US3859129A - Method of improving the magnetic properties of cobalt substituted magnetite - Google Patents

Method of improving the magnetic properties of cobalt substituted magnetite Download PDF

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US3859129A
US3859129A US257335A US25733572A US3859129A US 3859129 A US3859129 A US 3859129A US 257335 A US257335 A US 257335A US 25733572 A US25733572 A US 25733572A US 3859129 A US3859129 A US 3859129A
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cobalt
film
magnetic
iron
substrate
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Shih-Lu Chen
James A Murphy
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Corning Glass Works
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Corning Glass Works
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F10/00—Thin magnetic films, e.g. of one-domain structure
    • H01F10/08—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers
    • H01F10/10—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition
    • H01F10/18—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being compounds
    • H01F10/20—Ferrites

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  • ABSTRACT [52] 11.8. C1 117/237, 117/235, 117/238, method of improving the magnetic properties of co- 148/108 balt substituted magnetite by magnetizing the material [51] Int. Cl. 1101f 10/00 to the saturation level in the desired direction, and [58] Field of Search 1 17/234-240; then removing the magnetizing field.
  • the material will I 148/108 retain a level of magnetization normally referred to as the remanent state of magnetization or simply rema- [56] References Cited nence.
  • the magnetized material is then subjected to a UMTED STATES PATENTS heat treatment to anneal the material.
  • COERCIVITY PATENTEDJA” 71% 0.5 COBALT TO IRON RATIO (Co/Fe) COERCIVITY (OERSTEIDS) PMENTEUJAH 7:975 3,859 129 SHEET 0am 10' 0 OJ 0.2 0.3 0.4 0.5 COBALT T0 IRON RATIO (Co Fe) Fig. 8
  • PATENTEDJAN H915 SQUARENES RATIO (e /9, ,0 4 01 m SHEET near 10 UNTREATED FILM (PRIOR ART) COBALT TO IRON RATIO (Co Fe) Fig. 9
  • This invention relates to a method of improving the magnetic properties of cobalt substituted magnetite by inducing uniaxial anisotropy in the material in addition to the already present cubic anisotropy.
  • Magnetic and recording storage devices having a film of cobalt substituted magnetite may be used for storing digital information used by data processing computers, or any other analog or digital information where magnetic storage is desired.
  • Cobalt substituted magnetite materials have previously been used in the fabrication of some types of magnetic devices such as permanent magnets.
  • the magnetic qualities of such devices have been improved by heating them to an elevated temperature below the Curie temperature while they were subjected to a magnetic field. I-Iowever,.using such a technique to improve the magnetic qualities of magnetic recording and storage devices is made very difficult, if not impossible, by practical considerations since magnetic recording and storage devices are ordinarily in the shape of a tape, drum, rod or disk.
  • the uniaxial anisotropy must be oriented circumferentially around the drum axis along the cylindrical walls, and to improve the magnetic properties of a disk shaped device the uniaxial anisotropy must be oriented circularly around the axis on the disk surface. Providing magnetic fields to achieve the desired orientation of the uniaxial anisotropy of such devices while they are being heat treated presents very difficult practical problems.
  • an object of this invention to provide a method of inducing uniaxial anisotropy having a desired orientation in a cobalt substituted magnetite material.
  • magnetic properties such as coercivity, hysteresis loop squareness ratio, and resistance to loss of remanence due to abrasion and other external forces may be significantly improved in magnetic devices having cobalt substituted magnetite as the magnetic material by magnetizing the material to the saturation level in a desired direction, and then removing the magnetizing field.
  • the material will retain a level of magnetization normally referred to as remanence.
  • the magnetized material is then subjected to a heat treatment to anneal the material.
  • FIG. 1 is a diagram showing the major hysteresis loop of a device having a cobalt substituted film, which has not been improved by the method of the present invention.
  • FIG. 2 is a diagram showing the effect of variations in the cobalt to iron ratio upon the coercivity and the hysteresis loop squareness ratio of a magnetic device having an unimproved cobalt substituted magnetite film.
  • FIGS. 3-6 are diagrams showing the major parallel and perpendicular hysteresis loops of four magnetic devices having cobalt substituted magnetite films improved by the method of the present invention.
  • FIGS. 7 and 8 are diagrams showing the relationship between coercivity and the cobalt to iron ratio of magnetic devices having cobalt substituted films.
  • FIG. 9 is a diagram showing the relationship between the hysteresis loop squareness ratio and the cobalt to iron ratio of magnetic devices having cobalt substituted magnetite films.
  • FIG. 10 is a diagram showing' the relationship between the loss of remanence in cobalt substituted magnetite films due to external forces, and the cobalt to iron ratio.
  • a magnetic recording and storage device is formed having a non-magnetic substrate to which a magnetic film containing cobalt substituted magnetite is bonded.
  • cobalt substituted magnetite means a magnetic material having a cubic crystalline structure, similar to the crystalline structure of magnetite (Fe 0,) in which cobalt, iron and oxygen are combined according to the formula Co,Fe ,O
  • the magnetic properties of cobalt substituted magnetite may be improved by treating the material according to the method of the present invention for amounts of co- No. 3,015,628 entitled Ferroso-Ferric Oxide for Magnetic Impulse Record Members" issued to Joseph W. Ayers and Robert A. Stephens; US. Pat. No.
  • Kistler, pubcobalt containing compounds include but are not limlished in the Journal of the American Ceramic Society, ited to those Show" in Table The Vapors 0f Ofthe February, 1962, pages 59-68, iron containing compounds listed in Table I may be sat-
  • the magnetic film containing cobalt substituted maglsfactorhy used with the Vapors of any of the cobalt netite may be a solid non-particulate film chemically containing compounds listed in Table I.
  • the iron containing compound ferric chloride FeCl may satisfactorily be used with the cobalt containing compound cobalt chloride (CoCl Depending upon the cobalt containing compound and iron containing compound used, the temperature of the substrate upon which said vapors are allowed to react may be varied from about 200C to an upper limit determined by structural limitations of the substrate. However, in most cases the desirable range will be from about 350C to about 550C.
  • the film resulting from the reaction of the vapors on the heated substrate is a non-magnetic cobalt-iron oxide.
  • the non-magnetic cobalt-iron oxide film is then reduced to a magnetic cobalt substituted magnetite material by subjecting the substrate and non-magnetic cobalt-iron oxide film to a suitable reducing atmosphere, such as a hydrogen and water atmosphere.
