Effects of off-stoichiometry on the spin polarization at the Co2MnβGe0.38/MgO interfaces: X-ray magnetic circular dichroism study

We have studied the electronic and magnetic states of Mn and Co atoms at the Co2Mn beta Ge0.38 (CMG)/MgO (beta = 0.67-1.8) interfaces, which constitute CMG/MgO/CMG magnetic tunnel junctions, by means of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroisms (XMCDs) at the Mn and Co L-2,L-3 edges and compared the deduced Co andMnmagnetic moments by the density-functional calculations with the coherent potential approximation (CPA). As the Mn content beta increased, the intensity of Mn L-2,L-3 XMCD decreased, in agreement with the result of the CPA calculation, which showed the resultant reduction of charges and spin moment on Mn atoms because of the delocalization of Mn 3d electrons with increasing beta. The Co spin magnetic moment for all the samples increased with decreasing beta, again consistent with the present calculation and the previous density-functional calculation by Picozzi et al. that the Co-Mn antisite has a larger magnetic moment than that of Co atoms at the regular sites and reduces the spin polarization at the Fermi level and hence the tunnel magnetoresistance ratio.