Abstracts of Technical Articles from Bell System Sources 



Heat Treatment of Magnetic Materials in a Magnetic Field — //. 

 Experiments with Two Alloys.^ Richard M. Bozorth and Joy F. 

 DiLLiNGER. The magnetization of two alloys, as affected by heat 

 treatment in a magnetic field at various temperatures, is examined in 

 some detail in order to elucidate the nature of the accompanying 

 changes which result in some cases in a 30-fold increase in maximum 

 permeability. The experiments show that these alloys (one con- 

 taining approximately 35 per cent iron and 65 per cent nickel, the 

 other 20 per cent iron, 60 per cent cobalt and 20 per cent nickel) can 

 be effectively heat treated in a magnetic field of 10 oersteds if the 

 temperature is above 400° C. and below the Curie point of the alloy. 

 The time during which the magnetic properties change has been 

 measured at different temperatures and is found to vary according to 

 the equation r = A^"''^. The experiments are interpreted in terms of 

 the domain theory of ferromagnetism. The changes which occur are 

 due to the relief of magnetostrictive stresses which arise when the 

 material becomes ferromagnetic upon cooling through the Curie 

 point or when an external magnetic field is applied, and the relief 

 comes about by plastic flow or diffusion in the separate domains. The 

 values of A (about 10~^^ second) and W (2.1 electron volts) are the 

 same as those determined by Bragg and Williams for the above equa- 

 tion which also gives the time necessary for the establishment of a 

 superstructure in alloys. The relation between the two processes, 

 establishment of superstructure and the relief of magnetostrictive 

 strains, is pointed out. | 



Heat Treatment of Magnetic Materials in a Magnetic Field — I. 

 Survey of Iro7t- Cobalt-Nickel Alloys."^ Joy F. Dillinger and Richard 

 M. Bozorth. The changes that occur in the magnetic properties of 

 iron-cobalt-nickel alloys when they are annealed in a magnetic field, 

 have been investigated for a series of these alloys. The maximum 

 change for the iron-nickel alloys occurs between 65 and 70 per cent 

 nickel and is evidenced by a large increase in maximum permeability 

 and a hysteresis loop of rectangular shape. All of the alloys with 

 Curie points above 500° C. and with no phase transformation have 

 their properties similarly changed. Thorough preliminary annealing 



• Physics, September, 1935. 



* Physics, September, 1935. 



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