Direct probing of temperature-independent bulk half-metallicity in Co2MnSi by spin-resolved hard x-ray photoemission

We have performed the bulk-sensitive spin-resolved hard x-ray photoelectron spectroscopy (HAXPES) to directly clarify the spin-dependent valence band electronic states and spin polarization of $L{2}_1$-ordered ${\mathrm{Co}}_2\mathrm{MnSi}$ as a predicted half-metal. The spin-resolved valence band HAXPES spectra clearly exhibited the difference in the majority and minority spin states in the bulk region of a 30-nm-thick ${\mathrm{Co}}_2\mathrm{MnSi}\left(001\right)$ thin film buried under a MgO(2 nm) layer at both temperatures of 21 and 300 K. As expected from the half-metallicity in ${\mathrm{Co}}_2\mathrm{MnSi}$, we found that the majority (minority) spin spectrum shows a metallic Fermi edge (a band gap), leading the high spin polarization of ∼90% at around the Fermi level at a temperature of 21 K. The spin-resolved HAXPES experiments revealed that the half-metallicity of ${\mathrm{Co}}_2\mathrm{MnSi}$ in the bulk region is independent on the temperature up to 300 K. The experiments also revealed the slight changes in the majority spin spectral shapes and the shift of the valence band maximum of the minority spin states with temperature. By comparing the experimental results with the first-principles calculations at a finite temperature obtained by the disordered local moment method, it is suggested that the slight changes in the majority and minority spin HAXPES spectra of ${\mathrm{Co}}_2\mathrm{MnSi}$ with temperature is mainly caused by the temperature-dependent Co $3d$ electronic states. It is also suggested that the conduction band minimum of the minority spin states is located sufficiently above the Fermi level at temperature up to 300 K.