254 



BELL SYSTEM TECHNICAL JOURNAL 



tion. Microphotographs of a single-phase alloy and a two-phase alloy of 

 iron-cobalt-molybdenum are reproduced in Fig. 3 (a) and (b). 



The diagram of Fig. 2 shows several kinds of changes that afifect the mag- 

 netic properties. At (a) the material becomes non-magnetic on heating, 

 without change in phase. At (b) there is a change of phase, both phases 



;^ 400 



(J 



2 100 



200 400 600 800 1000 



TEMPERATURE IN DEGREES CENTIGRADE 



Fig. 4 — Effect of phase transformation of cobalt on magnetization with a constant 

 field of 150 oersteds. Both phases magnetic. Masunioto. 



5 16 



200 400 600 800 1000 1200 



TEMPERATURE IN DEGREES CENTIGRADE 



Fig. 5 — Phase transformation in iron-cobalt alloy (50% Co). High-temperature phase 

 is non -magnetic. 



being magnetic. Figure 4 shows the changes in magnetic properties that 

 occur during this latter transition; they are due partly to the high local 

 strains that result from the change in structure, and partly to the difference 

 in the crystal structures of the two phases. At (c) there is a change from a 

 ferromagnetic to a non-magnetic phase, and Fig. 5 shows the rapid change 

 in magnetization that occurs when the temperature rises in this area. At 