  • a suitable reducing atmosphere such as a hydrogen and water atmosphere.
  • Atmospheres particularly suitable for use in this invention include but are not limited to a hydrogen and water mixture, a carbon monoxide and carbon dioxide mixture, and a carbon monoxide and water mixture.
  • An inert gas such as nitrogen, maybe combined with these reducing atmospheres without significantly reducing the effectiveness thereof.
  • An atmosphere of hydrogen and water in combination with nitrogen which is particularly suitable for use with the method of this invention, may be obtained by bubbling a mixture of hydrogen and nitrogen through water.
  • the important consideration of this particular atmosphere is the hydrogen partial pressure to water partial pressure ratio.
  • the nitrogen is substantially inert and acts only as a carrier gas for the water so that the ratio of hydrogen to water in the system is more easily controlled.
  • the allowable range of hydrogen partial pressure to water partial pressure ratio which will produce the desired atmosphere for converting the non-magnetic cobalt-iron oxide will varyas the temperature of the film and substrate combination varies.
  • a hydrogen partial pressure to water partial pressure ratio range of between :1 and ":1 may be used for temperatures between about 300C and 600C. Atmosphere temperatures greater than 600C may be used if the ratio is maintained between about l0:l and l0*:l.
  • the temperature of the film and substrate should be reduced to lessthan about 200C in the shortest possible time to achieve the highest improvement as a result of the present method.
  • FIG. 1 shows the major hysteresis loop of an untreated cobalt substituted magnetite film having a cobalt to iron ratio of about 0.21.
  • Symbol 9 represents the magnetic flux in the material times the film thickness, hereinafter referred to simply as magnetization, which magnetization is brought about by the applied field.
  • magnetization 9 is in gauss centimeters and the applied field H is in oersteds.
  • the maximum remanence is obtained with an applied magnetic field of about 1 100 oersteds since that is the field necessary to magnetize the film to substantially saturation.
  • the coer civity H of such a film is approximately 370 oersteds.
  • the field necessary for saturation will vary depending upon the magnetic properties of the device, however, as a practical matter an external field of between 4000-7500 oersteds may be satisfactorily used for many of the described devices since an excessive field will do no harm whereas an insufficient field will result in an unnecessarily low remanence and, consequently, the improvement as a result of the process of this invention will not be as great as possible.
  • the remanent magnetization in the device aligns the uniaxial anisotropy in the cobalt substituted magnetite film in the same direction thereby eliminating the need for an external field to be applied while the device is undergoing the extreme temperatures encountered during annealing.
  • the device can be magnetized in the desired direction a portion at a time by any suitable means. including the apparatus normally used to record on the magnetic device.
  • magnetic disks may be magnetized substantially to saturation by applying a continuous DC signal to the recording head while rotating the disk in the normal manner in relation to the head. More specifically, the head may be positioned over one track and the disk rotated a full revolution thereunder in the normal manner. The head would then be repositioned over an adjacent track and the disk again rotated a full revolution. This procedure would be continued until all of the tracks of the disk are completely magnetized in the desired direction.
  • Magnetic recording and storage devices having other shapes could similarly be magnetized by the device utilization means. Obviously, equipment specially built for this purpose can also be used.
  • the device is heat treated to anneal the cobalt substituted magnetite film.
  • heat treatment may be satisfactorily carried out in air, but any atmosphere not reactive with the cobalt substituted magnetite or with the substrate material at the annealing temperature may be used.
  • the time necessary for proper annealing varies with temperature and the cobalt to iron ratio. High temperatures require less annealing time and low temperatures require more annealing time. However, it has been found that satisfactory results may be obtained even when the device is annealed for a period of time well in excess of that which is necessary. Good results have been obtained when time period ranged from two hours to 177 hours for temperatures between about 200C and C respectively.
  • the cobalt to iron ratio of cobalt substituted magnetite directly affects some of the magnetic characteristics of the material.
  • FIG. 2 it is seen that the coercivity of a cobalt substituted magnetite film increases and thehysteresis loop squareness ratio decreases as the cobalt to iron ratio increases. The reasons for these changes are not clear. It is believed, however, that the cobalt to iron ratio in the ferromagnetic phase of the film is less than the overall ratio, and that excess cobalt may exist as a second non-ferromagnetic oxide phase or in clusters of paramagnetic material. The presence of either non-ferromagnetic oxide or paramagnetic cobalt clusters would reduce the squareness ratio.
  • cobalt substituted magnetite film was reduced in a reduction atmosphere of hydrogen and water as heretofore described, it is believed, based upon the fact that metallic cobalt is more stable than cobalt oxide under such reduction conditions, that cobalt clusters are likely to be the cause of the low squareness ratio.
  • the method of this invention will improve both the coercivity and hysteresis loop squareness ratio of cobalt substituted magnetite.
  • hysteresis loop squareness ratio when used herein means remanence, 0,, divided by the magnetization occuring when a field of 10,000 oersteds is applied, 9 That is, hysteresis loop squareness ratio G /G
  • FIGS. 3, 4, and 6 show the hysteresis loops of four samples having different cobalt to iron ratios after a 147 hour annealing at about 150C in air. Prior to the annealing, these samples were magnetized to substantially the saturation level in a field of 7500 oersteds.
  • One of the hysteresis loops results when the present device is subjected to a field parallel to the magnetization field which was applied before annealing, and the second loop results when the device is subjected to a field perpendicular to the magnetization field applied before annealing.
  • the hysteresis loop resulting from parallel magnetization and the hysteresis loop resulting from perpendicular magnetization will be referred to as the parallel and perpendicular loops respectively.
  • the parallel and perpendicular loops are quite different except in FIG. 3, where they almost coincide with each other.
  • the parallel loop has a much higher squareness ratio and coercivity than does the perpendicular loop.
  • FIG. 1 illustrates the hysteresis loop of an untreated cobalt substituted magnetite film having a cobalt to iron ratio of 0.21.
  • FIG. 5 illustrates the hysteresis loop of a'treated cobalt substituted magnetite film having a ratio of 0.19.
  • the cobalt to iron ratio in the untreated film illustrated by FIG. 1 is higher than the cobalt to iron ratio of the treated film illustrated by FIG. 5, yet the film illustrated by FIG. 5 has significantly higher coercivity.
  • the parallel and perpendicular hysteresis loops have a significantly higher squareness ratio than does the hysteresis loop of the untreated film.
