Surface resonance of thin films of the Heusler half-metal Co2MnSi probed by soft x-ray angular resolved photoemission spectroscopy

Abstract

Heusler compounds are promising materials for spintronics with adjustable electronic properties including 100% spin polarization at the Fermi energy. We investigate the electronic states of AlO x capped epitaxial thin films of the ferromagnetic half-metal Co 2 MnSi ex situ by soft x-ray angular resolved photoemission spectroscopy (SX-ARPES). Good agreement between the experimental SX-ARPES results and photoemission calculations including surface effects was obtained. In particular, we observed in line with our calculations a large photoemission intensity at the center of the Brillouin zone, which does not originate from bulk states, but from a surface resonance. This provides strong evidence for the validity of the previously proposed model based on this resonance, which was applied to explain the huge spin polarization of Co 2 MnSi observed by angular-integrating UV-photoemission spectroscopy.

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

“…We compare the results for Co2MnSi with the spin-polarized bulk DOS calculation from [29], the recent study using Synchrotron radiation at h = 37 eV [21] and the spin-integral but k-resolved experimental and theoretical study at soft-X-ray energies [47]. The calculation (dashed curve in Figure 6d) shows very good agreement with the measured spin profile, in particular concerning the 100% at EF and the deep minimum caused by minority bands K-M.…”

“…At a very low photon energy of hν = 5.9 eV a spin-resolved photoemission experiment denied half-metallic properties for the case of ex situ prepared MgO-capped Co 2 MnSi thin films [54,55]. Soft x-ray angle-resolved photoemission spectroscopy (ARPES) on sputtered Co 2 MnSi thin films with Al capping gave evidence of the surface resonance persisting at such high energies, in good agreement with photoemission calculations [25,49,50]. In both experiments it was unclear how much the capping layer altered the results.…”

“…With one exception, all spin-resolved experiments used excitation with photon energies in the vacuum ultraviolet (VUV) regime, yielding a high surface sensitivity due to the limited inelastic mean free path (IMFP) of the photoelectrons. For sputtered epitaxial Co 2 MnSi(100) thin films we measured a spin polarization of 93% at the Fermi energy (in normal emission at hν = 21.2 eV) [34], containing a strong contribution from a fully spin-polarized surface resonance close to the Fermi energy [49,50]. A high spin polarization has also been reported for Co 2 MnGa [21], whereas Ref.…”

“…The surface states right at EF observed with p-polarized light (with intensity resonant in the region of 25-45 eV) in [21] are not visible with our s-polarized light and, in addition, the probing depth is different and the matrix elements are likely to be small at 6 eV. The majority surface resonance discussed in [47] is indicated in terms of the narrow peak with almost complete polarization at EF (marked SR in (c,d)).…”

“…Using angle integrating spin-resolved in-situ VUV-photoemission spectroscopy (h= 21.2 eV) on sputtered epitaxial Co2MnSi(100) thin films, we obtained a spin polarization of 93 % at the Fermi energy [29]. Moreover, we identified a strong contribution to the photoemission spin polarization from a fully spin polarized surface resonance close to the Fermi energy in this compound [46,47]. A similar high spin polarization was observed based on MBE-grown Co2MnSi(100) samples with h= 37 eV [30].…”