Lattice Dynamics and Invar Properties in f.c.c. FeMn Alloy

Abstract

Using inelastic neutron scattering the phonon dispersion relations in a single crystal of face centered cubic Fe_0.7Mn_0.3 have been determined at several temperatures above and below the Néel temperature of 412 K. The shifts of the frequencies of the [110]T₁ mode below T_N have been observed, which eventually gives the elastic softening similar to the previous observation in the typical ferromagnetic Invar of Fe_0.65Ni_0.35 or Fe_0.72Pt_0.28. Lattice dynamical features in this material are discussed with respect to the Invar characters in the f.c.c. FeMn alloys.