  • FIGS. 7, 8 and 9 Graphs which illustrate the coercivity and squareness ratio for some films annealed under different conditions are shown in FIGS. 7, 8 and 9.
  • FIG. 7 illustrates the effect of the cobalt to iron ratio on the coercivity of films annealed at 150C according to the method of this invention for different periods of time.
  • FIG. 8 illustrates the effect of the cobalt to iron ratio on the coercivity of films annealed at different temperatures and for different periods of time.
  • FIG. 9 illustrates the effect of the cobalt to iron ratio on the hysteresis loop squareness ratio of films annealed at 150C for different periods of time.
  • FIG. 10 illustrates the effect of the cobalt to iron ratio on the amount ofremanence loss due to abrasion and other external forces upon films annealed at about 150C for different periods of time.
  • Table II The content of FIGS. 7 through 10 are summarized in Table II.
  • the improvement of the coercivity and hysteresis loop squareness ratio as a result of the present treatment may be explained if the likely possibility that the cobalt substituted magnetite film was not microscopically homogeneous is assumed. If such nonhomogeneity existed, it may further be assumed that a homogenization process went on during the heat treatment, and that some of the paramagnetic cobalt clusters diffused to formeither ferromagnetic oxide or both ferromagnetic oxide and non-magnetic iron oxide. Both the normal cubic anisotropic constant and the uniaxial anisotropic constant could increase as a result of such a homogenization process and the increase in ferromagnetic oxide. A decrease in anumber of paramagnetic clusters and an increase in the cubic and uniaxial anisotropic constants would increase both the hysteresis loop squareness ratio and the coercivity of the film.
  • a third and very important improvement of the magnetic properties of a treated cobalt substituted magnetite film is that the tendency to lose remanence due to abrasion or to other types of external forces is greatly reduced.
  • the tendency to lose remanence due to external forces appears to increase as the cobalt to iron ratio in the film increases, and such increase is probably due to the increase of the magnetostriction constant.
  • the tendency to lose remanence due to externally applied forces becomes highly dependent upon the direction of magnetization with respect to the induced uniaxial anisotropy.
  • the percentage of remanence loss is equal to l(6 -6 )/6
  • the high loss of remanence occuring in films magnetized perpendicular to the initial magnetization is in excess of what would be expected if such losses depended only upon the magnetostriction constant. Therefore, it is believed that the excessive loss of remanence of a cobalt substituted magnetite film may be due to the possibility that the effect of an applied force upon a magnetic material depends not only upon the inherent properties of the material, such as the magnetostriction constant and the anisotropic constant, but also upon the physical state of the material itself.
  • a portion of a single crystal will react to an external force quite differently than will a piece of polycrystalline material or a thin film. The difference arises from mechanical interaction between neighboring particles and between particles and the substrate.
  • a single crystal can change its shape or dimension without producing internal strain. In a polycrystalline material or thin film, however, the situation is quite different. Since the crystals are tightly bound to the substrate and tightly packed against each other, they can no longer change their shape and dimensions freely. Therefore, when a film is cooled down from the high temperature at which it was formed, the magnetization in each crystal will be oriented in a direction such that the total energy of the film as a whole will be minimum. This total energy includes the crystalline anisotropic energy, magnetostriction energy, and elastic energy.
  • FIG. 5 illustrates the parallel and perpendicular hysteresis loops obtained from the device of this example.
  • a method of improving magnetic properties of a magnetic device comprising the steps of forming a cobalt substituted magnetite film having a cobalt to iron ratio of between about 0.0345 and about 0.665, said film being bonded to a nonmagnetic substrate, thereafter subjecting said cobalt substituted magnetite film to a magnetic field having sufficient field strength and an orientation to magnetize said film in a desired direction,
  • said non-magnetic substrate is formed of material selected from the group consisting of anodized aluminum, glass-ceramic, glass, and ceramic.
  • forming a cobalt substituted magnetite film comprises the steps of heating said substrate to a temperature of between about 350C and about 550C, exposing a surface of said heated substrate to vapors of a cobalt containing compound and simultaneously to vapors of an iron containing compound, to form a film of non-magnetic cobalt-iron oxide chemically bonded to said substrate, and thereafter heating said film of non-magnetic cobalt-iron oxide to a temperature of between about 300C and about 600C in a reducing atmosphere to reduce the materialof said film to cobalt substituted magnetite.
  • said cobalt containing compound is selected from the group consisting of cobalt nitrosyltricarbonyl, cobaltocene, cobaltic acetylacetonate, cobaltous acetylacetonate, cobaltic hexafluoroacetylacetonate, and cobaltous hexafluoroac'etylacetonate
  • said iron containing compound is selected from the group consisting of iron pentacarbonyl, ferrocene, ferric acetylacetonate, ferrous acetylacetonate, ferric hexafluoroacetylacetonate, and ferrous hexafluoroacetylacetonate.
  • said nonmagnetic substrate is made of an ion-exchange strengthened glass.

Abstract

A method of improving the magnetic properties of cobalt substituted magnetite by magnetizing the material to the saturation level in the desired direction, and then removing the magnetizing field. The material will retain a level of magnetization normally referred to as the remanent state of magnetization or simply remanence. The magnetized material is then subjected to a heat treatment to anneal the material. The above process significantly improves coercivity, hysteresis loop squareness ratio, and resistance to remanence loss due to external forces.

Description

United States. Patent 1191 Chen et a1. 1 1 Jan. 7, 1975 [5 METHOD OF IMPROVING THE MAGNETIC 3,546,675 12/1970 Che Chung-Chow ct 111.. 117/235 x OP S O COBALT SUBSTITUTED 3,573,980 4/1971 Haller etkal. 117/238 .620,841 11/1971 Comstoc et a1 117/235 X MAGNETITE 3,703,411 11/1972 Mclezoglu 117/235 X [75] Inventors: Shih-Lu Chen; James A. Murphy, 5.725.126 4/1973 Hallcr c1111. 117/235 both of Painted Post, N.Y.
