30 



BELL SYSTEM TECHNICAL JOURNAL 



Hard Magnetic Materials (Permanent Magnets) 



Permanent magnet materials, as pointed out in the introduction to 

 this paper, are characterized by properties different from those of the 

 soft magnetic alloys. With these materials, a high residual induction 

 and high coercive force are required. Permanent magnets in use 



150 



!2 125 



•- -• 5% Al, 25^ Ni 



-• 12.5% Al, 21% N 



900 



Fig. 



200 300 400 500 600 700 800 



AGING TEMPERATURE IN DEGREES CENTIGRADE 



14 — Effect of aging treatment on typical iron-nickcl-aluniinuni magnet alloys- 



Koster^^ 



commercially at this time are steels. High intrinsic induction is as- 

 sured by a high proportion of iron in the composition; the magnetic 

 hardness is assured by the addition of carbon, which, when the steel is 

 suitably heat-treated, precipitates as a finely dispersed carbide 

 throughout the matrix. This finely dispersed precipitate keys the 



