Prediction of new stable phases of FePd2 crystal alloy

Abstract

The stable crystal structures of FePd2 under ambient pressure are explored using the particle swarm optimization technique. In addition to the previously reported tetragonal I4/mmm, orthorhombic Immm and trigonal P3¯m1 phases, three as-yet-unreported phases with R3¯m, Cmcm, and P4/nmm space group are uncovered. Subsequent first principles calculations reveals that all phases have negative enthalpy of formation and the enthalpy of the tetragonal I4/mmm phase is the lowest. Also, these phases are mechanically and dynamically stable. Their ferromagnetism and metal ductility are confirmed by the electronic structure and Pugh's ratio. The bulk modulus of these phases are almost equal, and the I4/mmm structure has the relatively higher Young's modulus and shear modulus. The dimensionless magnetic hardness parameter demonstrated that the I4/mmm and P4/nmm structures are semihard magnets, and the other structures are permanent/hard magnetic materials, in which the Immm, Cmcm, and P3¯m1 structures are the potential candidates for ultra-high density magnetic storage. The results of the bulk modulus and thermal expansion coefficient at finite temperature show that the P3¯m1 structure as a promising high-temperature structural material.