FIG. 4 is a SEM photograph taken at a magnification of 5,000× (a bar scale in the photograph represents 1 μm). FIG. 5 is a SEM photograph taken at a magnification of 10,000× (a bar scale in the photograph represents 1 μm). In FIGS. 2 to 5, black portions correspond to the SiO2 phase, and white portions correspond to the FePt alloy phase. As can be seen from FIGS. 2 to 5, fine regions of the SiO2 phase are dispersed in the entire area of the structure.
The average size of the SiO2 phase was determined by the intercept method based on the SEM photograph of FIG. 5 taken at a magnification of 10,000×.
Specifically, two horizontal lines were drawn in a left-right direction on the SEM photograph of FIG. 5 so that the image was divided vertically into three parts, and three vertical lines were drawn in a vertical direction so that the image was divided horizontally into four parts. Thus, a total of five lines are drawn on the SEM photograph of FIG. 5.
For each of the five lines, the total length of line segments intersecting the SiO2 phase and the number of the SiO2 phase intersected by the line were determined. Then the average of the lengths of the segments of the five lines that intersected the SiO2 phase was determined (by dividing the total length of the line segments intersecting the SiO2 phase by the number of the SiO2 phases intersected by the lines), and the obtained value was used as the average size of the SiO2 phase determined by the intercept method. The results showed that the average size of the SiO2 phase determined by the intercept method was 0.34 μm.
Reference Example 2
The targeted composition of a powder mixture and a target in Reference Example 2 is (50Fe-50Pt)-30 vol % TiO2. More specifically, the targeted composition of the metal components is 50 at % Fe-50 at % Pt, and the targeted content of the metal oxide (TiO2) is 30 vol % based on the total amount of the target. When the content of the metal oxide (TiO2) is represented not by vol % but by mol %, the targeted composition of the powder mixture and the target in Reference Example 2 is (50Fe-50Pt)-15.34 mol % TiO2.
To 1100.00 g of 50 at % Fe-50 at % Pt alloy powder produced in the same manner as in Reference Example 1, 126.85 g of TiO2 powder having an average particle diameter of 0.07 μm and a bulk density of 4.11 g/cm3 was added so that the content of TiO2 was 30 vol % based on the total amount of the powders. These components were then mixed with a ball mill until the cumulative number of revolutions reached 3,741,120 to produce a powder mixture.
During mixing, the mixing container was hermetically closed with a lid and filled with a gas mixture (Ar+O2), and under the atmosphere in the mixing container, the 50 at % Fe-50 at % Pt alloy powder and TiO2 powder were mixed.
When the cumulative number of ball mill revolutions reached 935,280, 1,870,560, 2,805,840 and 3,741,120, the mixing container was opened, and whether or not ignition had occurred was visually checked. However, no ignition was found at each point.
When the cumulative number of ball mill revolutions reached 1,870,560, 2,805,840, and 3,741,120, 30.00 g of the powder mixtures were subjected to hot pressing in a vacuum atmosphere at less than 20 Pa to produce disc-like sintered products having a diameter of 30 mm. The hot-pressing conditions (sintering temperature, sintering pressure, and sintering time) and the relative densities of the obtained sintered products are shown in TABLE 3 below. The theoretical density of the sintered product is 12.10 g/cm3.










TABLE 3









Relative



Cumulative

density


number of
Hot-pressing conditions
of












ball mill
Sintering
Sintering
Sintering
sintered



revolutions
temperature
pressure
time
product


(Number)
(° C.)
(MPa)
(min)
(%)
Ignition















935,280
—
—
—
—
—


1,870,560
1000
26.2
45
97.54
NO


2,805,840
960
26.2
45
96.97
NO


3,741,120
950
26.2
45
96.69
NO









The relative densities of the sintered products exceed 96%, and the amount of voids in the obtained sintered products was small.
The contents of oxygen and nitrogen in the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation. The contents of oxygen and nitrogen in the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation. The measurement results are shown in TABLE 4 below.











TABLE 4







Cumulative number





of ball mill



revolutions
Oxygen
Nitrogen



of 3,741,120
(mass %)
(mass ppm)









Powder mixture
4.52
46



Sintered product
3.96
31










The content of oxygen and the content of nitrogen in the sintered product both decrease compared to those in the powder mixture, while the degree of reduction in the content of oxygen is smaller than the degree of reduction in the content of nitrogen. This may be caused by the fact that the powder mixture and the sintered product both contain metal oxide TiO2.
The structure of the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 was observed under a scanning electron microscope (SEM). FIGS. 6 to 9 show SEM photographs of the sintered products. FIG. 6 is a SEM photograph taken at a magnification of 1,000× (a bar scale in the photograph represents 10 μm). FIG. 7 is a SEM photograph taken at a magnification of 3,000× (a bar scale in the photograph represents 1 μm). FIG. 8 is a SEM photograph taken at a magnification of 5,000× (a bar scale in the photograph represents 1 μm). FIG. 9 is a SEM photograph taken at a magnification of 10,000× (a bar scale in the photograph represents 1 μm). In FIGS. 6 to 9, black portions correspond to the TiO2 phase, and white portions correspond to the FePt alloy phase. As can be seen from FIGS. 6 to 9, fine regions of the TiO2 phase are dispersed in the entire area of the structure.
The average size of the TiO2 phase was determined by the intercept method based on the SEM photograph of FIG. 9 taken at a magnification of 10,000×. A specific method is the same as the method of Reference Example 1.
The results showed that the average size of the TiO2 phase determined by the intercept method was 0.28 μm.
Reference Example 3
The targeted composition of a powder mixture and a target in Reference Example 3 is (50Fe-50Pt)-36.63 vol % B2O3. More specifically, the targeted composition of the metal components is 50 at % Fe-50 at % Pt, and the targeted content of the metal oxide (B2O3) is 36.63 vol % based on the total amount of the target. When the content of the metal oxide (B2O3) is represented not by vol % but by mol %, the targeted composition of the powder mixture and the target in Reference Example 3 is (50Fe-50Pt)-11 mol % B2O3.
To 1100.00 g of 50 at % Fe-50 at % Pt alloy powder produced in the same manner as in Reference Example 1, 75.44 g of B2O3 powder was added so that the content of B2O3 was 36.63 vol % based on the total amount of the powders. These components were then mixed with a ball mill until the cumulative number of revolutions reached 5,736,960 to produce a powder mixture.
During mixing, the mixing container was hermetically closed with a lid and filled with a gas mixture (Ar+O2), and under the atmosphere in the mixing container, the 50 at % Fe-50 at % Pt alloy powder and B2O3 powder were mixed.
When the cumulative number of ball mill revolutions reached 935,280, 2,535,840, 4,136,400 and 5,736,960, the mixing container was opened, and whether or not ignition had occurred was visually checked. However, no ignition was found at each point.
When the cumulative number of ball mill revolutions reached 4,136,400 and 5,736,960, 30.00 g of the powder mixtures were subjected to hot pressing in a vacuum atmosphere at less than 20 Pa to produce disc-like sintered products having a diameter of 30 mm. The hot-pressing conditions (sintering temperature, sintering pressure, and sintering time) and the relative densities of the obtained sintered products are shown in TABLE 5 below. The theoretical density of the sintered product is 10.50 g/cm3. According to calculation based on the theoretical density of this sintered product of 10.50 g/cm3, the relative densities of the sintered products were 103.95% (cumulative number of ball mill revolutions: 4,136,400) and 105.22% (cumulative number of ball mill revolutions: 5,736,960) as shown in TABLE 5 below.










TABLE 5









Relative



Cumulative

density


number of
Hot-pressing conditions
of












ball mill
Sintering
Sintering
Sintering
sintered



revolutions
temperature
pressure
time
product


(Number)
(° C.)
(MPa)
(min)
(%)
Ignition















935,280
—
—
—
—
NO


2,535,840
—
—
—
—
NO


4,136,400
810
26.2
45
103.95
NO


5,736,960
840
26.2
45
105.22
NO









The relative densities of the sintered products exceed 100%, and the amount of voids in the obtained sintered products was small.
The contents of oxygen and nitrogen in the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 5,736,960 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation. The measurement results are shown in TABLE 6 below.











