38 BELL SYSTEM TECHNICAL JOURNAL 



permeability and fair constancy makes for a larger range of flux 

 densities in which the permeability is constant and consequently also 

 increases the range of flux densities with low hysteresis loss. 



Experiments on several alloys of this series indicated that by 

 baking the alloys at 425° C. the area enclosed by the curve in Fig. 8 

 would be increased considerably, and possibly would include some of 

 the binaries of these metals. 



Discussion 



While this paper is concerned primarily with the study of the 

 magnetic properties of these alloys and the dependence of these 

 properties on composition and on heat treatment, some of the results 

 are of considerable theoretical interest, as they suggest the manner in 

 which the unusual magnetic properties are acquired by the alloys. 

 It was shown in the heat treating experiments that the unusual 

 magnetic properties resulted from suitable heat treatment of certain 

 compositions. Slow cooling through a rather narrow temperature 

 range, or continuous heating for a long time at the lower end of this 

 range resulted in alloys which had marked perminvar characteristics. 

 Rapid cooling through this temperature range usually did not develop 

 these characteristics. From the measurements at elevated tempera- 

 tures, Fig. 8, it was shown that in the temperature range from 400° C. 

 to 500° C, the change in the alloys is quite rapid at the higher tempera- 

 ture, but that the rate of stabilization slows up as the temperature 

 decreases. When the alloy is heated and cooled through a tempera- 

 ture cycle in this manner, the permeability changes progressively and 

 at each temperature in the cycle the alloy reaches a stable condition 

 if the rate of cooling or heating is slow enough. There is a striking 

 similarity in the manner in which these changes in permeability are 

 developed, and in the progress of the constitutional changes in an 

 alloy which at high temperatures is a homogeneous solid solution, 

 but as the temperature falls becomes saturated and segregates into a 

 mixture of two solid solutions of different concentration. 



That such a segregation takes place in the slowly cooled alloys is 

 also supported by a study of the differences in the shapes of the 

 hysteresis loops of the quenched and the slowly cooled alloys. Ordi- 

 narily, the widest part of a hysteresis loop of a homogeneous material 

 is the intercept on the H axis. All the loops of the air-quenched 

 alloys have these characteristics. Gumlich ^ has shown that if a 

 magnetic circuit is made of two materials of different magnetic 

 properties, the loops may assume a variety of shapes, ranging from 



^E. Gumlich, Arch. f. Elektrotechnik , Vol. 9, p. 153, 1920. 



I 



