Thickness-dependent electronic and magnetic states of Mn and Co atoms at Mn-rich Co2Mn1.20Ge0.38/MgO interfaces via soft x-ray magnetic circular dichroism

The magnetic states of Mn and Co atoms in Mn-rich and Ge-deficient Co2Mn1.20Ge0.38 (CMG) Heusler alloy thin films facing an MgO barrier were studied by means of x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD). In particular, the CMG film-thickness dependence of the Mn and Co magnetic moments was investigated. A Co2+-like multiplet structure was not observed in all the Co L2,3-edge XAS and XMCD, indicating that, even in the ultrathin samples, the Co atoms were not oxidized, and were more strongly spin polarized than those in the thicker samples. With decreasing CMG film thickness from 4 ML to 2 ML, the spin magnetic moment of Mn increased and the Mn L2,3-edge XAS did not show a Mn2+-like multiplet structure films in contrast to the Co-rich CMG thin films as studied by Asakura et al. [PRB, 82, 184,419 (2010)], where the Mn atoms are strongly oxidized. The results show that Mn-rich CMG films are beneficial for device fabrications in spintronics when the film thickness has to be reduced to a few monolayers.