Instability of the Parent Phase in Nearly Ordered Fe3Pt Invar Alloys

Abstract

The martensitic transformation in a nearly ordered Fe3Pt is weak first order, and the martensite phase shows a large magnetic field-induced strain of several percent. We have investigated the origin of this transformation from its electronic structure. A characteristic feature in the electronic structure is the existence of a relatively high peak in the density of states of the minority spin band just below the Fermi energy. This peak splits into two peaks by tetragonal distortion, and one of them shifts to lower energy by the distortion, suggesting that the band Jahn-Teller effect is the main cause for the transformation.