TABLE 6







Cumulative number





of ball mill



revolutions
Oxygen
Nitrogen



of 5,736,960
(mass %)
(mass ppm)









Sintered product
4.83
35










The contents of Fe, Pt, and B in the sintered product made of the powder mixture taken at a cumulative number of ball mill revolutions of 5,736,960 were analyzed by ICP. TABLE 7 below shows the analysis results as well as the contents of Fe, Pt, and B in the powder mixture before sintering. The contents of Fe, Pt, and B in the powder mixture before sintering are not the analysis results by ICP but the calculated values (theoretical values) based on the amounts of raw material powders blended for producing the powder mixture.












TABLE 7







Cumulative number






of ball mill



revolutions
Fe
Pt
B



of 5,736,960
(mass %)
(mass %)
(mass %)









Powder mixture
20.83
72.75
1.99



Sintered product
19.76
72.99
2.02










The structure of the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 5,736,960 was observed under a scanning electron microscope (SEM). FIGS. 10 to 13 show SEM photographs of the sintered products. FIG. 10 is a SEM photograph taken at a magnification of 1,000× (a bar scale in the photograph represents 10 μm). FIG. 11 is a SEM photograph taken at a magnification of 3,000× (a bar scale in the photograph represents 1 μm). FIG. 12 is a SEM photograph taken at a magnification of 5,000× (a bar scale in the photograph represents 1 μm). FIG. 13 is a SEM photograph taken at a magnification of 10,000× (a bar scale in the photograph represents 1 μm). In FIGS. 10 to 13, black portions correspond to the B2O3 phase, and gray portions correspond to the FePt alloy phase. As can be seen from FIGS. 10 to 13, fine regions of the B2O3 phase are dispersed in the entire area of the structure.
The average size of the B2O3 phase was determined by the intercept method based on the SEM photograph of FIG. 13 taken at a magnification of 10,000×. A specific method is the same as the method of Reference Example 1.
The results showed that the average size of the B2O3 phase determined by the intercept method was 0.22 μm.
Reference Example 4
The targeted composition of a powder mixture and a target in Reference Example 4 is (50Fe-50Pt)-12.07 vol % B2O3-24.68 vol % SiO2. That is, the targeted composition of metal components is 50 at % Fe-50 at % Pt; the targeted content of metal oxide B2O3 is 12.07 vol % based on the total amount of the target; and the targeted content of metal oxide SiO2 is 24.68 vol % based on the total amount of the target. When the contents of B2O3 and SiO2 are represented not by vol % but by mol %, the targeted composition of the powder mixture and the target in Reference Example 4 is (50Fe-50Pt)-3.53 mol % B2O3-10 mol % SiO2.
To 970.00 g of 50 at % Fe-50 at % Pt alloy powder produced in the same manner as in Reference Example 1, 21.97 g of B2O3 powder was added so that the content of B2O3 is 12.07 vol % based on the total amount of the powders, and 53.72 g of SiO2 powder having an average particle diameter of 0.7 μm and a bulk density of 2.20 g/cm3 was added so that the content of SiO2 was 24.68 vol % based on the total amount of the powders. These components were then mixed with a ball mill until the cumulative number of revolutions reached 3,852,360 to produce a powder mixture.
During mixing, the mixing container was hermetically closed with a lid and filled with a gas mixture (Ar+O2); and under the atmosphere in the mixing container, the 50 at % Fe-50 at % Pt alloy powder, the B2O3 powder, and the SiO2 powder were mixed.
When the cumulative number of ball mill revolutions reached 1,046,520, 1,981,800, 2,917,080 and 3,852,360, the mixing container was opened, and whether or not ignition had occurred was visually checked. However, no ignition was found at each point.
When the cumulative number of ball mill revolution reached 3,852,360, 30.00 g of the powder mixture was subjected to hot pressing in a vacuum atmosphere at less than 20 Pa to produce a disc-like sintered product having a diameter of 30 mm. The hot-pressing conditions (sintering temperature, sintering pressure, and sintering time) and the relative density of the obtained sintered product are shown in TABLE 8 below. If there is no difference between the amounts of B and Si contained in the powder mixture before sintering and those contained in the sintered product after sintering, the theoretical density of the sintered product is 10.57 g/cm3. As a result of the analysis of the sintered product by ICP, the content of B decreased by 0.01% by mass compared to the powder mixture before sintering, and the content of Si decreased by 0.04% by mass compared to the powder mixture before sintering (see, TABLE 10). Considering this and assuming that all B in the sintered product was B2O3 and all Si in the sintered product was SiO2, the theoretical density of the sintered product was calculated and found to be 10.59 g/cm3. Based on the theoretical density of this sintered product of 10.59 g/cm3, the relative density of the sintered product was calculated and found to be 100.38% as shown in TABLE 8 below.










TABLE 8









Relative



Cumulative

density


number of
Hot-pressing conditions
of












ball mill
Sintering
Sintering
Sintering
sintered



revolutions
temperature
pressure
time
product


(Number)
(° C.)
(MPa)
(min)
(%)
Ignition





1,046,520
—
—
—
—
NO


1,981,800
—
—
—
—
NO


2,917,080
—
—
—
—
NO


3,852,360
830
26.2
45
100.38
NO









The relative density of the sintered product was about 100%, and the amount of voids in the obtained sintered product was small. The relative density of the sintered product shown in TABLE 8 above is 100.38%, or over 100%. This is regarded as measurement error.
The contents of oxygen and nitrogen in the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,852,360 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation. The measurement results are shown in TABLE 9 below.











TABLE 9







Cumulative number





of ball mill



revolutions
Oxygen
Nitrogen



of 3,852,360
(mass %)
(mass ppm)









Sintered product
4.19
25










The contents of Fe, Pt, B, and Si in the sintered product made of the powder mixture taken at a cumulative number of ball mill revolutions of 3,852,360 were analyzed by ICP. TABLE 10 below shows the analysis results as well as the contents of Fe, Pt, B, and Si in the powder mixture before sintering.











TABLE 10





Cumulative






number of ball


mill revolutions
Fe
Pt
B
Si


of 3,852,360
(mass %)
(mass %)
(mass %)
(mass %)







