Ab initio Study of High-field NMR Shift of 59Co in the Ferromagnetic Heusler Alloy Co2TiGa

Abstract

The high-field NMR shift of ⁵⁹Co in the ferromagnetic state of the Heusler alloy Co₂TiGa has been calculated to be +0.65% by local density approximation (LDA) involving the spin–orbit interaction based on density functional theory (DFT) and Korringa–Kohn–Rostoker (KKR) Green’s function method. This value explains the experimental value of +0.83% semiquantitatively. The high-field NMR shift of ⁵⁹Co is shown to be related closely with the net polarizations of Co-d and Co-s spin states only at the Fermi energy ε_F. The observed positive shift is shown to be a manifestation of the half-metallic character of the band structure inherent in Co-based Heusler alloys, where the spin-resolved partial density of states of s-electrons with up spin, D_s↑(ε_F), is much larger than D_s↓(ε_F), resulting in an important positive contribution to the field-induced hyperfine field.