Alloying and magnetic disordering effects on the martensitic transformation and elastic property of Co2VGa Heusler alloy: A first-principles study

Using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, the alloying and magnetic disordering effects on the phase stability and elastic property of L21- and D022-Co2VGa Heusler alloy are systematically investigated. It is shown that at the ground ferromagnetic (FM) state, Co2VGa alloy possesses the L21 structure and correspondingly, its shear modulus, Young modulus, and Debye temperature of the phase are all larger than those of the D022 phase. When the FM state transiting to the paramagnetic (PM) one, both C '(= (C11 -C12)/2) and C44 of the L21 phase decrease whereas the elastic anisotropy increases, and they do so as well with increasing the number of valence electrons per atom (e/a) in the off-stoichiometric ternary and doped quarternary alloys with the FM ordering. As a result, at 0 K the magnetic disordered Co2VGa alloy with the disordering degree (y) larger than 0.2 can show the martensitic transformation (MT) from L21 to D022, and the MT is also obtained in the FM Co2V(Ga1,Zx) alloys with Z = Co (x > 0.2), V and Ge (x > 0.4), Si (x > 0.5), and Sb (x > 0.3). Accompanying the MT, their volume tends to decrease, and these L21 alloys possessing a bigger volume than those with the same e/a ratios are also relatively more prone to the MT. In the Z = V alloys, both greater magnetocaloric and magnetostrain effects may be expected during the MT as well. Both the minority Co d and V d states around the Fermi level should be responsible for the composition and magnetic ordering dependence of the phase stability of Co2VGa alloy.