Role of T2 Term in Temperature Dependence of the Magnetization for Fe-Ni Invar Alloys

Abstract

Precise measurements of magnetizations for single crystals of FCC Fe–Ni alloys in the Invar region have been made at temperatures from 4.2 K to 300 K in external applied fields up to 16.9 kOe to a relative accuracy of 5×10 -5 . In an analysis of these observed results with iterative least-squares method, it is found that there exists a large Stoner-type contribution varying as T 2.00±0.05 besides the spin-wave one to the temperature change in magnetization and that the coefficient of the Stoner-type contribution increases rapidly with decreasing Ni concentration, showing a maximum at about 35 at%Ni, and decreases for the alloys containing less than 35 at%Ni. It becomes evident that ferromagnetism in FCC Fe–Ni alloys disappears at a critical concentration of about 31 at%Ni. An anomalous behavior of the magnetization at low temperatures is also shown.