MAGNETIC PROPERTIES OF PERMINVAR 



29 



the permeability is reduced, in some cases from 40 to 60 per cent. 

 With the increase in permeability its constancy disappears both for 

 the superposed condition as shown in Fig. 4, and for ordinary 

 magnetizations at low field strengths. The hysteresis losses are also 

 increased for corresponding flux densities. These changes in the 



16000 



14000 



I?000 



10000 



B 8000 



6000 



4000 



2000 



10 20 30 40 50 60 70 



H 



Fig. 5 — ^Magnetization curves for Perminvar (45% Ni — 25% Co — 30% Fe) 



magnetic properties are largely removed by demagnetization. The 

 ordinary method of demagnetization by reversals of a slowly de- 

 creasing magnetizing force has been less successful than it is with 

 iron in returning the material to its initial state. Addition of an a.c. 

 force superposed on the d.c. helps materially in restoring the original 

 magnetic properties. 



