Claims
- 1. A process for preparing ferromagnetic metalinsulator composites having a metal volume fraction within the range of from about 0.30 to about 0.55 and a metal particle size within the range of from about 30 .ANG. to about 200 .ANG. comprising the steps:
- a. Preparing a composite target comprising a mixture of a ferromagnetic metal and an insulator;
- b. Placing said composite target in a sputtering apparatus containing an inert sputtering gas and a substrate;
- c. Maintaining the substrate at a temperature within the range of from about 700.degree. K. to about 800 .degree. K., and
- d. Subjecting said composite target to ionic bombardment to thereby sputter a homogeneous film of said ferromagnetic metal and said insulator onto the surface of said substrate.
- 2. The process of claim 1 wherein said ferromagnetic metal is selected from the group consisting of Fe, Co, Ni and alloys thereof, and said insulator is selected from the group consisting of SiO.sub.2 and Al.sub.2 O.sub.3.
- 3. The process of claim 2 wherein said composite target is a homogeneous mixture of said ferromagnetic metal and said insulator and said sputtering apparatus is a magnetron.
- 4. The process of claim 3 wherein said inert sputtering gas is argon at a pressure of about 2 to about 3 .mu. of mercury.
- 5. The process of claim 4 wherein said ferromagnetic metal is Fe and said insulator is SiO.sub.2.
- 6. The process of claim 5 wherein the volume fraction of Fe is about 0.42 and the particle size of Fe is about 150 .ANG..
- 7. The process of claim 6 wherein said substrate is at a temperature of about 775.degree. K.
- 8. The process of claim 7 wherein the deposition rate of the composite of Fe and SiO.sub.2 onto said substrate is about 0.05 .mu./min.
- 9. The process of claim 4 wherein said ferromagnetic metal is Co having a particle size of about 150 .ANG..
- 10. The process of claim 4 wherein said ferromagnetic metal is Ni having a particle size of about 150 .ANG..
- 11. Ferromagnetic metal-insulator composites having a metal volume fraction within the range of from about 0.30 to about 0.55 and a metal particle size within the range of from about 30 .ANG. to about 200 .ANG. prepared by a process comprising the steps:
- a. Preparing a composite target comprising a mixture of a ferromagnetic metal and an insulator;
- b. Placing said composite target in a sputtering apparatus containing an inert sputtering gas and a substrate;
- c. Maintaining the substrate at a temperature within the range of from about 700.degree. K. to about 800.degree. K., and
- d. Subjecting said composite target to ionic bombardment to thereby sputter a homogeneous film of said ferromagnetic metal and said insulator onto the surface of said substrate.
- 12. The ferromagnetic metal-insulator composites of claim 11 wherein said ferromagnetic metal is selected from the group consisting of Fe, Co, Ni and alloys thereof, and said insulator is selected from the group consisting of SiO.sub.2 and Al.sub.2 O.sub.3.
- 13. The ferromagnetic metal-insulator composites of claim 12 wherein said composite target is a homogeneous mixture of said ferromagnetic metal and said insulator and said sputtering apparatus is a magnetron.
- 14. The ferromagnetic metal-insulator composites of claim 13 wherein said inert sputtering gas is argon at a pressure of about 2 to about 3 .mu. of mercury.
- 15. The ferromagnetic metal-insulator composites of claim 14 wherein said ferromagnetic metal is Fe and said insulator is SiO.sub.2.
- 16. The ferromagnetic metal-insulator composites of claim 15 wherein the volume fraction of Fe is about 0.42 and the particle size of Fe is about 150 .ANG..
- 17. The ferromagnetic metal-insulator composites of claim 16 wherein said substrate is at a temperature of about 75.degree. K.
- 18. The ferromagnetic metal-insulator composites of claim 17 wherein the deposition rate of the composite of Fe and SiO.sub.2 unto said substrate is about 0.05 .mu./min.
- 19. The ferromagnetic metal-insulator composites of claim 14 wherein said ferromagnetic metal is Co having a particle size of about 150 .ANG..
- 20. The ferromagnetic metal-insulator composites of claim 14 wherein said ferromagnetic metal is Ni having a particle size of about 150 .ANG..
BACKGROUND OF THE INVENTION
This invention was made with Government support under Contract N0014-85-K-0175 awarded by the Department of the Navy. The Government has certain rights in the invention.
The invention described and claimed herein was made under a contract from the Office of Naval Research.
This invention is broadly concerned with metalinsulator composites having improved properties, and their method of preparation. More particularly, it is concerned with ferromagnetic metal-ceramic composites, i.e., cermets, having properties that make them particularly useful as high density recording media. By carefully controlling process conditions, cermets having high magnetization and high coercivity as well as chemical stability, wear resistance and corrosion resistance are prepared.
The demand for high density recording media with superior magnetic properties is constantly increasing. Such recording media must also be chemically stable and wear resistant. Magnetic granular solids in which ultrafine magnetic particles are imbedded in an insulating matrix offer attractive features as recording media. The insulating matrix greatly enhances the chemical stability of the ultrafine magnetic particles as well as the wear and corrosion resistance of the media. In addition, since vapor deposition is the most effective method of making granular metal films, the fabrication, dispersion and protection of the ultrafine granules, as well as coating onto desired surfaces suitable for device applications, are achieved in a single process.
