MAGNETIC MATERIALS IN RELATION TO STRUCTURE 



21 



The permalloys in the region of 75 per cent nickel have been further 

 modified by the addition of third elements ''' which are non-ferro- 

 magnetic. Molybdenum and chromium are elements of this nature 

 which confer on the alloys certain characteristics of sufficient interest 

 to warrant discussion. The effects of molybdenum and chromium on 

 the magnetic quality are shown in Fig. 9, which indicates that higher 

 initial permeabilities may be expected with the ternary alloys. The 

 addition of a third element increases the electrical resistivity of the 

 alloy. This is of importance in alternating current applications where 

 eddy current losses are a consideration. In commercial manufacture 

 the third element is particularly valuable, since it decreases the sensi- 



120,000 



100,000 



20.000 



1000 2000 3000 4000 5000 6000 

 B IN GAUSS 



7000 8000 9000 10.000 



Fig. 9 — Permeability curves obtained for laboratories' samples comparing the 

 properties of chromium permallo}' and molybdenum permalloy with those of standard 

 permalloy — Elmen i^. 



tivity of the magnetic properties of the alloy to the rate of cooling after 

 annealing and, in fact, permits the attaining of high permeabilities with 

 slow cooling. The significance of this from a structural viewpoint is 

 that the third element keeps the iron and nickel atoms in a disordered 

 distribution. 



Iron-nickel alloys have a limited field of application in the form of 

 thin tape in the hard rolled condition. A representative material is 

 one containing from 30 to 70 per cent nickel and, in addition, a few per 

 cent of aluminum or copper, which in the hard rolled condition has been 

 called "isoperm."^^ The material is reported to have a low perme- 

 ability of 50 to 75, which is fairly constant over a range of magnetizing 

 forces of 0-10 oersteds. Laminated cores of this material have prop- 