Primar E.\'aminer-Williz1m D. Martin 73 A. c G1 k Y ss1gnee Nogiimg ass Wor 5, Coming Assistant E.mminerBcrnard D. Pianalto Attorney, Agent, or FirmWalter S. Zcbrowski; Flledi y 1972 Clarence R. Patty, Jr. [21] Appl. No.: 257,335
[57] ABSTRACT [52] 11.8. C1 117/237, 117/235, 117/238, method of improving the magnetic properties of co- 148/108 balt substituted magnetite by magnetizing the material [51] Int. Cl. 1101f 10/00 to the saturation level in the desired direction, and [58] Field of Search 1 17/234-240; then removing the magnetizing field. The material will I 148/108 retain a level of magnetization normally referred to as the remanent state of magnetization or simply rema- [56] References Cited nence. The magnetized material is then subjected to a UMTED STATES PATENTS heat treatment to anneal the material. The above pro 2 919 207 12/1959 Scholzel 117/236 cess significantly improves coercivity, hysteresis loop 3:047:423 7/1962 Eggenberge r etaljziiliiiii: 117/238 Squareness ratio and resistance remanence loss due 3,092,510 6/1963 Edelman 117/238 exter forces- 3,374,113 3/1968 Chang et a1. 117/238 UX 3.393.982 7/1968 Fisher et a1. 117/23811x 12 10 Drawmg Fgures e 0065 MAX/CM H (OERSTEDS) APPLIED FIELD 9 (GAUSS-CENTIMETERS) I PATENTEDJAN 71915 3.859.129
SHEET UlUF1O E5 3 5' 0 ,Q) l- Q g a: .9, E
O '(sazuawlmaa ssnvs) e PATENTEDJAN 71915 R 3,859,129
sum near 10 COERCIVITY 0.8 -5o0 g 9 :2 *5 co 0: 0 0:
0.7 400 g w v' 0') Lil g HYSTERSIS LOOP g SQUARENESS RATIO w 0.5 zoo o COBALT to IRON RATIO (Co/ Fe) (PRIOR ART),
PATENTEU 3,859,129
' sum 0m 10 Co/ Fe 0.|2
'0, (PARALLEL) H (PERPEN- DICULAR) HC(PARALLEL) IO H (OERSTEDS) PARALLEL 100p e =009|5 MAX/CM Gr/G =O.682 H 490 Oe PERPENDICULAR loo p e 0.0885 MAX/CM Fig. 4
COERCIVITY (OERSTEDS) PATENTEDJA" 71% 0.5 COBALT TO IRON RATIO (Co/Fe) COERCIVITY (OERSTEIDS) PMENTEUJAH 7:975 3,859 129 SHEET 0am 10' 0 OJ 0.2 0.3 0.4 0.5 COBALT T0 IRON RATIO (Co Fe) Fig. 8
PATENTEDJAN H915 SQUARENES RATIO (e /9, ,0 4 01 m SHEET near 10 UNTREATED FILM (PRIOR ART) COBALT TO IRON RATIO (Co Fe) Fig. 9
PAIENIEB M 3.859.129
, i l 2 PERCENTAGE OF REMANENCE l m SHEET IUUF 10 UNANNEALED FILM (PRIOR ART) Fig. /0
BACKGROUND OF THE INVENTION I. Field of the Invention This invention relates to a method of improving the magnetic properties of cobalt substituted magnetite by inducing uniaxial anisotropy in the material in addition to the already present cubic anisotropy. Magnetic and recording storage devices having a film of cobalt substituted magnetite may be used for storing digital information used by data processing computers, or any other analog or digital information where magnetic storage is desired.
II. Description of the Prior Art It is known by those skilled in the art that heating cobalt substituted magnetite material to an elevated temperature less than the Curie temperature of the material while the material is being subjected to a magnetic field will result in a uniaxial anisotropy being induced in the material in the direction of the magnetic field. The magnetic field applied during heating of the material does not directly induce the resulting uniaxial anisotropy of the material, but merely aligns the magnetization of each crystal or each domain in substantially the same direction. It is understood that when the material is subjected to an elevated temperature less than the Curie temperature, a uniaxial anisotropy is induced in each crystal of a polycrystalline material or each domain of a single crystal whether or not a magnetic field is applied. If the magnetic field is not applied, the uniaxial anisotropy of each crystal or domain is induced in a random direction. The uniaxial anisotropy superimposes itself on the normal cubic anisotropy. Additional information on this phenomena is available in the following publications: Physical Review, Volume 99, page 1788, 1955, by R. M. Bozorth, E. F. Tilden, and A. J. Williams; Proceedings of the Institute of Electrical En gineering, London, Volume 104, Part B Supplement 7, page 412, 1957, by Wijn, Van der Heide, and Fast; Journal of the Physical Society of Japan, Volume 13, page 58, 1958, by Shuichi Lida, I-Iisashi Sekizawa, and Yoshimichi Siyama; Physical Review, Volume 108, page 271, 1957, by R. F. Penoyer and L. R. Bickford, Jr.; and Journal of Applied Physics, Volume 29, page 441, 1958, by L. R. Bickford, Jr., J. M. Brownlaw and R. F. Penoyer.
Cobalt substituted magnetite materials have previously been used in the fabrication of some types of magnetic devices such as permanent magnets. The magnetic qualities of such devices have been improved by heating them to an elevated temperature below the Curie temperature while they were subjected to a magnetic field. I-Iowever,.using such a technique to improve the magnetic qualities of magnetic recording and storage devices is made very difficult, if not impossible, by practical considerations since magnetic recording and storage devices are ordinarily in the shape of a tape, drum, rod or disk. To improve the magnetic properties of a drum shaped device, for example, the uniaxial anisotropy must be oriented circumferentially around the drum axis along the cylindrical walls, and to improve the magnetic properties of a disk shaped device the uniaxial anisotropy must be oriented circularly around the axis on the disk surface. Providing magnetic fields to achieve the desired orientation of the uniaxial anisotropy of such devices while they are being heat treated presents very difficult practical problems.
SUMMARY OF THE INVENTION It is therefore, an object of this invention to provide a method of inducing uniaxial anisotropy having a desired orientation in a cobalt substituted magnetite material.
It is a further object of this invention to provide a simple and economical method ofinducing uniaxial anisotropy having a desired orientation in a magnetic recording and storage device employing cobalt substituted magnetite material as the storage medium, which method overcomes the heretofore noted disadvantages.
Briefly, according to this invention magnetic properties such as coercivity, hysteresis loop squareness ratio, and resistance to loss of remanence due to abrasion and other external forces may be significantly improved in magnetic devices having cobalt substituted magnetite as the magnetic material by magnetizing the material to the saturation level in a desired direction, and then removing the magnetizing field. The material will retain a level of magnetization normally referred to as remanence. The magnetized material is then subjected to a heat treatment to anneal the material.
