Crystal structure and site preference, magnetic and elastic properties, and martensitic transformation of Ni- and Fe-doped Co2VGa alloys: A first-principles study

Abstract

Using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, the crystal structure and site preference, magnetic and elastic properties, and martensitic transformation (MT) are systematically investigated with the three groups of Heusler alloys: (Co[Formula: see text]M[Formula: see text])VGa (M1[Formula: see text]), Co[Formula: see text](V[Formula: see text]M[Formula: see text])Ga (M2[Formula: see text]), and Co[Formula: see text]V(Ga[Formula: see text]M[Formula: see text]) (M3[Formula: see text], M = Ni and Fe, [Formula: see text]). It is shown that instead of the [Formula: see text] and [Formula: see text]A structures, the fcc one is energetically preferred in the cubic M3 x ([Formula: see text]) alloys. In [Formula: see text]-Ni2 x ([Formula: see text]) and fcc-Ni3 x ([Formula: see text]), Ni atoms even prefer the Ga and Co anti-sites, respectively, and the replaced atoms move to the sublattices of the deficient ones. Their total magnetic moment is dominated by the magnetic exchange interactions corresponding to the pairs of two Co atoms on the different sublattices in M = Ni and Fe1 x, Co and Fe in Fe2 x and Fe3 x ([Formula: see text]), and Fe and Fe atoms in Fe3 x ([Formula: see text]) alloys, respectively. These Ni1 x, Ni2 x, and Fe3 x with [Formula: see text] as well as Ni3 x with [Formula: see text] alloys are predicted having the MT behavior and also the better mechanical property relative to Co[Formula: see text]VGa. A lower shear modulus ([Formula: see text]) generally corresponds to a higher MT temperature, and these alloys, which can undergo the MT are further evaluated with [Formula: see text] GPa. Both considerable magnetocaloric and magnetovolume effects can be also expected during the MT of these Fe3 x alloys ([Formula: see text] and 0.6). In the remaining Fe1 x and Fe2 x alloys, the Fe doping disfavors the MT and also improves their brittleness. The structural preference of these cubic alloys and also their stability relative to the tetragonal martensite can be mainly attributed to the number of their minority density of states at the Fermi level: the smaller they are, the more stable their system tends to be.