THE PHYSICAL BASIS OF FERROMAGNETISM 



27 



shown In Fig. 15. The maximum in the curve near 70 per cent nickel 

 apparently corresponds to the maximum of the interaction curve of 

 Fig. 14. In alloys of higher nickel content the curve indicates that 

 the Curie point should be increased if the material is compressed- The 

 opposite should be true of the face-centered alloys having less than 

 this amount of nickel. These contentions are borne out by the fact 



800 



■?; 700 



600 



O 500 



UJ 400 



300 



? 200 



10 20 30 40 50 60 70 80 90 TOO 



NICKEL IN PER CENT 



Fig. 15 — The Curie temperatures for iron-nickel alloys, showing a maximum 

 corresponding to the maximum of Bethe's curve of Fig. 14. 



that under a hydrostatic pressure of 10,000 atmospheres the 30 per cent 

 nickel alloy becomes practically non-ferromagnetic ^^ at room tempera- 

 ture (permeability is independent of field-strength and equal to 1.7). 

 On the other hand the effect of the pressure on the phase equilibrium is 

 unknown so that the data might be explained also by a change of phase 

 '« R. L. Steinberger, Physics, 4, 153-161 (1933). 



