Temperature Dependence of Extended X-ray Absorption Fine Structure of Multiferroic CaMn₇O₁₂

The local structure around Mn atoms in multiferroic CaMn7O12 were studied by x-ray absorption fine structure with temperature across magnetic/ferroelectric polarization transition temperature (TC = TP). There is no variation of electronic configuration near TC, but a change of the disorder distribution of Mn-O bond. The first shell peak was best fitted by multi-FEFF codes with three Mn occupations of CaMn(1)3+3[Mn(2)3+Mn(3)4+]4O12. The larger Dybe-Waller σ2 of Mn(1) manifests the larger distortion of Mn(1)-O distribution, which rises mainly from the variation of the bond length and/or coordination number (N). The fitted N of Mn(1) changes from 1.1 to 4.5 with the temperature decreasing. This indicates that the oxygen site shift towards the Mn(1) atom, making the average Mn(1)-O length short. Otherwise, the change of σ2 and Δr are tiny at Mn(2) and Mn(3) sites near TC. The local structural variation of Mn(1) site is thus may considered as related to the magnetic/ferroelectric polarization transition.