Techniques for Preparing Magnetic Particles Having Utility in Recording Media

An alloy having a composition consisting essentially of 15% iron, 15% nickel, 0.2% magnesium and the balance essentially copper was prepared. A sample of the alloy was homogenized at 1100.degree. C. for 24 hours and cooled. The alloy sample was then cold rolled about 70%, heat treated at 1100.degree. C. for 2 hours and rapidly cooled to insure homogeneity. Prior to being subjected to an aging treatment, the sample was further cold rolled to obtain a 50% reduction. Then, the material was thermally aged at 650.degree. C. for 4 hours to effect decomposition of the homogenized material into ferromagnetic particles in a copper-rich matrix.

The material thus prepared was broken into two groups. The copper-rich matrix in each group was electrolytically dissolved using an aqueous pyrophosphate solution containing 1.375M potassium pyrophosphate, 0.3M nickel sulfamate, and 0.125M copper pyrophosphate. The solution had a pH of 9 and was kept at a temperature of 50.degree. C. The sample forming the first group was immersed in the pyrophosphate solution and a current density of 12mA/cm.sup.2 was applied to a cathode and an anode also immersed in the solution. The magnetic particles recovered from this first group exhibited a saturation magntization of 108.6 EMU/g and a coercive field of 644 Oe.

The sample forming the second group was immersed in the same pyrophosphate solution and a current density of 18 mA/cm.sup.2 was applied to the electrodes. The magnetic particles recovered from this group exhibited a saturation magnetization of 98 EMU/g and a coercive field of 690 Oe.

It is believed that the foregoing example illustrates the improved magnetic particles which can be obtained by the present invention.

While it is preferred that the thermal aging step be the final processing step before dissolution of the matrix, it may be necessary with some alloy systems to further cold work the material after the thermal aging treatment to assist the dissolution process.

While a particular technique for forming magnetic particles has been illustrated, it should be recognized that the pyrophosphate solution of the present invention may be used to passivate other types of magnetic particles. For example, the solution may be used to form passivated iron particles.

The patents set forth in the specification are intended to be incorporated by reference herein.

It is apparent that there has been provided in accordance with this invention techniques for preparing ferromagnetic particles having utility in recording media which fully satisfy the objects, means, and advantages set forth hereinbefore. While the invention has been described in combination with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoinc description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.