Scattering of charge carriers by Cr impurities in magnetotransport on a Bi(1 1 1) ultra-thin film

In this investigation we tested the role of Cr impurities on the strongly spin-polarized surface states of ultra-thin epitaxially grown Bi(1 1 1) films by measuring surface magnetoconductance and the Hall effect in conjunction with low-energy electron diffraction at a low temperature (10 K). Compared with Fe and Co, investigated recently, Cr atoms turned out to have scattering cross-sections that are about a factor of three higher than the former atoms. Nevertheless, only a small electron donation (0.03 e/atom) was found for Cr. It also exhibits strong spin–orbit scattering, as judged from quantitative analysis of weak localization effects. As a result, all spin-dependent selection rules are gradually relaxed with increasing Cr concentration, so that the initially observed weak anti-localization shifts towards weak localization. The non-monotonic decrease of conductance as a function of Cr concentration, even at 10 K, indicates high diffusivity and activated adsorption into its final optimal adsorption site. (paper)