Additional objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description and attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the major hysteresis loop of a device having a cobalt substituted film, which has not been improved by the method of the present invention.
FIG. 2 is a diagram showing the effect of variations in the cobalt to iron ratio upon the coercivity and the hysteresis loop squareness ratio of a magnetic device having an unimproved cobalt substituted magnetite film.
FIGS. 3-6 are diagrams showing the major parallel and perpendicular hysteresis loops of four magnetic devices having cobalt substituted magnetite films improved by the method of the present invention.
FIGS. 7 and 8 are diagrams showing the relationship between coercivity and the cobalt to iron ratio of magnetic devices having cobalt substituted films.
FIG. 9 is a diagram showing the relationship between the hysteresis loop squareness ratio and the cobalt to iron ratio of magnetic devices having cobalt substituted magnetite films.
FIG. 10 is a diagram showing' the relationship between the loss of remanence in cobalt substituted magnetite films due to external forces, and the cobalt to iron ratio.
DETAILED DESCRIPTION A magnetic recording and storage device is formed having a non-magnetic substrate to which a magnetic film containing cobalt substituted magnetite is bonded. As used herein, the term cobalt substituted magnetite means a magnetic material having a cubic crystalline structure, similar to the crystalline structure of magnetite (Fe 0,) in which cobalt, iron and oxygen are combined according to the formula Co,Fe ,O The magnetic properties of cobalt substituted magnetite may be improved by treating the material according to the method of the present invention for amounts of co- No. 3,015,628 entitled Ferroso-Ferric Oxide for Magnetic Impulse Record Members" issued to Joseph W. Ayers and Robert A. Stephens; US. Pat. No. 3.047.505 entitled Magnetic Recording Media" issued toArthur theainount of cobalt in magnetite'by referring to the 5 Miller; and U.S. Pat. No. 3,330,693 entitled Method value of x, such amount is herein indicated by the coof Making a Magnetic Record Member with Encapsubalt to iron ratio, or simply Co/Fe. The cobalt to iron lated Ferromagnetic Particles in a Binder and Resulting ratio is related to x by the equation Co/Fe =x/3-x. For Product issued to George C. Rumberger. Techniques example, where x equals 0.1, Co/Fe 0.l/30.l or for fabricating devices having a solid non-particulate 0.0345; and where x equals 1.2, Co/Fe= l.2/3l.2 or magnetic film chemically bonded to a substrate, al- 0.665. Although films having a Co/Fe between a low though available, are not as well known. However, invalue of ab0ut 0.()345 a d a hi h value f b t 0,665 formation concerning such techniques may be found in may be improved by the method of this invention, the 2i9l9,207 entitled Method of pp y most significant improvement occurs in films having a a Ferromagnetic surface to a Base Utilizing Iron C Co/Fe of between about 0.1 and 0,25 15 bonyl and oxygen issued to Karl Schol'zel, and in the The substrate or support member may have any suittwo P e applicfltlohs entitled f of Making a able form such as a tape, disk, rod, drum or the like, Magnet": keciordlhg and storage'Devlce by James and may be formed from any suitable non-magnetic P Y Halaby and Neal Kenny material that can withstand the temperatures encoun- 1511356 1795542 and tered in the method of this invention without damage. 151,388 both filed 1971' Examples of such materials are vinyls, plastics, anod- A methoq Pmducmg a cobalt subsmuted magne' ized aluminum, glass-ceramic,,glass, ceramic and the film chenllcanyfbonded to the .substhate like. The present invention is not limited to any specific w Pamcularly Stumble or the present mvemlon substrate material. For magnetic devices not requiring as 0 a highly flexible substrate, a particularly suitable mate- The vapors of an iron containing compound that will rial for forming a disk, rod, drum or the like is ionnot decompose when vaporizedmnd the p s a exchange strengthened glass or glass-ceramic. A basic balt containing compound that will not decompose discussion of ion-exchange strengthening processes is When v p z are transported o a a ed u strate found in Stresses in Glass Prod ced b N JJ if where the vapors are allowed to react. Such iron and Exchange of Monovalent Ions by S. F. Kistler, pubcobalt containing compounds include but are not limlished in the Journal of the American Ceramic Society, ited to those Show" in Table The Vapors 0f Ofthe February, 1962, pages 59-68, iron containing compounds listed in Table I may be sat- The magnetic film containing cobalt substituted maglsfactorhy used with the Vapors of any of the cobalt netite may be a solid non-particulate film chemically containing compounds listed in Table I.
Table I Cobalt Containing Materials Iron Containing Materials cobalt nitrosyltricarbonyl iron pentacarbony1-Fe(CO) 5 Co( O)3NO cobaltocene-Co (05115) 2 terrocene-Fe (0 115) 2 cobaltic acetylacetonate eobaltous acetylacetonate cobaltie hexafluoroacetylacetonate cobaltous hexafluoroacetylaeetonate bonded to thesubstrate, or maybe particles of the cobalt substituted magnetite material bonded to each other and to the substrate by binder or filler materials such as epoxies, urethanes, vinyls, and the like. Techferric acetylacetonate ferrous acetylacetonate ferric hexafluoroacetylacetonate ferrous hexafluoroaeetylacetonate In addition, the iron containing compound ferric chloride (FeCl may satisfactorily be used with the cobalt containing compound cobalt chloride (CoCl Depending upon the cobalt containing compound and iron containing compound used, the temperature of the substrate upon which said vapors are allowed to react may be varied from about 200C to an upper limit determined by structural limitations of the substrate. However, in most cases the desirable range will be from about 350C to about 550C. The film resulting from the reaction of the vapors on the heated substrate is a non-magnetic cobalt-iron oxide. The non-magnetic cobalt-iron oxide film is then reduced to a magnetic cobalt substituted magnetite material by subjecting the substrate and non-magnetic cobalt-iron oxide film to a suitable reducing atmosphere, such as a hydrogen and water atmosphere. ,The reduction is accomplished by heating the film and substrate combination to a temperature of between 300C and a maximum temperature determinedby structural limitations of the substrate while maintaining the combination in a reducing atmosphere.