Powder mixture
20.64
72.12
0.65
2.40


Sintered product
21.24
71.67
0.64
2.36









The structure of the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,852,360 was observed under a scanning electron microscope (SEM). FIGS. 14 to 17 show SEM photographs of the sintered products. FIG. 14 is a SEM photograph taken at a magnification of 1,000× (a bar scale in the photograph represents 10 μm). FIG. 15 is a SEM photograph taken at a magnification of 3,000× (a bar scale in the photograph represents 1 μm). FIG. 16 is a SEM photograph taken at a magnification of 5,000× (a bar scale in the photograph represents 1 μm). FIG. 17 is a SEM photograph taken at a magnification of 10,000× (a bar scale in the photograph represents 1 μm). In FIGS. 14 to 17, black portions correspond to the metal oxide phase (the B2O3 phase and the SiO2 phase), and gray portions correspond to the FePt alloy phase. As can be seen from FIGS. 14 to 17, fine regions of the metal oxide phase (the B2O3 phase and the SiO2 phase) are dispersed in the entire area of the structure.
The average size of the metal oxide phase (the phase consisting of the B2O3 phase and the SiO2 phase) was determined by the intercept method based on the SEM photograph of FIG. 17 taken at a magnification of 10,000×. A specific method is the same as the method of Reference Example 1.
The results showed that the average size of the metal oxide phase (the phase consisting of the B2O3 phase and the SiO2 phase) determined by the intercept method was 0.27 μm.
Example 1
The targeted composition of a powder mixture and a target in Example 1 is (50Fe-50Pt)-6 vol % C-24 vol % SiO2. That is, the targeted composition of metal components is 50 at % Fe-50 at % Pt; the targeted content of C is 6 vol % based on the total amount of the target; and the targeted content of metal oxide (SiO2) is 24 vol % based on the total amount of the target. When the contents of C and metal oxide (SiO2) are represented not by vol % but by mol %, the targeted composition of the powder mixture and the target in Example 1 is (50Fe-50Pt)-10.60 mol % C-8.25 mol % SiO2.
To 1100.00 g of 50 at % Fe-50 at % Pt alloy powder produced in the same manner as in Reference Example 1, 13.72 g of C powder having an average particle diameter of 35 μm and a bulk density of 0.25 g/cm3 was added so that the content of C is 5.7 vol % based on the total amount of the powders, and 53.44 g of SiO2 powder having an average particle diameter of 0.7 μm and a bulk density of 2.20 g/cm3 was added so that the content of SiO2 was 23.4 vol % based on the total amount of the powders. These components were then mixed with a ball mill until the cumulative number of revolutions reached 3,741,120 to produce a powder mixture.
During mixing, the mixing container was hermetically closed with a lid and filled with a gas mixture (Ar+O2); and under the atmosphere in the mixing container, the 50 at % Fe-50 at % Pt alloy powder, the C powder, and the SiO2 powder were mixed.
When the cumulative number of ball mill revolutions reached 935,280, 1,870,560, 2,805,840 and 3,741,120, the mixing container was opened, and whether or not ignition had occurred was visually checked. However, no ignition was found at each point.
When the cumulative number of ball mill revolution reached 3,741,120, 30.00 g of the powder mixture was subjected to hot pressing in a vacuum atmosphere at less than 20 Pa to produce a disc-like sintered product having a diameter of 30 mm. The hot-pressing conditions (sintering temperature, sintering pressure, and sintering time) and the relative density of the obtained sintered product are shown in TABLE 11 below. The theoretical density of the sintered product is 11.51 g/cm3, which is calculated in consideration of a reduction in the amount of carbon during mixing and sintering (i.e., calculated using the content of carbon in the sintered product shown in TABLE 12). Based on this theoretical density, the relative density of the sintered product was calculated.










TABLE 11









Relative



Cumulative

density


number of
Hot-pressing conditions
of












ball mill
Sintering
Sintering
Sintering
sintered



revolutions
temperature
pressure
time
product


(Number)
(° C.)
(MPa)
(min)
(%)
Ignition















935,280
—
—
—
—
NO


1,870,560
—
—
—
—
NO


2,805,840
—
—
—
—
NO


3,741,120
1270
24.5
45
97.31
NO









The relative density of the sintered product exceeds 97%, and the amount of voids in the obtained sintered product was small.
The contents of oxygen and nitrogen in the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation, and the content of carbon was measured using a Carbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The contents of oxygen and nitrogen in the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation, and the content of carbon was measured using a Carbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The measurement results are shown in TABLE 12 below.












TABLE 12







Cumulative number






of ball mill



revolutions
Oxygen
Nitrogen
Carbon



of 3,741,120
(mass %)
(mass ppm)
(mass %)





















Powder mixture
1.56
130
3.27



Sintered product
1.06
10
2.18










The content of oxygen and the content of nitrogen in the sintered product both decrease compared to those in the powder mixture, while the degree of reduction in the content of oxygen is smaller than the degree of reduction in the content of nitrogen. This may be caused by the fact that the powder mixture and the sintered product both contain metal oxide SiO2.
As comparing the content of oxygen and the content of nitrogen in the sintered product with those in the powder mixture, the degree of reduction in the content of oxygen and the content of nitrogen due to sintering in Example 1 is larger than that in Reference Examples 1 and 2. This may be because the powder mixture of Example 1 contains the C powder and thus oxygen and nitrogen have been adsorbed to the surface of the C powder.
The structure of the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 was observed under a scanning electron microscope (SEM). FIGS. 18 to 21 show SEM photographs of the sintered products. FIG. 18 is a SEM photograph taken at a magnification of 1,000× (a bar scale in the photograph represents 10 μm). FIG. 19 is a SEM photograph taken at a magnification of 3,000× (a bar scale in the photograph represents 1 μm). FIG. 20 is a SEM photograph taken at a magnification of 5,000× (a bar scale in the photograph represents 1 μm). FIG. 21 is a SEM photograph taken at a magnification of 10,000× (a bar scale in the photograph represents 1 μm). In FIGS. 18 to 21, black portions correspond to the C phase and the SiO2 phase, and white portions correspond to the FePt alloy phase. As can be seen from FIGS. 18 to 21, fine regions of the C phase and the SiO2 phase are dispersed in the entire area of the structure.
The average size of the phase consisting of the C phase and the SiO2 phase was determined by the intercept method based on the SEM photograph of FIG. 21 taken at a magnification of 10,000×. A specific method is the same as the method of Reference Example 1. As used herein, the phase consisting of the C phase and the SiO2 phase refers to a phase picked out as the C phase and the SiO2 phase, not distinguishing between the C phase and the SiO2 phase and regarding them as a same phase.
The results showed that the average size of the phase consisting of the C phase and the SiO2 phase determined by the intercept method was 0.28 μm.
Example 2
The targeted composition of a powder mixture and a target in Example 2 is (50Fe-50Pt)-9 vol % C-21 vol % SiO2. That is, the targeted composition of metal components is 50 at % Fe-50 at % Pt; the targeted content of C is 9 vol % based on the total amount of the target; and the targeted content of metal oxide (SiO2) is 21 vol % based on the total amount of the target. When the contents of C and metal oxide (SiO2) are represented not by vol % but by mol %, the targeted composition of the powder mixture and the target in Example 2 is (50Fe-50Pt)-15.24 mol % C-6.92 mol % SiO2.
To 1100.00 g of 50 at % Fe-50 at % Pt alloy powder produced in the same manner as in Reference Example 1, 20.57 g of C powder having an average particle diameter of 35 μm and a bulk density of 0.25 g/cm3 was added so that the content of C is 8.8 vol % based on the total amount of the powders, and 47.73 g of SiO2 powder having an average particle diameter of 0.7 μm and a bulk density of 2.20 g/cm3 was added so that the content of SiO2 was 21.2 vol % based on the total amount of the powders. These components were then mixed with a ball mill until the cumulative number of revolutions reached 3,741,120 to produce a powder mixture.
During mixing, the mixing container was hermetically closed with a lid and filled with a gas mixture (Ar+O2); and under the atmosphere in the mixing container, the 50 at % Fe-50 at % Pt alloy powder, the C powder, and the SiO2 powder were mixed.
When the cumulative number of ball mill revolutions reached 935,280, 1,870,560, 2,805,840 and 3,741,120, the mixing container was opened, and whether or not ignition had occurred was visually checked. However, no ignition was found at each point.
When the cumulative number of ball mill revolution reached 3,741,120, 30.00 g of the powder mixture was subjected to hot pressing in a vacuum atmosphere at less than 20 Pa to produce a disc-like sintered product having a diameter of 30 mm. The hot-pressing conditions (sintering temperature, sintering pressure, and sintering time) and the relative density of the obtained sintered product are shown in TABLE 13 below. The theoretical density of the sintered product is 11.51 g/cm3, which is calculated in consideration of a reduction in the amount of carbon during mixing and sintering (i.e., calculated using the content of carbon in the sintered product shown in TABLE 14). Based on this theoretical density, the relative density of the sintered product was calculated.










TABLE 13









Relative



Cumulative

density


number of
Hot-pressing conditions
of












ball mill
Sintering
Sintering
Sintering
sintered



revolutions
temperature
pressure
time
product


(Number)
(° C.)
(MPa)
(min)
(%)
Ignition















935,280
—
—
—
—
NO


1,870,560
—
—
—
—
NO


2,805,840
—
—
—
—
NO


3,741,120
1280
24.5
45
97.50
NO









The relative density of the sintered product exceeds 97%, and the amount of voids in the obtained sintered product was small.
The contents of oxygen and nitrogen in the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation, and the content of carbon was measured using a Carbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The contents of oxygen and nitrogen in the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation, and the content of carbon was measured using a Carbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The measurement results are shown in TABLE 14 below.












