Metal treatment – Stock – Containing over 50 per cent metal – but no base metal
Reexamination Certificate
1998-07-28
2001-08-07
Sheehan, John (Department: 1773)
Metal treatment
Stock
Containing over 50 per cent metal, but no base metal
C148S314000, C148S315000, C148S423000, C148S424000, C148S425000, C148S430000, C420S072000, C420S428000, C420S434000, C420S435000, C420S461000, C420S466000, C420S580000, C420S581000
Reexamination Certificate
active
06270593
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to Mn alloy materials for magnetic materials, Mn alloy sputtering targets, and magnetic thin films. More particularly, this invention relates to Mn alloys for anti-ferromagnetic thin films, Mn alloy sputtering targets, and anti-ferromagnetic thin films.
Magnetic recording media for computers, such as hard disks, have in recent years been rapidly reduced in size but expanded in capacity; recording densities as high as 200 Gb/in
2
are expected to be realized in years to come. Accordingly, recording heads of the conventional induction type have approached the limit of their utility and are being supplanted by magnetoresistance effect type (AMR) heads. The spread of the personal computer market promises dramatic growth of demand for the AMR heads on the global basis. In a few years the heads of giant magnetoresistance effect type (GMR) with even greater density potential will come in practical use.
GMR heads use a spin valve film of antimagnetic film, and Mn alloys have been studied as possible materials for forming the antimagnetic film.
Mn alloys, especially Mn-Fe alloys and the like, are investigated for the particular application. However, the use of Mn—Fe alloys in fact has a rather unlikely prospect because of their questionable corrosion resistance. Attempts have been made to improve the corrosion resistance by adding noble metals to Mn. The problems they present are that the noble metals are expensive and even the addition of such metals has not enhanced the resistance to a fully satisfactory level.
OBJECT OF THE INVENTION
This invention aims at providing means for forming excellently corrosion-resistant, antimagnetic films.
SUMMARY OF THE INVENTION
With the view of settling the problems of the prior art, the present inventors have made intensive research. As a result, it has now been found that impurity elements, especially oxygen and sulfur, in Mn alloys deteriorate the corrosion resistance.
This invention, on the basis of the above finding, provides:
1. an Mn alloy material for magnetic materials characterized in that it contains 500 ppm or less oxygen and 100 ppm or less sulfur,
2. an Mn alloy material for magnetic materials characterized in that it contains a total of 1000 ppm or less impurities (other than Mn and the alloying component), wherein it contains 500 ppm or less oxygen and 100 ppm or less sulfur,
3. an Mn alloy material for magnetic materials characterized in that it contains a total of 500 ppm or less impurities (other than Mn and the alloying component), wherein 100 ppm or less oxygen, and 20 ppm or less sulfur, and
4. an alloy material according to 1, 2, or 3 above characterized in that the alloying component that constitutes the alloy with Mn is one or two or more elements selected from the group consisting of Fe, Ir, Pt, Pd, Rh, Ru, Ni, Cr, and Co.
This invention also provides:
5. a Mn alloy sputtering target for forming a magnetic thin film characterized in that it contains 500 ppm or less oxygen and 100 ppm or less sulfur,
6. a Mn alloy sputtering target for forming a magnetic thin film characterized in that it contains a total of 1000 ppm or less impurities (other than Mn and the alloying component), wherein it contains 500 ppm or less oxygen and 100 ppm or less sulfur,
7. a Mn alloy sputtering target for forming a magnetic thin film characterized in that it contains a total of 500 ppm or less impurities (other than M n and the alloying component), wherein it contains 100 ppm or less oxygen and 20 ppm or less sulfur.
8. a sputtering target according to 5, 6, or 7 above characterized in that the alloying component that constitutes the alloy with Mn is one or two or more elements selected from the group consisting of Fe, Ir, Pt, Pd, Rh, Ru, Ni, Cr, and Co.
This invention further provides:
9. a magnetic thin film characterized in that it is formed by sputtering with an Mn alloy sputtering target for forming magnetic thin film according to any of 5 to 8 above.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An Mn alloy material for magnetic materials according to this invention consists of an alloy containing Mn as its main constituent. Alloying components other than Mn include Fe, Ir, Pt, Pd, Rh, Ru, Ni, Cr, and Co. In particular, alloys of Mn—Fe, Mn—Ir, and Mn—Rh—Ru systems are useful for forming antimagnetic films. For example, these alloys have the following compositional ranges:
Mn—Fe alloy: 30-70 wt % Mn—70-30 wt % Fe,
Mn—Ni alloy: 60-90 wt % Mn—40-10 wt % Ni,
Mn—Pt alloy: 10-40 wt % Mn—90-60 wt % Pt,
Mn—Ir alloy: 30-70 wt % Mn—70-30 wt % Ir,
Mn—Pd—Pt alloy: 15-45 wt % Mn—15-45 wt % Pd—25-55 wt % Pt,
Mn—Rh—Ru alloy: 60-80 wt % Mn—15-35 wt % Rh—0-15 wt % Ru,
Mn—Co alloy: 30-70 wt % Mn—70-30 wt % Co,
Mn—Cr alloy: 30-70 wt % Mn—70-30 wt % Cr.
The alloy material according to this invention has lower oxygen and sulfur contents than usual. Oxygen and sulfur are major elements that deteriorate the corrosion resistance of the alloy. The oxygen content should be reduced to 500 ppm or less, preferably 100 ppm or less, and the sulfur content to 100 ppm or less, preferably 20 ppm or less.
Also desirable is the reduction of the impurity level; the total content of the elements other than Mn and the alloying component is reduced to 1000 ppm or below. The impurities or elements other than Mn and the alloying component deteriorate the magnetic characteristics and can lower the corrosion resistance of the resulting alloy. Therefore, the impurity content should be minimized to a total amount of 1000 ppm or less, preferably 500 ppm or less. A total impurity content of more than 1000 ppm is undesirable because it seriously aggravates the magnetic characteristics and corrosion resistance.
The Mn alloy material thus reduced in the impurity content can be produced in the following way.
In view of the fact that the impurities, especially oxygen and sulfur, in the Mn alloy are derived from the electrolytic Mn as the starting material, the inventors purified the material Mn to a higher purity than before.
Commercially available electrolytic Mn was subjected to high frequency melting with the addition of Ca, Mg, La, etc. as deoxidizers to remove oxygen and sulfur. The melting is preferably carried out in an inert gas atmosphere under reduced pressure, since it satisfactorily reduces the levels of impurity elements other than oxygen and sulfur too.
As an alternative method for highly purifying Mn, it is possible to premelt electrolytic Mn and then subject the melt to vacuum distillation, whereby the impurity level is lowered.
The alloying component other than Mn should also be as high in purity as possible. When they are procured from the market, highly pure products with a purity of at least 99.9% each should be used. Where necessary, they are freed from gaseous impurities and the like, e.g., by vacuum degassing.
The Mn and alloying components other than Mn thus obtained are melted together for alloying and the melt is cast. The alloy ingot so obtained is machined to a sputtering target material. Basically the purity of the target is equal to that of the ingot.
The sputtering target obtained this way is used in sputtering to deposit a magnetic thin film.
REFERENCES:
patent: 2259459 (1941-10-01), Dean
patent: 2329698 (1943-09-01), Dean
patent: 4282032 (1981-08-01), Nagoya et al.
patent: 4354868 (1982-10-01), Demange et al.
patent: 4415529 (1983-11-01), Masumoto et al.
Shindo Yuichiro
Suzuki Tsuneo
Akin Gump Strauss Hauer & Feld L.L.P.
Japan Energy Corporation
Sheehan John
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