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BELL SYSTEM TECHNICAL JOURNAL 



by all ferromagnetic bodies and known collectively as "magneto- 

 striction." Figure 15 shows the data for change in length of rods of 

 nickel, iron, and two alloys, plotted against the field H on the one hand 

 and against relative B-H on the other. When saturation of mag- 

 netization is reached, the limiting value of magnetostriction, called 

 "saturation magnetostriction," also is attained. Its values for some 



50 100 150 200 250 300 

 H 



V2 



2/3 



(B-H)sAT. 



Fig. 15 — Magnetostriction in iron, nickel, and two iron-nickel alloys (permalloys). 



iron-nickel alloys are shown in Fig. 16. Note here that the change in 

 length is an extension in the alloys containing less than 81 per cent 

 nickel, a contraction otherwise. There is a close relation between 

 magnetostriction and the effect of strain on magnetization, it being a 

 general rule that when the magnetostriction is positive (increase in 

 length with magnetization) the effect of tension is to increase mag- 

 netization, and vice versa (Figs. 14, 15, and 16). 



How much can theory say of magnetostriction and the effect of 

 strain on magnetic properties? Figure 17 shows how the atoms are 

 arranged in an iron crystal ; each atom here is supposed to have a 



