MAGNETIC MATERIALS IN RELATION TO STRUCTURE 27 



Ileusler Alloys 



One of the most interesting groups of magnetic materials comprises 

 the Heusler alloys "^^ which are ferromagnetic although composed of 

 non-ferromagnetic elements. A representative alloy of this type is one 

 containing copper, manganese, and aluminum. The magnetic prop- 

 erties are associated with the composition Cu2MnAl, since the magnetic 

 intensity of the alloys varies in proportion to the amount of this phase. 

 These properties also depend upon structure.^" The ferromagnetic 

 condition is obtained by quenching the alloy from approximately 

 800° C. This treatment produces a body centered cubic structure 

 with a face centered superlattice. Manganese is essential to the com- 

 position; copper may be replaced by silver; ^® aluminum by other triva- 

 lent or tetravalent elements — for example, tin. 



Although possessing no properties of commercial utility, the alloys 

 are extremely important in relation to magnetic theory. For those 

 who may be particularly interested, a rather complete list "^^ of recent 

 papers on the subject is given in the references. 



Summary of Magnetic Characteristics of Sheet Materials 



There are now available for magnetic purposes a large number of 

 materials which are suitable for use over different ranges of magnetizing 

 force and at different flux densities. In summarizing properties, the 

 materials are grouped according to their adaptability at different 

 magnetizing forces. 



For low forces, where very high permeabilities are required, as in 

 some signal apparatus, 78-permalloy is a suitable material. Molyb- 

 denum or chromium permalloy has properties similar to those of 

 78-permalloy but has higher initial permeability, is more readily heat- 

 treated and is to be preferred for alternating current applications be- 

 cause of the higher resistivity. Hydrogen-treated iron at low mag- 

 netizing forces also has properties similar to those of the 78-permalloy. 



For small magnetizing forces where a constant permeability and very 

 low hysteresis loss is required, the heat-treated perminvars are avail- 

 able. The flux densities in cores of this type, if constant permeability 

 and low hysteresis loss are retained, must be kept below 1000 gauss. 



For apparatus using higher magnetizing forces, iron-nickel alloys in 

 the range of 40 to 55 per cent nickel, and the silicon steels are most 

 suitable. These two materials are widely used in electric transformers. 



In the region of fields of 10 to 50 oersteds and higher, the 50-50 

 iron-cobalt and vanadium-modified alloy are attractive because of the 

 high intrinsic induction of approximately 22,000 gauss. This superi- 

 ority exists even in fields of over 1000 oersteds, but in the higher 