TABLE 14







Cumulative number






of ball mill



revolutions
Oxygen
Nitrogen
Carbon



of 3,741,120
(mass %)
(mass ppm)
(mass %)





















Powder mixture
3.50
164
2.31



Sintered product
1.95
5
1.76










The content of oxygen and the content of nitrogen in the sintered product both decrease compared to those in the powder mixture, while the degree of reduction in the content of oxygen is smaller than the degree of reduction in the content of nitrogen. This may be caused by the fact that the powder mixture and the sintered product both contain metal oxide SiO2.
As comparing the content of oxygen and the content of nitrogen in the sintered product with those in the powder mixture, the degree of reduction in the content of oxygen and the content of nitrogen due to sintering in Example 2 is larger than that in Reference Examples 1 and 2. This may be because the powder mixture of Example 2 contains the C powder and thus oxygen and nitrogen have been adsorbed to the surface of the C powder.
The structure of the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 was observed under a scanning electron microscope (SEM). FIGS. 22 to 25 show SEM photographs of the sintered products. FIG. 22 is a SEM photograph taken at a magnification of 1,000× (a bar scale in the photograph represents 10 μm). FIG. 23 is a SEM photograph taken at a magnification of 3,000× (a bar scale in the photograph represents 1 μm). FIG. 24 is a SEM photograph taken at a magnification of 5,000× (a bar scale in the photograph represents 1 μm). FIG. 25 is a SEM photograph taken at a magnification of 10,000× (a bar scale in the photograph represents 1 μm). In FIGS. 22 to 25, black portions correspond to the C phase and the SiO2 phase, and white portions correspond to the FePt alloy phase. As can be seen from FIGS. 22 to 25, fine regions of the C phase and the SiO2 phase are dispersed in the entire area of the structure.
The average size of the phase consisting of the C phase and the SiO2 phase was determined by the intercept method based on the SEM photograph of FIG. 25 taken at a magnification of 10,000×. A specific method is the same as the method of Reference Example 1. As used herein, the phase consisting of the C phase and the SiO2 phase refers to a phase picked out as the C phase and the SiO2 phase, not distinguishing between the C phase and the SiO2 phase and regarding them as a same phase.
The results showed that the average size of the phase consisting of the C phase and the SiO2 phase determined by the intercept method was 0.23 μm.
Example 3
The targeted composition of a powder mixture and a target in Example 3 is (50Fe-50Pt)-12 vol % C-18 vol % SiO2. That is, the targeted composition of metal components is 50 at % Fe-50 at % Pt; the targeted content of C is 12 vol % based on the total amount of the target; and the targeted content of metal oxide (SiO2) is 18 vol % based on the total amount of the target. When the contents of C and metal oxide (SiO2) are represented not by vol % but by mol %, the targeted composition of the powder mixture and the target in Example 3 is (50Fe-50Pt)-19.53 mol % C-5.70 mol % SiO2.
To 1100.00 g of 50 at % Fe-50 at % Pt alloy powder produced in the same manner as in Reference Example 1, 27.44 g of C powder having an average particle diameter of 35 μm and a bulk density of 0.25 g/cm3 was added so that the content of C is 12 vol % based on the total amount of the powders, and 40.07 g of SiO2 powder having an average particle diameter of 0.7 μm and a bulk density of 2.20 g/cm3 was added so that the content of SiO2 was 18 vol % based on the total amount of the powders. These components were then mixed with a ball mill until the cumulative number of revolutions reached 3,741,120 to produce a powder mixture.
During mixing, the mixing container was hermetically closed with a lid and filled with a gas mixture (Ar+O2); and under the atmosphere in the mixing container, the 50 at % Fe-50 at % Pt alloy powder, the C powder, and the SiO2 powder were mixed.
When the cumulative number of ball mill revolutions reached 935,280, 1,870,560, 2,805,840 and 3,741,120, the mixing container was opened, and whether or not ignition had occurred was visually checked. However, no ignition was found at each point.
When the cumulative number of ball mill revolution reached 3,741,120, 30.00 g of the powder mixture was subjected to hot pressing in a vacuum atmosphere at less than 20 Pa to produce a disc-like sintered product having a diameter of 30 mm. The hot-pressing conditions (sintering temperature, sintering pressure, and sintering time) and the relative density of the obtained sintered product are shown in TABLE 15 below. The theoretical density of the sintered product is 11.52 g/cm3, which is calculated in consideration of a reduction in the amount of carbon during mixing and sintering (i.e., calculated using the content of carbon in the sintered product shown in TABLE 16). Based on this theoretical density, the relative density of the sintered product was calculated.










TABLE 15









Relative



Cumulative

density


number of
Hot-pressing conditions
of












ball mill
Sintering
Sintering
Sintering
sintered



revolutions
temperature
pressure
time
product


(Number)
(° C.)
(MPa)
(min)
(%)
Ignition 















935,280
—
—
—
—
NO


1,870,560
—
—
—
—
NO


2,805,840
—
—
—
—
NO


3,741,120
1300
24.5
45
96.68
NO









The relative density of the sintered product exceeds 96%, and the amount of voids in the obtained sintered product was small.
The contents of oxygen and nitrogen in the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation, and the content of carbon was measured using a Carbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The contents of oxygen and nitrogen in the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation, and the content of carbon was measured using a Carbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The measurement results are shown in TABLE 16 below.












TABLE 16







Cumulative number






of ball mill



revolutions
Oxygen
Nitrogen
Carbon



of 3,741,120
(mass %)
(mass ppm)
(mass %)





















Powder mixture
3.26
209
3.12



Sintered product
1.79
10
2.47










The content of oxygen and the content of nitrogen in the sintered product both decrease compared to those in the powder mixture, while the degree of reduction in the content of oxygen is smaller than the degree of reduction in the content of nitrogen. This may be caused by the fact that the powder mixture and the sintered product both contain metal oxide SiO2.
As comparing the content of oxygen and the content of nitrogen in the sintered product with those in the powder mixture, the degree of reduction in the content of oxygen and the content of nitrogen due to sintering in Example 3 is larger than that in Reference Examples 1 and 2. This may be because the powder mixture of Example 3 contains the C powder and thus oxygen and nitrogen have been adsorbed to the surface of the C powder.
The structure of the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 was observed under a scanning electron microscope (SEM). FIGS. 26 to 29 show SEM photographs of the sintered products. FIG. 26 is a SEM photograph taken at a magnification of 1,000× (a bar scale in the photograph represents 10 μm). FIG. 27 is a SEM photograph taken at a magnification of 3,000× (a bar scale in the photograph represents 1 μm). FIG. 28 is a SEM photograph taken at a magnification of 5,000× (a bar scale in the photograph represents 1 μm). FIG. 29 is a SEM photograph taken at a magnification of 10,000× (a bar scale in the photograph represents 1 μm). In FIGS. 26 to 29, black portions correspond to the C phase and the SiO2 phase, and white portions correspond to the FePt alloy phase. As can be seen from FIGS. 26 to 29, fine regions of the C phase and the SiO2 phase are dispersed in the entire area of the structure.
The average size of the phase consisting of the C phase and the SiO2 phase was determined by the intercept method based on the SEM photograph of FIG. 29 taken at a magnification of 10,000×. A specific method is the same as the method of Reference Example 1. As used herein, the phase consisting of the C phase and the SiO2 phase refers to a phase picked out as the C phase and the SiO2 phase, not distinguishing between the C phase and the SiO2 phase and regarding them as a same phase.
The results showed that the average size of the phase consisting of the C phase and the SiO2 phase determined by the intercept method was 0.30 μm.
Example 4
The targeted composition of a powder mixture and a target in Example 4 is (50Fe-50Pt)-15 vol % C-15 vol % SiO2. That is, the targeted composition of metal components is 50 at % Fe-50 at % Pt; the targeted content of C is 15 vol % based on the total amount of the target; and the targeted content of metal oxide (SiO2) is 15 vol % based on the total amount of the target. When the contents of C and metal oxide (SiO2) are represented not by vol % but by mol %, the targeted composition of the powder mixture and the target in Example 4 is (50Fe-50Pt)-23.48 mol % C-4.57 mol % SiO2.
To 1100.00 g of 50 at % Fe-50 at % Pt alloy powder produced in the same manner as in Reference Example 1, 34.37 g of C powder having an average particle diameter of 35 μm and a bulk density of 0.25 g/cm3 was added so that the content of C is 15 vol % based on the total amount of the powders, and 33.46 g of SiO2 powder having an average particle diameter of 0.7 μm and a bulk density of 2.20 g/cm3 was added so that the content of SiO2 was 15 vol % based on the total amount of the powders. These components were then mixed with a ball mill until the cumulative number of revolutions reached 3,741,120 to produce a powder mixture.
During mixing, the mixing container was hermetically closed with a lid and filled with a gas mixture (Ar+O2); and under the atmosphere in the mixing container, the 50 at % Fe-50 at % Pt alloy powder, the C powder, and the SiO2 powder were mixed.
When the cumulative number of ball mill revolutions reached 935,280, 1,870,560, 2,805,840 and 3,741,120, the mixing container was opened, and whether or not ignition had occurred was visually checked. However, no ignition was found at each point.
When the cumulative number of ball mill revolution reached 1,870,560, 2,805,840 and 3,741,120, 30.00 g of the powder mixture was subjected to hot pressing in a vacuum atmosphere at less than 20 Pa to produce a disc-like sintered product having a diameter of 30 mm. The hot-pressing conditions (sintering temperature, sintering pressure, and sintering time) and the relative density of the obtained sintered product are shown in TABLE 17 below. The theoretical density of the sintered product is 11.51 g/cm3, which is calculated in consideration of a reduction in the amount of carbon during mixing and sintering (i.e., calculated using the content of carbon in the sintered product shown in TABLE 18). Based on this theoretical density, the relative density of the sintered product (sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120) was calculated.










