Electrical and magnetic properties of nanocrystalline Fe 100−xNi x alloys

Abstract

The electrical and magnetic properties of nanocrystalline binary Fe 100− x Ni x alloys, where x ranges from 0 to 100, prepared by a combination of aqueous and solid-state reduction processes have been studied vis-à-vis their microstructure. The microstructural studies indicate the formation of near-equilibrium phases in the alloys with crystallite size in the range 20–40 nm. The crystallite size in the case of pure Fe and Ni, however, is in the range 40–80 nm. The electrical transport in the temperature range 20–300 K exhibits a typical ferromagnetic metallic behavior in all the cases and the absolute resistivity of nanocrystalline Fe 100− x Ni x alloys decreases monotonically with increasing Ni content. The saturation magnetization of the alloys on the other hand decreases progressively with Ni addition towards that of pure Ni value. The coercivity of alloys is found to be independent of temperature in the range 5–300 K except in the case of pure Ni wherein it increases from 30 Oe at 300 K to 65 Oe at 5 K. The electrical and magnetic properties of the nanocrystaline Fe–Ni alloys do not follow the predictions of simple itinerant band model for alloys. The temperature dependence of saturation magnetization in all the cases has a T 3/2 Bloch variation while the average atomic moment of the alloys has an effective medium composition dependence.