658 BELL SYSTEM TECHNICAL JOURNAL 



The Significance of Magnetostriction in Permalloy} L. W. Mc- 

 Keehan. Magnetostriction in permalloy confirms qualitatively the 

 existence of atomic magnetostriction as previously proposed, and 

 the explanation, based thereon, for high magnetic permeability and 

 low hysteresis in these alloys. The effect of tension upon magneto- 

 striction suggests that orientation of the magnetic axes of iron and 

 nickel atoms precisely like that due to the application of magnetic 

 fields may be effected by mechanical stresses within the elastic limit. 

 Acceptance of this view makes it possible to explain the large effects 

 of tension upon magnetic hysteresis and the observed relation between 

 the changes in electrical resistance produced by tension and by 

 magnetization. The occurrence of a reversal of magnetostriction In 

 a stretched wire containing 80 per cent nickel is covered by the same 

 explanation. A connection between magnetic hysteresis and mechan- 

 ical hysteresis is suggested and the molecular field postulated by 

 Weiss is interpreted as the integrated effect of local mechanical 

 stresses. 



Magnetostriction in Permalloy} L. W. McKeehan and P. P. 

 CiOFFi. The materials studied comprised iron, nickel, and permalloys 

 containing 46, 64, 74, 78, 80, 84, and 89 per cent nickel. The method 

 permitted simultaneous measurement of magnetization and magneto- 

 striction in about 12 cm. at the middle of a 40 cm. wire, 1 mm. in dia- 

 eter, in an approximately uniform field not exceeding 40 gauss, and 

 either with or without applied tension (within the elastic limit). 



The magnetostriction was measured by a combination of a me- 

 chanical lever, an optical lever, a multiple slit and a photoelectric 

 cell. The magnifying power of this combination, as used, was about 

 2X10^ and magnetostrictive strains from 2X10^ to 3X10^ were de- 

 tected and measured without changing the sensitivity. 



The magnetostriction-magnetization curve has initial slope zero in 

 all the cases studied. When the attainable field was sufficient for 

 magnetic saturation the magnetostriction reached a limiting value. 

 In iron there is evidence for the existence of a Villari reversal in fields 

 too great to be attained in the apparatus. In nickel there is no sign 

 of such reversal. In the permalloys with more than 81 per cent Ni 

 the magnetostriction is a contraction. In the permalloys with less 

 than 81 per cent Ni the magnetostriction is an expansion. The 

 limiting values of megnetostriction, when plotted against chemical 

 composition, fall on a smooth curve. 



^Physical Review, Vol. 28, page 158, July, 1926. 

 ^Physical Review, Vol. 28, page 146, July, 1926. 



