Iron-nickel-cobalt magnetic powder and tape prepared therefrom

#There has long been a serious problem in providing cobalt-based magnetic powders having good magnetic properties and good corrosion properties. Materials having good magnetic properties tend to have lower corrosion resistance than is desirable, (especially when in the micron- or sub-micron size ranges, i.e., in the making of single-domain particles). When substantial quantities of a material like nickel are used to increase the corrosion resistance, the magnetic properties of a material formed primarily of cobalt or iron markedly.

#A great deal of work has been done on particulate metal powder systems in an attempt to provide powders which are economically practical in magnetic recording systems. A substantial part of this work has been directed to study of systems involving cobalt-based powders and combinations of chromium and or iron with cobalt. In general, the work has resulted in serious practical problems including batch-to-batch variations in product characteristics, and chemical stability under humid air conditions. Some such problems are discussed in the literature, e.g. by Bates and Alstead in IEEE Transactions on Magnetics, MAG-5, December 1969, Page 832. Much of this work was done on a composition having a major amount of iron. One such material (55% iron, 40% cobalt, 5% nickel) thought to be particularly useful by the investigators was not commercially successful, probably because of the aforesaid problems.

#Other work included that of Luborsky. The literature indicates that particles produced by his method of electro-depositing the metal on mercury, were not stable. Luborsky used up 41.5% cobalt in his iron-cobalt systems. His materials, which also would have very low magnetic moment on a volume basis, were described in The Physics Of Magnetic Recording, by C.D. Mee (North Holland Publishing Company, Amsterdam; 1968).

#FIG. 1 is a ternary diagram of the cobalt-nickel-iron system with a shaded area indicated thereon which area corresponds to the alloys of which the novel particles defined herein are formed. This area, A, relates to particles having:

#10 to 33% iron

#50 to 82% cobalt

#The abscissa of the graph of FIGS. 2 range from -2000 to +2000 oersteds and represents the 2000 oersted magnetic field in which the measurements are carried out. The ordinate can be considered as arbitrarily selected to aid demonstration of the difference between tested specimens. (The abscissa in FIG. 2 is reversed, and reads from +2000 to -2000, left to right.)

#FIGS. 2 - must be interpreted with the following in mind: They are in many respects comparative, measured on the same BH meter and consequently characteristics attributable to the electrical characteristics of the meter are a common factor in all the drawings. In general, this is a minor factor. Most useful BH meters will produce very similar curves. Moreover, in making such pictures, as shown in FIG. 3, the distance from the origin (zero field point) to the peaks should be not more than about one-third of the distance from the origin to the maximum applied field. This is to assure that a particular angular function tending to "fatten" these peaks is made negligible.

#However, once these facts are realized, the drawings in FIG. 2 can be used to define highly advantageous and novel features of the invention.