Crystallographic, magnetic, and electronic structures of ferromagnetic shape memory alloys Ni_2XGa (X=Mn,Fe,Co) from first-principles calculations

摘要

The crystallographic, magnetic and electronic structures of the ferromagnetic shape memory alloys Ni_2XGa (X=Mn, Fe, and Co), are systematically investigated by means of the first-principles calculations within the framework of density functional theory using the VIENNA AB initio software package. The lattice parameters of both austenitic and martensitic phases in Ni_2MnGa have been calculated. The formation energies of the cubic phase of Ni_2XGa are estimated, and show a destabilization tendency if Mn atom is substituted by Fe or Co. From Ni_2MnGa to Ni_2CoGa, the down spin total density of states (DOS) at Fermi level is gradually increasing, whereas that of the up spin part remains almost unchanged. This is the main origin of the difference of the magnetic moment in these alloys. The partial DOS is dominated by the Ni and Mn 3d states in the bonding region below E_F. There are two bond types existing in Ni_2XGa: one is between neighboring Ni atoms in Ni_2MnGa; the other is between Ni and X atoms in Ni_2FeGa and Ni_2CoGa alloys.