In granular metal films, the microstructure is crucial to the magnetic properties. The magnetic properties of the granular solids are microstructure-controlled and can be tailored through careful control of the process conditions for their preparation. The size and shape of the metal granules, their connectivity and associated percolation behavior, and their volume fraction in the composite are of primary importance. We show in our paper in Appl. Phys. Lett., 51, 1280 (1987) that in granular Fe-Si02, when the metal volume fraction (p) is near but below the percolation threshold (p.sub.c), greatly enhanced magnetic properties are realized. The coercivity (H.sub.c) at low temperature was found to be as high as two orders of magnitude greater than that of bulk iron. However, the metal granules were relatively small, i.e., smaller than about 70 .ANG.. Consequently, coercivity at room temperature was greatly reduced, primarily due to superparamagnetic relaxation. The paper by Chien et al. in J. of Magnetism and Magnetic Materials, 54-57, 759-760 (1986) is a preliminary study which describes Fe-SiO.sub.2 composites having an iron volume fraction of 0.52 and estimated average iron granule sizes of about 90 .ANG. and about 160 .ANG.. However, these composites are deficient as high density recording media in that their levels of magnetization and coercivity at room temperature are not sufficiently high. This is a result of the method by which they were prepared.
Broadly, this invention is concerned with a process for preparing improved ferromagnetic metal-insulator composites, i.e., cermets, and the cermets produced by said process. More particularly, the invention is concerned with cermets and a process for their preparation wherein said cermets have superior properties such as high magnetization and surprisingly high coercivity as well as chemical stability, wear resistance and corrosion resistance. Such cermets find particular utility as high density recording media. It has been found that there is a relationship between the magnetic properties of the cermets and their microstructure. By carefully controlling process conditions, the microstructure, and hence the magnetic properties, of the cermets can be controlled. The cermets of this invention are made by a sputtering process using a radio frequency (rf) source, a simple direct current (dc) source or a magnetron. The process variables that have the most pronounced effect on the magnetic properties of the cermet are the inert sputtering gas pressure, deposition rate and substrate temperature. The metal volume fraction and the metal particle size in the resultant cermet are also critical factors.
It is therefore an object of this invention to provide metal-insulator composites having improved properties as well as a novel process for their preparation.
It is another object of this invention to provide ferromagnetic metal-ceramic composites having improved magnetic properties as well as a novel process for their preparation.
It is yet another object of this invention to provide ferromagnetic metal-ceramic composites having high magnetization and high coercivity as well as chemical stability, wear resistance and corrosion resistance.
It is still another object of this invention to provide a process for the preparation of ferromagnetic metal-ceramic composites having high magnetization and high coercivity as well as chemical stability, wear resistance and corrosion resistance.
Yet other objects will be apparent to those skilled in the art. The foregoing and other objects are accomplished by the practice of this invention. Broadly, viewed in one of its principal aspects, this invention consists of a process for preparing ferromagnetic metal-insulator composites having a metal volume fraction within the range of from about 0.30 to about 0.55 and a metal particle size within the range of from about 30 .ANG. to about 200 .ANG. comprising the steps:
1. Preparing a composite target comprising a mixture of a pure ferromagnetic metal and an insulator;
2. Placing said composite target in a sputtering apparatus containing a substrate;
3. Maintaining the substrate at a temperature within the range of from about 300.degree. K. to about 900.degree. K., and
4. Subjecting said composite target to ionic bombardment to thereby sputter a homogeneous film of said ferromagnetic metal and said insulator onto the surface of said substrate.
The cermets of this invention are ferromagnetic metal-insulator composites having a metal volume fraction with the range of from about 0.30 to about 0.55 and a metal particle size within the range of from about 30 .ANG. to about 200 .ANG. prepared by a process comprising the steps:
1. Preparing a composite target comprising a mixture of a pure ferromagnetic metal and an insulator;
2. Placing said composite target in a sputtering apparatus containing a substrate;
3. Maintaining the substrate at a temperature within the range of from about 300.degree. K. to about 900.degree. K., and
4. Subjecting said composite target to ionic bombardment to thereby sputter a homogeneous film of said ferromagnetic metal and said insulator onto the surface of said substrate.
The instant invention thus provides metal-insulator composites, i.e., cermets, having improved properties, and their method of preparation. More particularly, this invention provides ferromagnetic metal-ceramic composites having properties that make them particularly useful a high density recording media. It has been found that there is a relationship between the magnetic properties of the cermets and their microstructure. By carefully controlling the process conditions for their preparation, the microstructure, and hence the magnetic properties, of the cermets can be controlled. The cermets of this invention are made by a sputtering process using a radio frequency (rf) source, a simple direct current (dc) source or a magnetron. The process variables that have the most pronounced effect on the magnetic properties of the cermets are the inert sputtering gas pressure, deposition rate, and substrate temperature. Other critical parameters are the metal particle size and the metal volume fraction in the resultant cermet.
The nature and substance of the present invention as well as it objects and advantages will be more clearly perceived and fully understood by referring to the following description and claims taken in connection with the accompanying drawings which are described briefly below.
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Non-Patent Literature Citations (4)
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| Chien et al., "Granular Fe Metal Films", J. of Mag. and Mag. Materials, 54-57 (1986). |
| Liou et al., "Granular . . . Media", Appl. Phys. Lett., 52(6), Feb. 8, 1988. |
| Xiao et al., "Giant . . . Solids", Appl. Phys. Lett. 51(6), Oct. 19, 1987. |
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Patent Grant
4973525
