. The Bell System technical journal . fore it was air quenched. This change is inaccordance with what would be expected if a segregation took placewith annealing. A homogeneous solid solution has the highestresistivity and segregation tends to lower it. MAGNETIC ALLOYS OF IRON, NICKEL, AND COBALT 459 Other interesting evidence is obtained from the study of thehysteresis loops. For the perminvar alloys the constricted loops arevery marked and easily produced. In the permalloys containingbetween 60 and 80 per cent nickel also there is a tendency to con-striction in the slowly cooled alloy, not s
. The Bell System technical journal . fore it was air quenched. This change is inaccordance with what would be expected if a segregation took placewith annealing. A homogeneous solid solution has the highestresistivity and segregation tends to lower it. MAGNETIC ALLOYS OF IRON, NICKEL, AND COBALT 459 Other interesting evidence is obtained from the study of thehysteresis loops. For the perminvar alloys the constricted loops arevery marked and easily produced. In the permalloys containingbetween 60 and 80 per cent nickel also there is a tendency to con-striction in the slowly cooled alloy, not so marked but sufficiently^prominent to lead me to believe that the same general changes occurin both groups of alloys, differing only in the nature of the segregatesand the ease with which segregation occurs. Now we know that homo-geneous magnetic materials have a characteristic type of hysteresisloop. For such materials there is no constriction in the middle, butthe widest part of the loop is generally at that point. We also can r r. Fig. 19—Hysteresis loops: a, perminvar (45 per cent Ni, 25 per cent Co, 30 per centFe); h, bi-metallic rod. Loop traced with cathode ray oscillograph. construct hysteresis loops which have constrictions by making upcores of several materials in a parallel or parallel-series arrangement.^This is illustrated by the hysteresis loop h in Fig. 19. This loop istraced by a cathode ray oscillograph for a bi-metallic rod, 15 in. longconsisting of a core of .04 in. diameter unannealed piano wire and in. wall permalloy tube, heat treated to give high permeabilityand fitting closely to the wire. Curve a is a loop similarly traced fora perminvar core. Though the magnetic circuit conditions for thetwo cores are not the same, the marked similarity of the two loopsfavors the view that the constricted loop of the perminvar resultsfrom segregation. It is interesting to note in this connection that the examination byX-ray crystal analysis methods of these al
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