Anisotropy of the electrical transport properties in a Ni_2MnGa single crystal: Experiment and theory

摘要

Electrical transport properties in ferromagnetic shape memory Ni-Mn-Ga single crystal have been investigated both in experiment and theory by analyzing electrical resistivity along different crystallographic directions during heating. The experimental results show a clear first-order martensitic transformation and a large anisotropic resistivity (AR) of 23.7% at the tetragonal martensitic phase. The theoretical conductivity (σ=1/ρ), estimated using first-principles calculations combined with classical Boltzman transport theory, proves essential crystallographic anisotropic resistivity (AR=31%) in the martensitic phase and agrees well with experimental results. The AR in the martensitic phase is reveled to mainly originate from the splitting of the minority-spin Ni 3d and Ga Ap states near the Fermi level and hence reconstruction of the minority-spin Fermi surface upon martensitic transformation.