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

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 (Co₂MnGa, Co₂MnSi, and Co₂Fe0.4Mn0.6Si). 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 Nᵥ. Photoexcitation at hν=6.050.16em0exeV gives access to the spin-polarization texture P(EB,kₓ,ky) of the bulk bands covering a (kₓ,ky) range of 60% of the Brillouin zone. We find that Co₂MnSi and Co₂Fe0.4Mn0.6Si exhibit minority band gaps of 0.5 and 0.35 eV, i.e., decreasing band gap with increasing NV in contrast to the rigid-band expectation. For Co₂MnGa, the minority valence state maximum lies at approx. 0.2 eV above EF.