Institute of Metals Division - Effect of Annealing in a Magnetic Field Upon Iron-Cobalt and Iron-Cobalt-Nickel Alloys prepared by Powder Metallurgy

BINARY and ternary alloys of iron, nickel and cobalt respond to annealing in a magnetic field by a characteristic change in the shape of their hysteresis 100p.l,2 An increase in retentivity and a decrease in coercive force produced by the magnetic treatment cause the hysteresis loop to approach the appearance of a rectangle. Materials with a rectangular hysteresis loop have made possible the contact-rectifier³ and have greatly improved the performance of pulse transformers4 and magnetic amplifiers." In the best material presently available for these applications, a 50 pct nickel-iron alloy," the desired characteristics are achieved by aligning the preferred crystallographic directions of magnetization along the rolling direction of the tape. The objective of the present study has been to produce rectangular hysteresis characteristics in materials with inherently high saturation. Iron-cobalt alloys, exhibiting saturation values up to 24,000 gausses' appeared to offer promise for the magnetic annealing technique, because they remain magnetic to very high temperatures,8 exhibit favorable magnetostriction properties: and show zero crystal energy at 42 pct cobalt.10 Among the ternary iron-cobalt-nickel alloys,7,11 response to heat treatment in a magnetic field is unfortunately limited to alloys having rather low saturation values.' It appeared interesting nevertheless, to study a series of compositions connecting the optimum composition (50/50) of the binary iron-cobalt system with the "Perminvar" composition (30 pct Fe, 25 pct Co, and 45 pct Ni). Very recently, R. Smoluchowski and R. W. Turner," have shown that under certain circumstances magnetic annealing can produce oriented recrystallization. A combination of this technique with the domain orientation utilized in the present study might well result in further improvements. The advantages of the powder metallurgy technique in preparing magnetic alloys for study have