TABLE 17









Relative



Cumulative

density


number of
Hot-pressing conditions
of












ball mill
Sintering
Sintering
Sintering
sintered



revolutions
temperature
pressure
time
product


(Number)
(° C.)
(MPa)
(min)
(%)
Ignition















935,280
—
—
—
—
NO


1,870,560
1370
26.2
45
—
NO


2,805,840
1300
26.2
45
—
NO


3,741,120
1290
26.2
45
95.81
NO









The relative density of the sintered product exceeds 95%, and the amount of voids in the obtained sintered product was small.
The contents of oxygen and nitrogen in the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation, and the content of carbon was measured using a Carbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The contents of oxygen and nitrogen in the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation, and the content of carbon was measured using a Carbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The measurement results are shown in TABLE 18 below.












TABLE 18







Cumulative number






of ball mill



revolutions
Oxygen
Nitrogen
Carbon



of 3,741,120
(mass %)
(mass ppm)
(mass %)





















Powder mixture
3.22
186
2.87



Sintered product
1.39
6
2.24










The content of oxygen and the content of nitrogen in the sintered product both decrease compared to those in the powder mixture, while the degree of reduction in the content of oxygen is smaller than the degree of reduction in the content of nitrogen. This may be caused by the fact that the powder mixture and the sintered product both contain metal oxide SiO2.
As comparing the content of oxygen and the content of nitrogen in the sintered product with those in the powder mixture, the degree of reduction in the content of oxygen and the content of nitrogen due to sintering in Example 4 is larger than that in Reference Examples 1 and 2. This may be because the powder mixture of Example 4 contains the C powder and thus oxygen and nitrogen have been adsorbed to the surface of the C powder.
The structure of the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 was observed under a scanning electron microscope (SEM). FIGS. 30 to 33 show SEM photographs of the sintered products. FIG. 30 is a SEM photograph taken at a magnification of 1,000× (a bar scale in the photograph represents 10 μm). FIG. 31 is a SEM photograph taken at a magnification of 3,000× (a bar scale in the photograph represents 1 μm). FIG. 32 is a SEM photograph taken at a magnification of 5,000× (a bar scale in the photograph represents 1 μm). FIG. 33 is a SEM photograph taken at a magnification of 10,000× (a bar scale in the photograph represents 1 μm). In FIGS. 30 to 33, black portions correspond to the C phase and the SiO2 phase, and white portions correspond to the FePt alloy phase. As can be seen from FIGS. 30 to 33, fine regions of the C phase and the SiO2 phase are dispersed in the entire area of the structure.
The average size of the phase consisting of the C phase and the SiO2 phase was determined by the intercept method based on the SEM photograph of FIG. 33 taken at a magnification of 10,000×. A specific method is the same as the method of Reference Example 1. As used herein, the phase consisting of the C phase and the SiO2 phase refers to a phase picked out as the C phase and the SiO2 phase, not distinguishing between the C phase and the SiO2 phase and regarding them as a same phase.
The results showed that the average size of the phase consisting of the C phase and the SiO2 phase determined by the intercept method was 0.20 μm.
Example 5
The targeted composition of a powder mixture and a target in Example 5 is (50Fe-50Pt)-15 vol % C-15 vol % TiO2. That is, the targeted composition of metal components is 50 at % Fe-50 at % Pt; the targeted content of C is 15 vol % based on the total amount of the target; and the targeted content of metal oxide (TiO2) is 15 vol % based on the total amount of the target. When the contents of C and metal oxide (TiO2) are represented not by vol % but by mol %, the targeted composition of the powder mixture and the target in Example 5 is (50Fe-50Pt)-23.04 mol % C-6.39 mol % TiO2.
To 1100.00 g of 50 at % Fe-50 at % Pt alloy powder produced in the same manner as in Reference Example 1, 34.38 g of C powder having an average particle diameter of 35 μm and a bulk density of 0.25 g/cm3 was added so that the content of C is 15 vol % based on the total amount of the powders, and 63.41 g of TiO2 powder having an average particle diameter of 0.07 μm and a bulk density of 4.11 g/cm3 was added so that the content of TiO2 was 15 vol % based on the total amount of the powders. These components were then mixed with a ball mill until the cumulative number of revolutions reached 3,741,120 to produce a powder mixture.
During mixing, the mixing container was hermetically closed with a lid and filled with a gas mixture (Ar+O2); and under the atmosphere in the mixing container, the 50 at % Fe-50 at % Pt alloy powder, the C powder, and the TiO2 powder were mixed.
When the cumulative number of ball mill revolutions reached 935,280, 1,870,560, 2,805,840 and 3,741,120, the mixing container was opened, and whether or not ignition had occurred was visually checked. However, no ignition was found at each point.
When the cumulative number of ball mill revolution reached 1,870,560, 2,805,840 and 3,741,120, 30.00 g of the powder mixture was subjected to hot pressing in a vacuum atmosphere at less than 20 Pa to produce a disc-like sintered product having a diameter of 30 mm. The hot-pressing conditions (sintering temperature, sintering pressure, and sintering time) and the relative density of the obtained sintered product are shown in TABLE 19 below. The theoretical density of the sintered product is 12.45 g/cm3, which is calculated in consideration of a reduction in the amount of carbon during mixing and sintering (i.e., calculated using the content of carbon in the sintered product shown in TABLE 20). Based on this theoretical density, the relative density of the sintered product (sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120) was calculated.










TABLE 19









Relative



Cumulative

density


number of
Hot-pressing conditions
of












ball mill
Sintering
Sintering
Sintering
sintered



revolutions
temperature
pressure
time
product


(Number)
(° C.)
(MPa)
(min)
(%)
Ignition















935,280
—
—
—
—
NO


1,870,560
1350
26.2
45
—
NO


2,805,840
1290
26.2
45
—
NO


3,741,120
1280
26.2
45
95.00
NO









The relative density of the sintered product is 95%, and the amount of voids in the obtained sintered product was small.
The contents of oxygen and nitrogen in the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation, and the content of carbon was measured using a Carbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The contents of oxygen and nitrogen in the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation, and the content of carbon was measured using a Carbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The measurement results are shown in TABLE 20 below.












