Large anisotropy of spin polarization in Heusler alloy Ni2MnGa induced by martensitic transformation

Spin polarization both in the cubic austenitic and tetragonal martensitic phases of the Ni(2)MnGa alloy has been investigated using first-principles calculations combined with classical Bloch-Boltzmann transport theory. It is shown that the degree of spin polarization, while decreasing from 42% in the < 001 > directions of the austenitic phase to 30% in the [100] direction of the martensitic phase, rises to 75% in the [001] direction of the martensitic phase, resulting from a preferential reconstruction of the spin-down Fermi surfaces upon martensitic transformation. With this finding, various recent intriguing electrical measurements upon Ni(2)MnGa across the martensitic transformation can find an explanation. This also opens a way of searching for giant magnetoresistance materials. (C) 2008 American Institute of Physics.