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BELL SYSTEM TECHNICAL JOURNAL 



loops is the absence of coercivity. For loops having maximum flux 

 densities of 5,000 or less the ascending and descending branches pass 

 through the origin. For greater flux densities the coercivity begins 

 to be measurable, but there is still a considerable constriction of the 

 loop for a maximum flux density of 8,000 gauss. It is only in the loop 

 for 15,000 gauss, that the constriction at the origin has disappeared 

 and the loop resembles those for ordinary magnetic materials. In 

 Table I the hysteresis losses for the complete loops are tabulated. 



Fig. 4 illustrates graphically how the permeability measured with a 

 constant alternating current magnetizing force of about .0021 gauss 

 and 200 cycles per second is affected when a steady magnetizing force 



25 20 15 10 



4 2 2 4 



DC. MAGNETIZING FORCE 



10 15 20 25 



Fig. 4 — The effect of superposed d.c. fields on the a.c. permeability of Perminvars 



(45% Ni— 25% Co— 30% Fe) 



is superposed on the magnetic circuit, the steady force being produced 

 by a direct current. The arrows in the figure indicate the direction 

 in the progress of the permeability as the direct current magnetizing 

 force is varied. The permeability is substantially constant as the 

 direct current magnetizing force increases up to approximately 1.7 

 gauss and it then suddenly rises as the force is increased beyond that 

 value. This is the same field strength at which the permeability 

 begins to increase as shown in Fig. 1. 



Another characteristic of this material not found in ordinary 

 magnetic substances also is shown in Fig. 4. After an applied d.c. 

 magnetizing force of 25 gauss is removed, the permeability has risen 

 from 460 to 750. With ordinary materials, after such magnetization, 



