Spin- and time-resolved photoemission studies of thin Co2FeSi Heusler alloy films

TL;DR

This study investigates the spin polarization of Co2FeSi Heusler alloy films using spin- and time-resolved photoemission spectroscopy, revealing depth-dependent effects and mechanisms affecting surface spin polarization.

Contribution

It provides new insights into the spin-dependent lifetime effects and the depth profile of spin polarization in Co2FeSi films using advanced photoemission techniques.

Findings

Differences in spin polarization depend on photoemission mechanism.

Spin-dependent lifetime effects influence observed polarization.

Reduction in spin polarization occurs at depths of 4-6 nm from the surface.

Abstract

We have studied the possibly half metallic Co2FeSi full Heusler alloy by means of spin- and time-resolved photoemission spectroscopy. For excitation, the second and fourth harmonic of femtosecond Ti:sapphire lasers were used, with photon energies of 3.1 eV and 5.9 eV, respectively. We compare the dependence of the measured surface spin polarization on the particular photoemission mechanism, i.e. 1-photon-photoemission (1PPE) or 2-photon photoemission (2PPE). The observed differences in the spin polarization can be explained by a spin-dependent lifetime effect occurring in the 2-photon absorption process. The difference in escape depth of the two methods in this context suggests that the observed reduction of spin polarization (compared to the bulk) cannot be attributed just to the outermost surface layer but takes place at least 4-6 nm away from the surface.