Induced Magnetic Moment in Ferromagnetic Fe Alloys by Tetragonally Elongated Lattice Expansion

Abstract

Magnetization and Mössbauer spectra were measured for Fe–C, Fe–N and Fe–Ni–C systems. The mass ratio of the tetragonal martensite in the mixed phases was determined by means of Mössbauer spectroscopy, leading to the average magnetic moment of Fe atoms in the body centered tetragonal (bct) structure.
The magnetic moment of Fe atoms increases from 2.2 μ_B to 2.6 μ_B as the axial ratio and the volume of unit cell increase. In other words, the volume expansion and/or the tetragonal elongation seem to cause an increase in the magnetic moment of Fe in bct alloys. It is concluded that the variation of the magnetic moment of Fe in the bct structure can be explained as a superposing effect of both volume expansion and tetragonal expansion.
The mechanism of these effects is discussed in terms of energy band splitting of d electrons and magnetovolume effects.