TABLE 20







Cumulative number






of ball mill



revolutions
Oxygen
Nitrogen
Carbon



of 3,741,120
(mass %)
(mass ppm)
(mass %)





















Powder mixture
4.55
117
2.72



Sintered product
1.88
5
1.86










The content of oxygen and the content of nitrogen in the sintered product both decrease compared to those in the powder mixture, while the degree of reduction in the content of oxygen is smaller than the degree of reduction in the content of nitrogen. This may be caused by the fact that the powder mixture and the sintered product both contain metal oxide TiO2.
As comparing the content of oxygen and the content of nitrogen in the sintered product with those in the powder mixture, the degree of reduction in the content of oxygen and the content of nitrogen due to sintering in Example 5 is larger than that in Reference Examples 1 and 2. This may be because the powder mixture of Example 5 contains the C powder and thus oxygen and nitrogen have been adsorbed to the surface of the C powder.
The structure of the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,741,120 was observed under a scanning electron microscope (SEM). FIGS. 34 to 37 show SEM photographs of the sintered products. FIG. 34 is a SEM photograph taken at a magnification of 1,000× (a bar scale in the photograph represents 10 μm). FIG. 35 is a SEM photograph taken at a magnification of 3,000× (a bar scale in the photograph represents 1 μm). FIG. 36 is a SEM photograph taken at a magnification of 5,000× (a bar scale in the photograph represents 1 μm). FIG. 37 is a SEM photograph taken at a magnification of 10,000× (a bar scale in the photograph represents 1 μm). In FIGS. 34 to 37, black portions correspond to the C phase and the TiO2 phase, and white portions correspond to the FePt alloy phase. As can be seen from FIGS. 34 to 37, fine regions of the C phase and the TiO2 phase are dispersed in the entire area of the structure.
The average size of the phase consisting of the C phase and the SiO2 phase was determined by the intercept method based on the SEM photograph of FIG. 37 taken at a magnification of 10,000×. A specific method is the same as the method of Reference Example 1. As used herein, the phase consisting of the C phase and the TiO2 phase refers to a phase picked out as the C phase and the TiO2 phase, not distinguishing between the C phase and the TiO2 phase and regarding them as a same phase.
The results showed that the average size of the phase consisting of the C phase and the TiO2 phase determined by the intercept method was 0.29 μm.
Reference Example 5
The targeted composition of a powder mixture and a target in Reference Example 5 is (45Fe-45Pt-10Cu)-15 vol % C-15 vol % SiO2. That is, the targeted composition of metal components is 45 at % Fe-45 at % Pt-10 at % Cu; the targeted content of C is 15 vol % based on the total amount of the target; and the targeted content of metal oxide (SiO2) is 15 vol % based on the total amount of the target. When the contents of C and metal oxide (SiO2) are represented not by vol % but by mol %, the targeted composition of the powder mixture and the target in Reference Example 5 is (45Fe-45Pt-10Cu)-24 mol % C-5 mol % SiO2.
The metals in bulk form were weighed such that the composition of the alloy was Fe: 45 at %, Pt: 45 at %, and Cu: 10 at % and then heated by high frequency heating to form a molten Fe—Pt—Cu alloy at 1,800° C. Then a gas atomizing method using argon gas was performed to produce 45 at % Fe-45 at % Pt-10 at % Cu alloy powder. The average particle diameter of the obtained alloy powder was measured using Microtrac MT3000 manufactured by NIKKISO Co., Ltd. and found to be 50 μm.
To 1020.00 g of the obtained 45 at % Fe-45 at % Pt-10 at % Cu alloy powder, 44.63 g of C powder having an average particle diameter of 35 μm and a bulk density of 0.25 g/cm3 was added so that the content of C is 15 vol % based on the total amount of the powders, and 32.56 g of SiO2 powder having an average particle diameter of 0.7 μm and a bulk density of 2.20 g/cm3 was added so that the content of SiO2 was 15 vol % based on the total amount of the powders. These components were then mixed with a ball mill until the cumulative number of revolutions reached 5,736,960 to produce a powder mixture.
During mixing, the mixing container was hermetically closed with a lid and filled with a gas mixture (Ar+O2); and under the atmosphere in the mixing container, the 45 at % Fe-45 at % Pt-10 at % Cu alloy powder, the C powder, and the SiO2 powder were mixed.
When the cumulative number of ball mill revolutions reached 935,280, 2,535,840, 4,136,400 and 5,736,960, the mixing container was opened, and whether or not ignition had occurred was visually checked. However, no ignition was found at each point.
When the cumulative number of ball mill revolution reached 5,736,960, 30.00 g of the powder mixture was subjected to hot pressing in a vacuum atmosphere at less than 20 Pa to produce a disc-like sintered product having a diameter of 30 mm. The hot-pressing conditions (sintering temperature, sintering pressure, and sintering time) and the relative density of the obtained sintered product are shown in TABLE 21 below. The theoretical density of the sintered product is 11.11 g/cm3, which is calculated in consideration of a reduction in the amount of carbon during mixing and sintering (i.e., calculated using the content of carbon in the sintered product shown in TABLE 22). Based on this theoretical density, the relative density of the sintered product (sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 5,736,960) was calculated.










TABLE 21









Relative



Cumulative

density


number of
Hot-pressing conditions
of












ball mill
Sintering
Sintering
Sintering
sintered



revolutions
temperature
pressure
time
product


(Number)
(° C.)
(MPa)
(min)
(%)
Ignition















935,280
—
—
—
—
NO


2,535,840
—
—
—
—
NO


4,136,400
—
—
—
—
NO


5,736,960
1420
24.5
45
93.36
NO









The relative density of the sintered product exceeds 93%, and the amount of voids in the obtained sintered product was small.
The contents of oxygen and nitrogen in the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 5,736,960 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation, and the content of carbon was measured using a Carbon/Sulfur Analyzer manufactured by HORIBA, Ltd. The measurement results are shown in TABLE 22 below.












TABLE 22







Cumulative number






of ball mill



revolutions
Oxygen
Nitrogen
Carbon



of 5,736,960
(mass %)
(mass ppm)
(mass %)









Sintered product
1.46
23
3.30










The structure of the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 5,736,960 was observed under a scanning electron microscope (SEM). FIGS. 38 to 40 show SEM photographs of the sintered products. FIG. 38 is a SEM photograph taken at a magnification of 3,000× (a bar scale in the photograph represents 1 μm). FIG. 39 is a SEM photograph taken at a magnification of 5,000× (a bar scale in the photograph represents 1 μm). FIG. 40 is a SEM photograph taken at a magnification of 10,000× (a bar scale in the photograph represents 1 μm). In FIGS. 38 to 40, black portions correspond to the C phase and the TiO2 phase, and white portions correspond to the FePtCu alloy phase. As can be seen from FIGS. 38 to 40, fine regions of the C phase and the SiO2 phase are dispersed in the entire area of the structure.
The average size of the phase consisting of the C phase and the SiO2 phase was determined by the intercept method based on the SEM photograph of FIG. 40 taken at a magnification of 10,000×. A specific method is the same as the method of Reference Example 1. As used herein, the phase consisting of the C phase and the SiO2 phase refers to a phase picked out as the C phase and the SiO2 phase, not distinguishing between the C phase and the SiO2 phase and regarding them as a same phase.
The results showed that the average size of the phase consisting of the C phase and the SiO2 phase determined by the intercept method was 0.27 μm.
Reference Example 6
The targeted composition of a powder mixture and a target in Reference Example 6 is (50Fe-45Pt-5Cu)-20.3 vol % B2O3. That is, the targeted composition of metal components is 50 at % Fe-45 at % Pt-5 at % Cu; and the targeted content of metal oxide (B2O3) is 20.3 vol % based on the total amount of the target. When the content of metal oxide (B2O3) is represented not by vol % but by mol %, the targeted composition of the powder mixture and the target in Reference Example 6 is (50Fe-45Pt-5Cu)-5.11 mol % B2O3.
The metals in bulk form were weighed such that the composition of the alloy was Fe: 50 at %, Pt: 45 at %, and Pt: 5 at % and then heated by high frequency heating to form a molten Fe—Pt—Cu alloy at 1,800° C. Then a gas atomizing method using argon gas was performed to produce 50 at % Fe-45 at % Pt-5 at % Cu alloy powder. The average particle diameter of the obtained alloy powder was measured using Microtrac MT3000 manufactured by NIKKISO Co., Ltd. and found to be 50 μm.
To 1030.00 g of the obtained 50 at % Fe-45 at % Pt-5 at % Cu alloy powder, 32.49 g of B2O3 powder was added so that the content of B2O3 is 20.3 vol % based on the total amount of the powders. These components were then mixed with a ball mill until the cumulative number of revolutions reached 3,852,360 to produce a powder mixture.
During mixing, the mixing container was hermetically closed with a lid and filled with a gas mixture (Ar+O2); and under the atmosphere in the mixing container, the 50 at % Fe-45 at % Pt-5 at % Cu alloy powder and the B2O3 powder were mixed.
When the cumulative number of ball mill revolutions reached 1,046,520, 1,981,800, 2,917,080 and 3,852,360, the mixing container was opened, and whether or not ignition had occurred was visually checked. However, no ignition was found at each point.
When the cumulative number of ball mill revolution reached 3,852,360, 30.00 g of the powder mixture was subjected to hot pressing in a vacuum atmosphere at less than 20 Pa to produce a disc-like sintered product having a diameter of 30 mm. The hot-pressing conditions (sintering temperature, sintering pressure, and sintering time) and the relative density of the obtained sintered product are shown in TABLE 23 below. As shown below in TABLE 25, the content of B increased only by 0.04% by mass compared to the state of the powder mixture before sintering in the ICP analysis results. Since there was no step involving direct incorporation of B2O3 in a series of steps including ICP analysis, the theoretical density of the sintered product was calculated without consideration of an increase in the content of B and found to be 12.22 g/cm3. The relative density of the sintered product (sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,852,360) was calculated based on the theoretical density of 12.22 g/cm3 and found to be 100.09%.










