Band structure tuning of Heusler compounds: Spin- and momentum-resolved electronic structure analysis of compounds with different band filling

Abstract

Half-metallic ferromagnetic Heusler compounds represent an important class of materials for spintronic applications. We experimentally observe the dispersion of electronic bands with spin resolution in three representative Heusler compounds (${\mathrm{Co}}_{2}\mathrm{MnGa}, {\mathrm{Co}}_{2}\mathrm{MnSi}$, and ${\mathrm{Co}}_{2}{\mathrm{Fe}}_{0.4}{\mathrm{Mn}}_{0.6}\mathrm{Si}$). Bulk-sensitive measurements at very low photon energy are complemented by spin-integrated hard x-ray angular resolved photoemission spectroscopy. The dispersion of majority and minority electrons allows us to link exchange splitting and band filling to the number of valence electrons ${N}_{v}$. Photoexcitation at $h\ensuremath{\nu}=6.05\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ gives access to the spin-polarization texture $\mathbit{P}({E}_{B},{k}_{x},{k}_{y})$ of the bulk bands covering a $({k}_{x},{k}_{y})$ range of 60% of the Brillouin zone. We find that ${\mathrm{Co}}_{2}\mathrm{MnSi}$ and ${\mathrm{Co}}_{2}{\mathrm{Fe}}_{0.4}{\mathrm{Mn}}_{0.6}\mathrm{Si}$ exhibit minority band gaps of 0.5 and 0.35 eV, i.e., decreasing band gap with increasing ${N}_{\mathrm{V}}$ in contrast to the rigid-band expectation. For ${\mathrm{Co}}_{2}\mathrm{MnGa}$, the minority valence state maximum lies at approx. 0.2 eV above ${E}_{\mathrm{F}}$.