Magnetic Moment of Iron - Nickel Invar Alloys Between 4 And 80 K

Abstract

The magnetic moment of several ferromagnetic f.c.c. iron—nickel alloys in the invar region has been investigated at low temperatures as a function of both the magnetic field and the temperature. A vibrating sample magnetometer has been constructed for these measurements with a relative sensitivity of three parts in 10(5). Such data resolution has permitted a detailed analysis of the temperature dependence of the measurements resulting from contributions at constant volume from spin wave and single particle excitations together with a term describing the effects of volume change on the magnetization. Because of the very large and negative thermal expansion of commercial invar (Meincke and Graham, 1963), this latter contribution is very significant. When the single particle and volume terms are considered in conjunction with other thermodynamic data, they suggest that the invar alloys can be interpreted on a rigid band model. Consequently, this model has been analyzed with the result that the static magnetoelastic anomalies can be understood on the basis of an approach to instability of the ferromagnetic state occasioned by the shape of the density of states.