TABLE 23









Relative



Cumulative

density


number of
Hot-pressing conditions
of












ball mill
Sintering
Sintering
Sintering
sintered



revolutions
temperature
pressure
time
product


(Number)
(° C.)
(MPa)
(min)
(%)
Ignition





1,046,520
—
—
—
—
NO


1,981,800
—
—
—
—
NO


2,917,080
—
—
—
—
NO


3,852,360
770
26.2
45
100.09
NO









The relative density of the sintered product exceeds 100%, and the amount of voids in the obtained sintered product was small.
The contents of oxygen and nitrogen in the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,852,360 were measured using a TC-600 Series Nitrogen/Oxygen Determinator manufactured by LECO Corporation. The measurement results are shown in TABLE 24 below.











TABLE 24







Cumulative number





of ball mill



revolutions
Oxygen
Nitrogen



of 3,852,360
(mass %)
(mass ppm)









Sintered product
2.70
58










The contents of Fe, Pt, Cu, and B in the sintered product made of the powder mixture taken at a cumulative number of ball mill revolutions of 3,852,360 were analyzed by ICP. TABLE 25 below shows the analysis results as well as the contents of Fe, Pt, Cu, and B in the powder mixture before sintering. The contents of Fe, Pt, Cu, and B in the powder mixture before sintering are not the analysis results by ICP but the calculated values (theoretical values) based on the amounts of raw material powders blended for producing the powder mixture.











TABLE 25





Cumulative






number of ball


mill revolutions
Fe
Pt
Cu
B


of 3,852,360
(mass %)
(mass %)
(mass %)
(mass %)







Powder mixture
22.77
71.58
2.59
0.95


Sintered product
22.95
72.73
2.38
0.99









The structure of the sintered product made using the powder mixture taken at a cumulative number of ball mill revolutions of 3,852,360 was observed under a scanning electron microscope (SEM). FIGS. 41 to 44 show SEM photographs of the sintered products. FIG. 41 is a SEM photograph taken at a magnification of 1,000× (a bar scale in the photograph represents 10 μm). FIG. 42 is a SEM photograph taken at a magnification of 3,000× (a bar scale in the photograph represents 1 μm). FIG. 43 is a SEM photograph taken at a magnification of 5,000× (a bar scale in the photograph represents 1 μm). FIG. 44 is a SEM photograph taken at a magnification of 10,000× (a bar scale in the photograph represents 1 μm). In FIGS. 41 to 44, black portions correspond to the B2O3 phase, and white portions correspond to the FePtCu alloy phase. As can be seen from FIGS. 41 to 44, fine regions of the B2O3 phase are dispersed in the entire area of the structure.
The average size of the B2O3 phase was determined by the intercept method based on the SEM photograph of FIG. 44 taken at a magnification of 10,000×. A specific method is the same as the method of Reference Example 1.
The results showed that the average size of the B2O3 phase determined by the intercept method was 0.14 μm.
Comparative Example 1
The targeted composition of a powder mixture and a target in Comparative example 1 is (50Fe-50Pt)-30 vol % C. More specifically, the targeted composition of the metal components is 50 at % Fe-50 at % Pt, and the targeted content of C is 30 vol % based on the total amount of the target. When the content of C is represented not by vol % but by at %, the targeted composition of the powder mixture and the target in Comparative example 1 is (50Fe-50Pt)-40 at % C.
A powder mixture and a sintered product were produced in the same manner as in Example 1 except that C powder was used instead of SiO2 powder, that a mixing container was filled with argon (Ar) and hermetically sealed, and FePt powder and C powder were mixed in the sealed mixing container, that the cumulative number of ball mill revolutions was changed, that the number of times and the timing of introduction of fresh air by opening the mixing container during mixing were changed, and that the sintering temperature during the production of the sintered product was changed to 1,100° C.
When the cumulative number of ball mill revolutions reached 209,520, 608,040, 1,006,560, 1,405,080, 1,803,600, 2,202,120, and 2,816,640, the mixing container was opened, and whether or not ignition had occurred was visually checked. Until the point of time when the cumulative number of ball mill revolutions was 2,202,120, no ignition was found. However, at the point of time when the cumulative number of ball mill revolutions was 2,816,640, ignition was found.
To be precise, the atmosphere in the mixing container during mixing was the sealed gas mixture (Ar—O2) atmosphere only in the initial stage of mixing (until the cumulative number of ball mill revolutions reached 209,520) and was a sealed argon (Ar) atmosphere thereafter. The mixing was performed in the sealed gas mixture (Ar—O2) atmosphere only in the initial stage of mixing (until the cumulative number of ball mill revolutions reached 209,520). This cumulative number of ball mill revolutions is only 7.4% of the final cumulative number of ball mill revolutions, i.e., 2,816,640, so that the amount of oxygen adsorbed on the surface of the C powder in the initial stage of mixing (until the cumulative number of ball mill revolutions reached 209,520) is considered to be small. Therefore, Comparative Example 1 is thought to be an experimental example in which the FePt powder and the C particles having a certain amount or less of oxygen adsorbed thereon are mixed 2,816,640−209,520=2,607,120 times in the argon (Ar) atmosphere.
30.00 g of the powder mixture mixed until the cumulative number of ball mill revolutions reached 1,405,080 was subjected to hot pressing under the conditions of temperature: 1,100° C., pressure: 25 MPa, time: 45 min., atmosphere: a vacuum of 5×10−2 Pa or lower to thereby produce a disc-like sintered product having a diameter of 30 mm.
The density of each of the produced sintered products was measured by the Archimedes method, and the measured value was divided by a theoretical density to determine the relative density. The results are shown in TABLE 26 below. In Comparative Example 1, the theoretical density was not computed in consideration of a reduction in the amount of carbon during sintering, as was in Examples 5 to 10.











TABLE 26






Sintering

Theoretical
Relative


Sintered powder
temperature
Density
density
density


mixture
(° C.)
(g/cm3)
(g/cm3)
(%)







Powder mixture
1,100
8.16
11.47
71.1


when cumulative


number of ball


mill revolutions


was 1,810,080









The relative density of the sintered product was low, i.e., 71.1%, so that the sintered product contained a large amount of voids. If the relative density is computed using the theoretical density computed in consideration of a reduction in the amount of carbon during sintering, the relative density in Comparative Example 1 may be much smaller than 71.1%.
(Discussion)
The principal experimental data in Examples 1 to 5 and Reference Examples 1 to 6, and Comparative Example 1 is summarized in TABLE 27 below. In TABLE 27, the average size of the phase means the average size of the metal oxide phase in Reference Examples 1 to 4 and 6, or means the average size of the phase consisting of the C phase and the metal oxide phase in Examples 1 to 5 and Reference Example 5.