Atmospheres particularly suitable for use in this invention include but are not limited to a hydrogen and water mixture, a carbon monoxide and carbon dioxide mixture, and a carbon monoxide and water mixture. An inert gas, such as nitrogen, maybe combined with these reducing atmospheres without significantly reducing the effectiveness thereof. An atmosphere of hydrogen and water in combination with nitrogen, which is particularly suitable for use with the method of this invention, may be obtained by bubbling a mixture of hydrogen and nitrogen through water. The important consideration of this particular atmosphere is the hydrogen partial pressure to water partial pressure ratio. The nitrogen. is substantially inert and acts only as a carrier gas for the water so that the ratio of hydrogen to water in the system is more easily controlled. The allowable range of hydrogen partial pressure to water partial pressure ratio which will produce the desired atmosphere for converting the non-magnetic cobalt-iron oxide will varyas the temperature of the film and substrate combination varies. A hydrogen partial pressure to water partial pressure ratio range of between :1 and ":1 may be used for temperatures between about 300C and 600C. Atmosphere temperatures greater than 600C may be used if the ratio is maintained between about l0:l and l0*:l. After reduction is completed, the temperature of the film and substrate should be reduced to lessthan about 200C in the shortest possible time to achieve the highest improvement as a result of the present method.
g The magnetic device as described is subjected to a magnetic field to magnetize the film in the desired di rection to substantially the saturation level of the material. The magnetic field strength required to magnetize the device to the saturation level will depend upon the magnetic properties of the device. For example, FIG. 1 shows the major hysteresis loop of an untreated cobalt substituted magnetite film having a cobalt to iron ratio of about 0.21. Symbol 9 represents the magnetic flux in the material times the film thickness, hereinafter referred to simply as magnetization, which magnetization is brought about by the applied field. In FIG. 1, magnetization 9 is in gauss centimeters and the applied field H is in oersteds. From FIG. 1, it can be seen that the maximum remanence is obtained with an applied magnetic field of about 1 100 oersteds since that is the field necessary to magnetize the film to substantially saturation. As can also be seen from FIG. 1, the coer civity H of such a film is approximately 370 oersteds. As heretofore noted, the field necessary for saturation will vary depending upon the magnetic properties of the device, however, as a practical matter an external field of between 4000-7500 oersteds may be satisfactorily used for many of the described devices since an excessive field will do no harm whereas an insufficient field will result in an unnecessarily low remanence and, consequently, the improvement as a result of the process of this invention will not be as great as possible. After the external magnetic field has been removed the remanent magnetization in the device aligns the uniaxial anisotropy in the cobalt substituted magnetite film in the same direction thereby eliminating the need for an external field to be applied while the device is undergoing the extreme temperatures encountered during annealing.
ln employing the method of the present invention. the device can be magnetized in the desired direction a portion at a time by any suitable means. including the apparatus normally used to record on the magnetic device. For example, magnetic disks may be magnetized substantially to saturation by applying a continuous DC signal to the recording head while rotating the disk in the normal manner in relation to the head. More specifically, the head may be positioned over one track and the disk rotated a full revolution thereunder in the normal manner. The head would then be repositioned over an adjacent track and the disk again rotated a full revolution. This procedure would be continued until all of the tracks of the disk are completely magnetized in the desired direction. Magnetic recording and storage devices having other shapes could similarly be magnetized by the device utilization means. Obviously, equipment specially built for this purpose can also be used.
After the desired remanence and alignment is obtained, the device is heat treated to anneal the cobalt substituted magnetite film. Such heat treatment may be satisfactorily carried out in air, but any atmosphere not reactive with the cobalt substituted magnetite or with the substrate material at the annealing temperature may be used. The time necessary for proper annealing varies with temperature and the cobalt to iron ratio. High temperatures require less annealing time and low temperatures require more annealing time. However, it has been found that satisfactory results may be obtained even when the device is annealed for a period of time well in excess of that which is necessary. Good results have been obtained when time period ranged from two hours to 177 hours for temperatures between about 200C and C respectively. If the temperature is below about 95C, annealing is so slow that the total required time is excessive and therefore unsatisfactory. On the other hand, if the temperature is above about 200C, process control becomes more difficult, and the results become less predictable since the cobalt substituted magnetite begins to becomechemically unstable and may convert to a nonmagnetic oxide. It has been found that excellent and consistent results can be obtained by using a temperature of between about C and C for a time period of about 147 hours.
As heretofore noted, the cobalt to iron ratio of cobalt substituted magnetite directly affects some of the magnetic characteristics of the material. Referring to FIG. 2, it is seen that the coercivity of a cobalt substituted magnetite film increases and thehysteresis loop squareness ratio decreases as the cobalt to iron ratio increases. The reasons for these changes are not clear. It is believed, however, that the cobalt to iron ratio in the ferromagnetic phase of the film is less than the overall ratio, and that excess cobalt may exist as a second non-ferromagnetic oxide phase or in clusters of paramagnetic material. The presence of either non-ferromagnetic oxide or paramagnetic cobalt clusters would reduce the squareness ratio. If the cobalt substituted magnetite film was reduced in a reduction atmosphere of hydrogen and water as heretofore described, it is believed, based upon the fact that metallic cobalt is more stable than cobalt oxide under such reduction conditions, that cobalt clusters are likely to be the cause of the low squareness ratio.
The method of this invention will improve both the coercivity and hysteresis loop squareness ratio of cobalt substituted magnetite. The term hysteresis loop squareness ratio when used herein means remanence, 0,, divided by the magnetization occuring when a field of 10,000 oersteds is applied, 9 That is, hysteresis loop squareness ratio G /G FIGS. 3, 4, and 6 show the hysteresis loops of four samples having different cobalt to iron ratios after a 147 hour annealing at about 150C in air. Prior to the annealing, these samples were magnetized to substantially the saturation level in a field of 7500 oersteds. FIGS. 3, 4, 5 and 6 each contain two hysteresis loops. One of the hysteresis loops results when the present device is subjected to a field parallel to the magnetization field which was applied before annealing, and the second loop results when the device is subjected to a field perpendicular to the magnetization field applied before annealing. Hereinafter, the hysteresis loop resulting from parallel magnetization and the hysteresis loop resulting from perpendicular magnetization will be referred to as the parallel and perpendicular loops respectively. The parallel and perpendicular loops are quite different except in FIG. 3, where they almost coincide with each other. The parallel loop has a much higher squareness ratio and coercivity than does the perpendicular loop. v
FIG. 1 illustrates the hysteresis loop of an untreated cobalt substituted magnetite film having a cobalt to iron ratio of 0.21. FIG. 5 illustrates the hysteresis loop of a'treated cobalt substituted magnetite film having a ratio of 0.19. Although the cobalt to iron ratios are not identical, they are close enough to illustrate the improvement in the coercivity and hysteresis loop squareness ratiowhich results when the magnetic devices are treated in accordance with the present invention. The cobalt to iron ratio in the untreated film illustrated by FIG. 1 is higher than the cobalt to iron ratio of the treated film illustrated by FIG. 5, yet the film illustrated by FIG. 5 has significantly higher coercivity. In addition, the parallel and perpendicular hysteresis loops have a significantly higher squareness ratio than does the hysteresis loop of the untreated film.
