Permalloy, A New Magnetic Material of 

 Very High Permeability 



By H. D. ARNOLD and G. W. ELMEN 



Synopsis: The magnetic alloy described in this paper is a composition 

 of about 78.5% nickel and 21.5% iron and at magnetizing fields in the 

 neighborhood of .04 gauss and with proper treatment has a permeability 

 running as high as 90,000. This is about 200 times as great as the permea- 

 bility of the best iron for these low magnetizing fields. This high permeabil- 

 ity is attendant upon proper heat treatment and also upon other factors 

 among which is freedom from elastic strain. The presence of other elements 

 than iron or nickel and specially carbon, reduces the permeability, but 

 slight variations in heat treatment produce large changes compared with 

 those due to small quantities of impurities. 



So far as discovered, other physical properties show no peculiarities at 

 the composition which brings out the remarkable magnetic properties of 

 permalloy. The equilibrium diagram, electric conductivity, crystal struc- 

 ture, mean spacing between adjacent atom centers and density are among 

 the physical properties which have been studied. 



To the engineer in electrical communication the development of perm- 

 alloy is very significant. It assures a revolutionary change in submarine 

 cable construction and operation and promises equally important advances 

 in other fields. — Editor. 



SOME time ago it was discovered in the Bell System laboratory 1 

 that certain nickel-iron alloys, when properly heat-treated, 

 possess remarkable magnetic properties. These properties are devel- 

 oped in alloys which contain more than 30 per cent of nickel and 

 which have the face-centered cubic arrangement characteristic of 

 nickel crystals, rather than the body-centered structure characteristic 

 of iron. The entire range above 30 per cent nickel exhibits these 

 properties to some degree and offers new possibilities to those inter- 

 ested in magnetic materials. The most startling results, however, 

 are obtained with alloys of approximately 80 per cent nickel and 20 

 per cent iron, whose permeabilities at small field strengths are many 

 times greater than any hitherto known. To alloys of this approximate 

 composition we have given the name "permalloy". The development 

 of permalloy has assured us a revolutionary change in submarine 

 cable construction and operation, and promises equally important 

 advances in other fields of usefulness. It also presents questions of 

 great interest to the scientist, and emphasizes again the meagreness 

 of our fundamental information about ferromagnetism. The present 

 paper is intended to give a general discussion of the preparation and 

 testing of permalloy, with sufficient detail to indicate its unusual 

 characteristics. Detailed statements of numerical results are reserved 

 for publication in separate articles dealing with specific properties. 2 



'British Patent No. 188,688. 



2 L. W. McKeehan, The Crvstal Structure of Iron-Nickel Alloys, Phys. Rev. (2), 

 21, (1923). 



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