The Bell System Technical Journal 



July, 1929 



Magnetic Alloys of Iron, Nickel, and Cobalt ^ 



By G. W. ELMEN 



Synopsis: Recent investigations of magnetic properties of alloys of iron, 

 nickel and cobalt have resulted in the discovery of materials of remarkable 

 magnetic properties previously unknown. In a brief review, early experi- 

 ments that led to the discovery of these materials and the magnetic 

 properties of the entire field are discussed. Those groups of alloys of out- 

 standing scientific and technical importance such as the permalloys and 

 the perminvars and special heat treatment required for development of 

 special magnetic properties are taken up in detail. A theory is suggested to 

 account for some of the magnetic characteristics, and a few of the practical 

 applications of these materials are described. 



IF the three ferromagnetic metals — iron, nickel and cobalt — are 

 melted together in various proportions, all of the resultant alloys 

 are magnetic when the materials used are reasonably pure. The 

 magnetic properties of the alloys, however, vary greatly with com- 

 position and heat treatment. Some alloys have been found to be 

 nearly non-magnetic; others have higher permeability than any 

 hitherto known magnetic material and may be magnetically saturated 

 in the earth's field. Still others are superior at high field strengths or 

 excel in constancy of permeability at low fields. 



In the Bell Telephone Laboratories we have been especially in- 

 terested in these alloys and have made a fairly complete survey of the 

 magnetic properties of the whole field of compositions of these metals. 

 In this address I wish to tell you how our interest in those alloys was 

 aroused, what our procedure was in carrying out the investigation, 

 and what some of the principal results were. I shall also refer to 

 some of the particular applications which we have made as a result 

 of our discoveries. 



I first became interested in these alloys in 1913. At that time I 

 was looking for a magnetic material which would be more suitable for 

 certain uses in the electrical communication field than the iron then 

 used. Of the large number of alloys investigated, several contained 

 principally iron and nickel. One of these was particularly interesting. 

 The composition of this alloy was approximately 70 per cent nickel 

 and 30 per cent iron; it was a commercial alloy used as a special 

 resistance material. In the hard worked condition in which it was 



1 Journal of the Franklin Institute, Vol. 207, May, 1929, pp. 583-617. 



435 

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