Site preference of the 3 d transition metal ions in the Mn 4 − x Fe x Nb 2 O 9 compounds as revealed by Mössbauer spectroscopy

In this paper, we report on structural, magnetic, Mössbauer spectroscopy and density functional theory (DFT) studies of the Mn 4 − x Fe x Nb 2 O 9 compounds. Temperature dependent magnetization measurements have shown that the paramagnetic to antiferromagnetic transition temperatures, T N , depend non-linearly on the Fe doping level x , which is different from earlier studies on similar compounds of Mn 4 − x Co x Nb 2 O 9 . More interestingly, our Mössbauer spectroscopy measurements have revealed preferential occupation of the 3 d transition metal ions, namely, the Fe(Mn) atoms prefer to occupy the highly buckled M-II(relative flat M-I) site, which can be well understood by the band mixing behavior from our DFT calculations. These results are expected to be important for a better understanding of the rich physics of this family of compounds, especially when one concerns the interpretation of experimental results of similar mixing compounds.