Probing the possibility of coexistence of martensite transition and half-metallicity in Ni and Co-based full-Heusler alloys: Anab initiocalculation

Abstract

Using first-principles calculations based on density functional theory, we have studied the mechanical, electronic, and magnetic properties of Heusler alloys, namely, Ni2BC and Co2BC (B = Sc, Ti, V, Cr and Mn as well as Y, Zr, Nb, Mo and Tc; C = Ga and Sn). On the basis of electronic structure (density of states) and mechanical properties (tetragonal shear constant), as well as magnetic interactions (Heisenberg exchange coupling parameters), we probe the properties of these materials in detail. We calculate the formation energy of these alloys in the (face-centered) cubic austenite structure to probe the stability of all these materials. From the energetic point of view, we have studied the possibility of the electronically stable alloys having a tetragonal phase lower in energy compared to the respective cubic phase. A large number of the magnetic alloys is found to have the cubic phase as their ground state. On the other hand, for another class of alloys, the tetragonal phase has been found to have lower energy compared to the cubic phase. Further, we find that the values of tetragonal shear constant show a consistent trend : a high positive value for materials not prone to tetragonal transition and low or negative for others. In the literature, materials, which have been seen to undergo the martensite transition, are found to be metallic in nature. We probe here if there is any Heusler alloy which has a tendency to undergo a tetragonal transition and at the same time possesses a high spin polarization at the Fermi level. From our study, it is found that out of the four materials, which exhibit a martensite phase as their ground state, three of these, namely, Ni2MnGa, Ni2MoGa and Co2NbSn have a metallic nature; on the contrary, Co2MoGa exhibits a high spin polarization.

Ab initio study of effect of Co substitution on the magnetic properties of Ni and Pt-based Heusler alloys

“…For this set of materials, namely Co 2 MnGa, Co 2 MnSn, Co 2 FeGa, the cubic phase is the lowest energy state (c/a = 1) and they are not likely to undergo martensite transition. 13,14,29 In the lower panel of the Figure-2 we observe that for all the materials shown here (i.e. Ni 2 MnGa, Ni 2 FeGa, Pt 2 MnGa, Pt 2 MnSn), energy of the systems is lowered under tetragonal distortion which indicates to a possibility of martensite transition for these materials.…”

“…Some results of these figures are part of published literature. 14,15 of moment due to Ni substitution by Co-atom, which is always positive and proportional to the substitution and effectively results in a linear increase of the total moments of this system.…”

“…It has been observed that both T M and T C values are very much dependent on the composition of a particular Heusler alloy. [4][5][6][7][8][9][10][11][12][13][14][15][16] There is also another category of full Heusler alloys, which are known to be metallic for one kind of spin channel and insulator for the other kind of spin channel because of their very high spin polarization (HSP) at the Fermi level. They are often called as half metallic Heusler alloys.…”

Possible Martensitic Transformation in In2(Mo,W)X (X = Cr, Mn, Fe, Co, and Ni) Heusler Alloys

“…First-principles calculations have been widely used to study the physical properties of various compounds including the Heusler alloys, perovskite oxide, yttrium orthoaluminate, rhodium silicides, and carbon dioxide [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. To probe the cubic structural ground state and martensitic transition of In 2 (Mo,W)X (X = Cr, Mn, Fe, Co, and Ni) alloys, we carry out first-principles density-functional calculations with CASTEP code where the plane-wave basis set is implemented [27,28].…”

“…For instance, Mn 2 NiGa is reported to be an interesting MSMA because of a high magnetic transition temperature and a 4% magnetic-fieldinduced strain [11,12]. Co 2 MoGa displays both shape memory effect and large spin polarization at the Fermi level [13]. * corresponding author; e-mail: x-yang@cauc.edu.cn…”