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BELL SYSTEM TECHNICAL JOURNAL 



The perminvars are the next group with interesting characteristics. 

 Their remarkable constancy of permeabiHty at low magnetizing forces 

 and their extremely low hysteresis loss at low flux densities make them 

 of unusual interest. The composition 45 per cent nickel, 25 per cent 

 cobalt and 30 per cent iron is a typical alloy for this group. Perme- 

 ability curves for this alloy for three types of heat treatment are plotted 

 against magnetizing force in Fig. 11. The insert in the upper right- 

 hand corner shows the lower parts of these curves plotted to a larger 

 scale. For the baked alloy the permeability is constant at 300 with 



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H 



Fig. 11 — Permeability curves for a perminvar alloy containing 45 per cent Ni, 

 25 per cent Co, 30 per cent Fe. 



an increase of the magnetizing force from zero to 2f gauss. The 

 initial permeability for the air-quenched alloy is more than twice that 

 of the baked, but the constancy of permeability is a great deal less. 

 This illustrates the close relation of these two properties. As the 

 magnetizing force approaches 40 gauss the differences in the perme- 

 abilities, resulting from different rates of cooling, disappear. 



The hysteresis loops for this composition are also of unusual interest. 

 Fig. 12 illustrates the hysteresis characteristics for this alloy, in air- 

 quenched and baked condition, for three maximum flux densities, 750, 

 1,000 and 5,000 gauss, respectively. For the lowest flux density of 



