MAGNETIC MATERIALS IN RELATION TO STRUCTURE 



25 



Heat Treatment of Magnetic Material in Magnetic Field ^^ 



Recently it has been reported that radical changes have been pro- 

 duced in the magnetic properties of some ferro-magnetic alloys by heat 

 treatment in a magnetic field. For example, the maximum perme- 

 ability of the permalloy containing 65 per cent of nickel has been in- 



Fig. 12 — Structure of an iron-nickel alloy, as cast, containing 80 per cent nickel 

 and 0.030 per cent sulphur. The sulfide constituent exists as a brittle film surround- 

 ing the crystallites. Mag. 2000 X. 



creased from 10,000 to 250,000 by heating to 700° C. and cooling 

 slowly in a field of 15 oersteds. The maximum permeability has been 

 further increased to 600,000 by so treating a specimen which had 

 previously been treated in hydrogen at 1400° C. This value of max- 

 imum permeability is the highest which has been reported for any 

 ferromagnetic material. 



