Surface spin polarization of the nonstoichiometric Heusler alloy Co2MnSi

Using a combined approach of spin-resolved photoemission spectroscopy, band structure and photoemission calculations we investigate the influence of bulk defects and surface states on the spin polarization of nonstoichiometric Co2Mn alpha Si thin films (with alpha = 0.69 and alpha = 1.19) with bulk L2(1) order. We find that for Mn-poor alloys the spin polarization at the Fermi energy (E-F) is negative due to the presence of Co-Mn antisite and minority surface state contributions. In Mn-rich alloys, the suppression of Co-Mn antisites leads to a positive spin polarization at E-F, and the influence of minority surface states on the photoelectron spin polarization is reduced.