Wannier-based description of orbital magnetic effects in ferromagnets

Abstract

I will discuss the use of Wannier functions (WFs) to calculate two basic quantities in spin-orbitcoupled ferromagnets: the anomalous Hall conductivity (AHC) and the spontaneous orbital magnetization. Both can be expressed as integrals over the Fermi sea: of the Berry curvature for the former, and of a related, but more complex object, for latter. These quantities display strong and rapid variations in k-space, demanding very dense integration meshes. By working in the representation of WFs spanning the valence and low-lying conduction bands, it becomes possible to evaluate quickly and accurately the required quantities across the BZ, in the spirit of Slater-Koster interpolation. This >Wannier interpolation> scheme circumvents the need to treat the integration mesh directly from first-principles, with considerable savings in computer time (the WFs themselves can be generated from an ab initio calculation on a relatively coarse k-point mesh). Results will be presented for the transition metals Fe, Co, and Ni, and for the ordered ferromagnetic alloys FePt and FePd.