Field Dependence of the Stoner-Type Contribution to the Magnetization of FCC Fe-Ni Alloys

Abstract

We have performed magnetization measurements on FCC Fe-Ni alloys in the Invar region in magnetic fields up to 5.27 T at temperatures between 4.2 K and 320 K. An explicit expression of the magnetization is presented as a function of magnetic field B and temperature T , consisting of the renormalized spin wave contribution and the Stoner-type contribution varying with S T 2 . The coefficient S decreases with B , which can be written as S = S 0 (1- S 1 B ). Above about 25 K the observed magnetization is well represented by the expression, while it shows an unusual behavior below 25 K.