38 



BELL SYSTEM TECHNICAL JOURNAL 



Oxide Magnets 

 In this class of materials are included the metallic oxide magnets 

 recently described in the literature by Kato and Tokei.''^ The metallic 

 oxide magnets, open a new field of permanent magnet materials. 



. ■ tv • 



Fig. 19 — Typical structure of an age-hardening iron-cobalt-moiybdenuin alloy, 

 containing 12 per cent cobalt and 16 per cent molybdenum, after quenching from 

 1.300° C. Mag. 125 X. 



These magnets are composed, according to the Japanese authors, in 

 one instance of a solid solution of cobalt ferrite (CoFe204) in magnetic 

 iron oxide (FeFe204). Although the method of manufacture and exact 

 compositions are not completely disclosed, it appears that the prepara- 

 tion involves the powdering of the metallic oxides, compressing in a 

 suitable die to the desired shape, and subsequent heating. 



Cobalt ferrite magnets, it is reported, are not easily magnetized at 

 room temperature; but if the temperature is raised, for example, to 