Graphs which illustrate the coercivity and squareness ratio for some films annealed under different conditions are shown in FIGS. 7, 8 and 9. FIG. 7 illustrates the effect of the cobalt to iron ratio on the coercivity of films annealed at 150C according to the method of this invention for different periods of time. FIG. 8 illustrates the effect of the cobalt to iron ratio on the coercivity of films annealed at different temperatures and for different periods of time. FIG. 9 illustrates the effect of the cobalt to iron ratio on the hysteresis loop squareness ratio of films annealed at 150C for different periods of time. FIG. 10 illustrates the effect of the cobalt to iron ratio on the amount ofremanence loss due to abrasion and other external forces upon films annealed at about 150C for different periods of time. The content of FIGS. 7 through 10 are summarized in Table II.
Table Il-Continued Annealing Magnetization Figure Curve Temp. C Time Hrs. Direction 7 E 150 I8 Perpendicular 8 F 200 2 Parallel 8 r G 200 2 Perpendicular 8 H 177 Parallel 8 l 95 I77 Perpendicular 9 .l 147 Parallel I 9 K 150 18 Parallel 9 L 150 I47 Perpendicular 10 M 150 18 Perpendicular l0 N 150 82 Perpendicular l0 0 Not Magnetized 10 P 150 18 Parallel 10 Q 150 82 Parallel The effects of these different annealing conditions can be summarized as follows: (A) The coercivity and the squareness ratio for both the parallel and perpendicular loops of an annealed film are higher than those for a non-annealed sample with a comparable cobalt to iron ratio. (B) Films annealed at high temperatures have higher coercivity than those annealed at lower temperatures; (C) The coercivity of the material is significantly higher when magnetized parallel to the initial magnetic field than when the material is magnetized perpendicular to the initial magnetic field. (D) Films annealed at lower temperatures seem to have a slightly higher squareness ratio than those annealed at higher temperatures.
The improvement of the coercivity and hysteresis loop squareness ratio as a result of the present treatment may be explained if the likely possibility that the cobalt substituted magnetite film was not microscopically homogeneous is assumed. If such nonhomogeneity existed, it may further be assumed that a homogenization process went on during the heat treatment, and that some of the paramagnetic cobalt clusters diffused to formeither ferromagnetic oxide or both ferromagnetic oxide and non-magnetic iron oxide. Both the normal cubic anisotropic constant and the uniaxial anisotropic constant could increase as a result of such a homogenization process and the increase in ferromagnetic oxide. A decrease in anumber of paramagnetic clusters and an increase in the cubic and uniaxial anisotropic constants would increase both the hysteresis loop squareness ratio and the coercivity of the film.
A third and very important improvement of the magnetic properties of a treated cobalt substituted magnetite film is that the tendency to lose remanence due to abrasion or to other types of external forces is greatly reduced. The tendency to lose remanence due to external forces appears to increase as the cobalt to iron ratio in the film increases, and such increase is probably due to the increase of the magnetostriction constant. However, after the magnetic properties of a film have been improved by the method of the present invention, the tendency to lose remanence due to externally applied forces becomes highly dependent upon the direction of magnetization with respect to the induced uniaxial anisotropy. For example, when a film is magnetized in the same direction'as the induced uniaxial anisotropy, the remanence loss due to external forces is much less than when the treated film is magnetized perpendicular to the direction of the induced uniaxial anisotropy. If the film was annealed without being initially magnetized, the tendency to lose remanence will be the same no matter in what direction the film is subsequently magnetized, and this loss will be intermediate to that of losses when the film is initially magnetized in either the parallel and perpendicular directions. The results of several samples tested for remanence losses are shown in FIG. 10. The values 9, and fi represent the remanence before and after external forces were applied respectively. Therefore, the percentage of remanence loss is equal to l(6 -6 )/6 Even though cobalt substituted magnetite material has a high magnetostriction constant, the high loss of remanence occuring in films magnetized perpendicular to the initial magnetization is in excess of what would be expected if such losses depended only upon the magnetostriction constant. Therefore, it is believed that the excessive loss of remanence of a cobalt substituted magnetite film may be due to the possibility that the effect of an applied force upon a magnetic material depends not only upon the inherent properties of the material, such as the magnetostriction constant and the anisotropic constant, but also upon the physical state of the material itself. A portion of a single crystal will react to an external force quite differently than will a piece of polycrystalline material or a thin film. The difference arises from mechanical interaction between neighboring particles and between particles and the substrate. A single crystal can change its shape or dimension without producing internal strain. In a polycrystalline material or thin film, however, the situation is quite different. Since the crystals are tightly bound to the substrate and tightly packed against each other, they can no longer change their shape and dimensions freely. Therefore, when a film is cooled down from the high temperature at which it was formed, the magnetization in each crystal will be oriented in a direction such that the total energy of the film as a whole will be minimum. This total energy includes the crystalline anisotropic energy, magnetostriction energy, and elastic energy. When the film is magnetized, an internal strain will be created which will increase the total energy of the film because the crystals are not free to change their dimensions. This type of internal strain, although negligible in some material, is not negligible in cobalt substituted magnetite, and is believed to be responsible for the high loss in remanence when an external force is applied to a non-annealed sample. However, if the magnetized film is annealed, some of the internal strain is believed to be relieved. Consequently, when the film is subsequently magnetized in the same direction as the initial magneti zation, internal strain is much less than it would be if the film was subsequently magnetized in a direction perpendicular to the initial magnetization. The difference in internal strain is believed to explain why the loss in remanence varies so greatly with the direction of magnetization.
Specific Example until an approximately 3000 A thickness film of nonmagnetic cobaltiron oxide was deposited thereon. The film was then reduced to cobalt substituted magnetite by being subjected to a water and hydrogen atmosphere at 450C for 1% hours. An atmosphere having a hydrogen partial pressure to water partial pressure ratio of about 2.421 was used for reducing the film. The atmosphere was obtained by bubbling a mixture of 8% by volume of hydrogen and 92% by volume of nitrogen through water, while said hydrogen, nitrogen and water were maintained at approximately 25 C. The magnetic device was then magnetized to the saturation level with a circumferential orientation. The magnetic device was then annealed in air at 150C for M7 hours. FIG. 5 illustrates the parallel and perpendicular hysteresis loops obtained from the device of this example.
