Effects of off-stoichiometry on the spin polarization at the Co_2Mn_βGe_(0.38)/MgO interfaces: X-ray magnetic circular dichroism study

摘要

We have studied the electronic and magnetic states of Mn and Co atoms at the Co_2Mn_βGe_(0.38) (CMG)/MgO (β = 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 L23 edges and compared the deduced Co and Mn magnetic moments by the density-functional calculations with the coherent potential approximation (CPA). As the Mn content β increased, the intensity of Mn L_(2,3) 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 β. The Co spin magnetic moment for all the samples increased with decreasing β, 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.