Exploration of novel structures and related physical properties of Fe2Pt ordered alloys

Abstract

The Fe–Pt phase diagram suggests the possible existence of ordered Fe2Pt structures, however, the ordered structures of Fe2Pt and related physical properties are unclear until now. In this work, four new low-energy ferromagnetic Fe2Pt ordered structures are predicted based on the particle swarm optimization algorithm. Their structural stability is verified by the formation enthalpy, mechanical stability and lattice dynamic stability. The order of the thermodynamic stability is Cmcm > Immm > I4/mmm > P3¯m1. All four structures are dynamically (except tetragonal I4/mmm structure) and mechanically stable. The fundamental physical properties including magnetic, elastic, phonon and thermal properties are investigated in detail. Their total magnetic moments, as well as the bulk modulus are almost the same. The shear modulus and Young's modulus of Cmcm structure are close to the P3¯m1, and larger than that of other two structures. The order of the elastic anisotropy is Immm > P3¯m1 > I4/mmm > Cmcm. The orthorhombic Immm structure can be regarded as a distorted tetragonal I4/mmm structure, and the distortion effectively improves the physical properties of the I4/mmm structure. The thermal properties at finite temperatures show that the trigonal P3¯m1 structure is more suitable for high-temperature applications compared to other structures. The results of linear thermal expansion coefficient indicate that anisotropy order of thermal expansion is Immm > I4/mmm > Cmcm > P3¯m1. More interesting is the discovery of the Invar effect along the y-axis direction in orthorhombic Immm structure.