The surface composition and spin polarization of NiMnSb epitaxial thin films

Abstract

The composition in the surface region of the Heusler alloy NiMnSb has been studied using angle-resolved X-ray photoemission spectroscopy, low-energy electron diffraction and spin-polarized inverse photoemission. The results are consistent with a generally Mn-Sb terminal layer, though the surface composition is very sensitive to preparation. The surface composition has a critical influence on the polarization near the Fermi level in spin-polarized inverse photoemission. Under some conditions, the polarization at the Fermi level for normal incidence inverse photoemission can reach values very close to 100% above background.

Surface properties of the half-and full-Heusler alloys

“…This is in agreement with previous pseudopotentials calculations that showed that the surface states at the case of the MnSb-terminated NiMnSb(001) surface are localized at the surface layer [24]. Our results are in agreement with the experiments of Ristoiu et al [21] who in the case of a MnSb well ordered (001) surface measured a high spin-polarisation.…”

“…These polarisation values are consistent with a small perpendicular magnetoresistance measured for NiMnSb in a spin-valve structure [19], a superconducting tunnel junction [4] and a tunnel magnetoresistive junction [20]. Ristoiu et al showed that during the growth of the NiMnSb thin films, Sb and then Mn atoms segregate to the surface, which is far from being perfect, thus decreasing the obtained spin-polarisation [21]. But when they removed the excess of Sb by a flash annealing, they managed to get a nearly stoichiometric ordered alloy surface being terminated by a MnSb layer, which presented a spin-polarisation of about 67±9% at room temperature [21].…”

“…Ristoiu et al showed that during the growth of the NiMnSb thin films, Sb and then Mn atoms segregate to the surface, which is far from being perfect, thus decreasing the obtained spin-polarisation [21]. But when they removed the excess of Sb by a flash annealing, they managed to get a nearly stoichiometric ordered alloy surface being terminated by a MnSb layer, which presented a spin-polarisation of about 67±9% at room temperature [21]. The temperature dependence of the spin moments for such a film was studied by Borca et al [22].…”

Antiferromagnetic dipolar ordering in[Co2MnGe∕V]Nmultilayers

“…More recent superconducting/ferromagnetic point contact measurements on a Co 2 MnSi single crystal gave a spin polarization of 55% [47]. Similarly, the degree of spin polarization determined from the analysis of spin resolved photoemission spectra was always found to be definitely below 100% [48,49].…”

Photoemission study of electronic structure of the half-metallic ferromagnetCo3Sn2S2

“…While only 50% spin polarization of the Fermi-energy electrons was measured by spin-resolved photoemission ͑PE͒, 3 a spin-resolved inverse PE study shows that the polarization at E F can approach 100%. 4 The obtained discrepancy was explained by possible segregation phenomena that may lead to considerable deviations of the surface as compared to bulk stoichiometry. [3][4][5] On the other hand, due to reduced coordination even stoichiometric surfaces may exhibit an electronic structure that is very different compared to the bulk.…”