TABLE 27









Cumulative









number of


Average




Atmosphere
ball mill
Sintering
Relative
size of




during
revolutions
temperature
density
phase
Igni-



Composition of target
mixing
(Number)
(° C.)
(%)
(μm)
tion























Reference
(50Fe—50Pt)—30 vol % SiO2
Ar + O2
3,741,120
1050
98.61
0.34
NO


example 1


Reference
(50Fe—50Pt)—30 vol % TiO2
Ar + O2
3,741,120
950
96.69
0.28
NO


example 2


Reference
(50Fe—50Pt)—36.63 vol % B2O3
Ar + O2
5,736,960
840
105.22
0.22
NO


example 3


Reference
(50Fe—50Pt)—12.07 vol % B2O3—24.68 vol % SiO2
Ar + O2
3,852,360
830
100.38
0.27
NO


example 4


Example 1
(50Fe—50Pt)—6 vol % C—24 vol % SiO2
Ar + O2
3,741,120
1270
97.31
0.28
NO


Example 2
(50Fe—50Pt)—9 vol % C—21 vol % SiO2
Ar + O2
3,741,120
1280
97.50
0.23
NO


Example 3
(50Fe—50Pt)—12 vol % C—18 vol % SiO2
Ar + O2
3,741,120
1300
96.68
0.3
NO


Example 4
(50Fe—50Pt)—15 vol % C—15 vol % SiO2
Ar + O2
3,741,120
1290
95.81
0.2
NO


Example 5
(50Fe—50Pt)—15 vol % C—15 vol % TiO2
Ar + O2
3,741,120
1280
95.00
0.29
NO


Reference
(45Fe—45Pt—10Cu)—15 vol % C—15 vol % SiO2
Ar + O2
5,736,960
1420
93.36
0.27
NO


example 5


Reference
(50Fe—45Pt—5Cu)—20.3 vol % B2O3
Ar + O2
3,852,360
770
100.09
0.14
NO


example 6


Comparative
(50Fe—50Pt)—30 vol % C
Ar
1,405,080
1100
71.10
—
NO


example 1


2,816,640
—
—
—
Yes









In Examples 1 to 5 and Reference Examples 1 to 6, no ignition was found even after the cumulative number of ball mill revolutions reached 3,000,000.
In Examples 1 to 5 and Reference Examples 1 to 4, Fe is alloyed with Pt to form FePt alloy powder; in Reference Examples 5 and 6, Fe is alloyed with Pt and Cu to form FePtCu alloy powder. This can reduce the activity of Fe even in the form of powder, thereby suppressing oxidation and ignition of Fe during mixing with the metal oxide powder or during mixing with the metal oxide powder and the C powder.
In Examples 1 to 5 and Reference Example 5, the powder mixture contains C powder. Since the atmosphere during the production of the powder mixture is a gas mixture (Ar+O2), i.e., the atmosphere contains oxygen, a certain amount of oxygen is adsorbed to the surface of the C powder during mixing. Therefore, a certain amount of oxygen has already been adsorbed to the surface of C particles, and accordingly rapid adsorption of oxygen to the surface of the C particles and subsequent ignition of the C particles hardly occur even when the mixing container is opened to introduce the air after mixing, thereby allowing stable production even of the FePt-based sputtering target containing not only the metal oxide but also C.
However, in Reference Example 1 in which the FePt powder and the C powder were mixed in an argon atmosphere containing no oxygen during a period from when the cumulative number of ball mill revolutions was 209,521 to when it reached 2,816,640, ignition was found when the mixing container was opened at the point of time when the cumulative number of ball mill revolutions was 2,816,640. In Reference Example 1, this may be caused by mixing of the FePt powder and the C powder in an argon atmosphere containing no oxygen during a period from when the cumulative number of ball mill revolutions was 209,521 to when it reached 2,816,640, and by the content of the C powder as large as 30 vol %.
In Examples 1 to 5 and Reference Examples 1 to 6, the cumulative number of ball mill revolutions was 3,000,000 or more, i.e., in Examples 1 to 5 and Reference Examples 1 to 6, the powder mixtures were produced by sufficient mixing. Therefore, in Examples 1 to 5 and Reference Examples 1 to 6, the metal oxide powder and the C powder in the powder mixtures became small enough. Accordingly, this may allow, in the sintered products produced in Examples 1 to 5 and Reference Examples 1 to 6, the size of the metal oxide phase, or the average size of the phase consisting of the C phase and the SiO2 phase, as measured by the intercept method, to be as small as 0.14 to 0.34 μm. Also this may allow the obtained sintered products to have a relative density as large as 90% or more.
In Comparative Example 1, the sintered product was produced using the powder mixture mixed until the cumulative number of ball mill revolutions reached 1,405,080, but the relative density of the produced sintered product was as small as 71.1%. One reason for this may be the influence of low sintering temperature, 1,100° C., in Reference Example 1. Another reason may be that, since the cumulative number of ball mill revolutions was small, the particle diameter of the C powder in the powder mixture used to produce the sintered product was not sufficiently reduced, so that voids in the sintered product became large and the relative density of the sintered product became small.
INDUSTRIAL APPLICABILITY
The target according to the present invention can be preferably used as an FePt-based sputtering target. The production process according to the present invention can be preferably used as a process for producing an FePt-based sputtering target.
REFERENCE SIGNS LIST


    
    
        10 Substrate
        10A Substrate surface
        12 FePt alloy particles
        14 Carbon phase

## Claims

1. An FePt-based sputtering target comprising Fe, Pt, C, and a metal oxide,
wherein the FePt-based sputtering target has a structure in which an FePt-based alloy phase, a C phase containing unavoidable impurities, and a metal oxide phase containing unavoidable impurities are mutually dispersed, the FePt-based alloy phase containing Pt in an amount of 40 at % or more and 60 at % or less with the balance being Fe and unavoidable impurities, and
wherein C is contained in an amount of more than 0 vol % and 20 vol % or less based on a total amount of the target, the metal oxide is contained in an amount of 10 vol % or more and less than 40 vol % based on the total amount of the target, and a total content of C and the metal oxide is 20 vol % or more and 40 vol % or less based on the total amount of the target.

2. The FePt-based sputtering target according to claim 1,
wherein a phase consisting of the C phase and the metal oxide phase has an average size of 0.4 μm or less as determined by an intercept method.

3. The FePt-based sputtering target according to claim 1,
wherein the metal oxide contains at least one of SiO2, TiO2, Ti2O3, Ta2O5, Cr2O3, CoO, Co3O4, B2O3, Fe2O3, CuO, Cu2O, Y2O3, MgO, Al2O3, ZrO2, Nb2O5, MoO3, CeO2, Sm2O3, Gd2O3, WO2, WO3, HfO2, and NiO2.

4. The FePt-based sputtering target according to claim 2,
wherein the metal oxide contains at least one of SiO2, TiO2, Ti2O3, Ta2O5, Cr2O3, CoO, Co3O4, B2O3, Fe2O3, CuO, Cu2O, Y2O3, MgO, Al2O3, ZrO2, Nb2O5, MoO3, CeO2, Sm2O3, Gd2O3, WO2, WO3, HfO2, and NiO2.

5. The FePt-based sputtering target according to claim 1,
wherein the FePt-based sputtering target has a relative density of 90% or higher.

6. The FePt-based sputtering target according to claim 2,
wherein the FePt-based sputtering target has a relative density of 90% or higher.

7. The FePt-based sputtering target according to claim 1,
wherein the FePt-based sputtering target is used for a magnetic recording medium.

8. The FePt-based sputtering target according to claim 2,
wherein the FePt-based sputtering target is used for a magnetic recording medium.