336 



BELL SYSTEM TECHNICAL JOURNAL 



Magnetostriction in single crystals has some very curious features. 

 A crystal of iron unites in itself all the three modes of magnetostriction 

 which have been supposed typical of iron, nickel and Heusler alloys 

 respectively. A rod having a tetragonal axis along its length expands 

 continually when exposed to a longitudinal magnetic field; a rod 

 cut along the trigonal axis contracts continually; if cut along the 

 digonal axis it first expands, then returns to its original length, finally 

 contracts. The expansion in the first of these cases may attain 

 twenty parts in a million — four or five times as great a value as one 

 ever finds with a polycrystalline sample. This shows how great the 

 extent to which the little crystals in an ordinary block of iron must 

 interfere with one another when the block is magnetized. 



Dependence of Magnetization on Temperature 

 As the temperature of a sample of iron is raised, its normal magneti- 

 zation-curve varies in a manner suggesting the influence of tension ; 



15 000 



12 500 



10 000 



13t 



u J 



7 500 



5000 



2500 



SWEDISH TPANSFORMFR 

 IRON ANNEALED AT II50°C 



1000°C 



Fig. 8 — Magnetization-vs. -temperature curves for Swedish transformer iron at three 

 values of magnetizing field. (After D. K. Morris.) 