Although the present invention has been described with respect to specific details of certain embodiments thereof, it is not intended that such specific details be limitations upon the scope of the invention except insofar as is set forth in the following claims.
We claim:
1. A method of improving magnetic properties of a magnetic device comprising the steps of forming a cobalt substituted magnetite film having a cobalt to iron ratio of between about 0.0345 and about 0.665, said film being bonded to a nonmagnetic substrate, thereafter subjecting said cobalt substituted magnetite film to a magnetic field having sufficient field strength and an orientation to magnetize said film in a desired direction,
removing said film from said magnetic field, said film retaining a remanent level of magnetization in said desired direction, and thereafter annealing said magnetized film at a temperature of between about 95 C and about 200C for at least about 2 hours.
2. The method of claim 1 wherein said cobalt substituted magnetite film has a cobalt to iron ratio of between about 0.1 and about 0.25.
3. The method of claim 1 wherein said magnetic field strength is sufficient to magnetize said material to the saturation level. A
4. The method of claim 1 wherein said annealing is performed at a temperature between about C and about C.
5. The method of claim 1 wherein said film is annealed for a period of time between about two hours and about 177 hours.
6. The method of claim 1 wherein said annealing is performed in air.
7. The method of claim 1 wherein said cobalt substituted magnetite film has a cobalt to iron ratio of between about 0.1 and about 0.25, said magnetic field strength is sufficient to magnetize said film to the saw ration level, and said annealing is performed at a temperature between about 150C and about 160C for a period of time between about 2 hours and about 147 hours.
8. The method of claim 1 wherein said non-magnetic substrate is formed of material selected from the group consisting of anodized aluminum, glass-ceramic, glass, and ceramic.
9. The method of claim 1 wherein forming a cobalt substituted magnetite film comprises the steps of heating said substrate to a temperature of between about 350C and about 550C, exposing a surface of said heated substrate to vapors of a cobalt containing compound and simultaneously to vapors of an iron containing compound, to form a film of non-magnetic cobalt-iron oxide chemically bonded to said substrate, and thereafter heating said film of non-magnetic cobalt-iron oxide to a temperature of between about 300C and about 600C in a reducing atmosphere to reduce the materialof said film to cobalt substituted magnetite. 10. The method of claim 9 wherein said cobalt containing compound is selected from the group consisting of cobalt nitrosyltricarbonyl, cobaltocene, cobaltic acetylacetonate, cobaltous acetylacetonate, cobaltic hexafluoroacetylacetonate, and cobaltous hexafluoroac'etylacetonate, and said iron containing compound is selected from the group consisting of iron pentacarbonyl, ferrocene, ferric acetylacetonate, ferrous acetylacetonate, ferric hexafluoroacetylacetonate, and ferrous hexafluoroacetylacetonate.
11. The method of claim 9 wherein said cobalt containing compound is cobalt chloride, and the iron containing compound is ferric chloride.
12. The method of claim 9 wherein said nonmagnetic substrate is made of an ion-exchange strengthened glass.

Claims (12)

1. A method of improving magnetic properties of a magnetic device comprising the steps of forming a cobalt substituted magnetite film having a cobalt to iron ratio of between about 0.0345 and about 0.665, said film being bonded to a non-magnetic substrate, thereafter subjecting said cobalt substituted magnetite film to a magnetic field having sufficient field strength and an orientation to magnetize said film in a desired direction, removing said film from said magnetic field, said film retaining a remanent level of magnetization in said desired direction, and thereafter annealing said magnetized film at a temperature of between about 95* C and about 200*C for at least about 2 hours.
2. The method of claim 1 wherein said cobalt substituted magnetite film has a cobalt to iron ratio of between about 0.1 and about 0.25.
3. The method of claim 1 wherein said magnetic field strength is sufficient to magnetize said material to the saturation level.
4. The method of claim 1 wherein said annealing is performed at a temperature between about 150*C and about 160*C.
5. The method of claim 1 wherein said film is annealed for a period of time between about two hours and about 177 hours.
6. The method of claim 1 wherein said annealing is performed in air.
7. The method of claim 1 wherein said cobalt substituted magnetite film has a cobalt to iron ratio of between about 0.1 and about 0.25, said magnetic field strength is sufficient to magnetize said film to the saturation level, and said annealing is performed at a temperature between about 150*C and about 160*C for a period of time between about 2 hours and about 147 hours.
8. The method of claim 1 wherein said non-magnetic substrate is formed of material selected from the group consisting of anodized aluminum, glass-ceramic, glass, and ceramic.
9. The method of claim 1 wherein forming a cobalt substituted magnetite film comprises the steps of heating said substrate to a temperature of between about 350*C and about 550*C, exposing a surface of said heated substrate to vapors of a cobalt containing compound and simultaneously to vapors of an iron containing compound, to form a film of non-magnetic cobalt-iron oxide chemically bonded to said substrate, and thereafter heating said film of non-magnetic cobalt-iron oxide to a temperature of between about 300*C and about 600*C in a reducing atmosphere to reduce the material of said film to cobalt substituted magnetite.
10. The method of claim 9 wherein said cobalt containing compound is selected from the group consisting of cobalt nitrosyltricarbonyl, cobaltocene, cobaltic acetylacetonate, cobaltous acetylacetonate, cobaltic hexafluoroacetylacetonate, and cobaltous hexafluoroacetylacetonate, and said iron containing compound is selected from the group consisting of iron pentacarbonyl, ferrocene, ferric acetylacetonate, ferrous acetylacetonate, ferric hexafluoroacetylacetonate, and ferrous hexafluoroacetylacetonate.
11. The method of claim 9 wherein said cobalt containing compound is cobalt chloride, and the iron containing compound is ferric chloride.
12. THE METHOD OF CLAIM 9 WHEREIN SAID NON-MAGNETIC SUBSTRATE IS MADE OF AN ION-EXCHAGE STRENGTHENED GLASS.
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FR2533731A1 (en) * 1982-09-27 1984-03-30 Philips Nv THERMOMAGNETO-OPTICAL MEMORY DEVICE AND ITS RECORDING MEDIUM
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