Modulated magnetic structure of Fe3PO7 as seen by Fe-57 Mossbauer spectroscopy

Article

关键词: HYPERFINE INTERACTION;    SHIFT;    IRON;   

DOI  :  10.1103/PhysRevB.97.104415

来源: SCIE

【 摘 要 】

The paper reports results of the Fe-57 Mossbauer measurements on an Fe3PO4O3 powder sample recorded at various temperatures, including the point of magnetic phase transition T-N approximate to 163K. The spectra measured above T-N consist of a quadrupole doublet with high quadrupole splitting of Delta(300K) approximate to 1.10mm/s, emphasizing that Fe3+ ions are located in crystal positions with a strong electric-field gradient (EFG). To predict the sign and orientation of the main components of the EFG tensor, we calculated the EFG using the density-functional-theory approach. In the temperature range T < T-N, the experimental spectra were fitted assuming that the electric hyperfine interactions are modulated when the Fe3+ spin (S) rotates with respect to the EFG axis, and with the emergence of spatial anisotropy of the hyperfine field H-hf alpha <(A)over tilde> center dot S at Fe-57 nuclei. These data were analyzed to estimate the components of the anisotropic hyperfine coupling tensor ((A) over tilde). The large anharmonicity parameter, m approximate to 0.94, of the spiral spin structure results from easy-axis anisotropy in the plane of the iron spin rotation. The temperature evolution of the hyperfine field H-hf (T) was described by the Bean-Rodbell model, which takes into account that the exchange magnetic interactions are a strong function of the lattice spacing. The obtained Mossbauer data are in qualitative agreement with previous neutron-diffraction data for a modulated helical magnetic structure in strongly frustrated Fe3PO4O3.

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