Understanding Complex Interplay among Different Instabilities in Multiferroic BiMnO Using Fe Probe Mössbauer Spectroscopy.

Here, we report the results of a Mössbauer study on hyperfine electrical and magnetic interactions in quadruple perovskite BiMnO doped with Fe probes. Measurements were performed in the temperature range of 10 K < < 670 K, wherein BiMnFeO undergoes a cascade of structural ( ≈ 590 K, ≈ 442 K, and ≈ 240 K) and magnetic ( ≈ 57 K, ≈ 50 K, and ≈ 24 K) phase transitions. The analysis of the electric field gradient (EFG) parameters, including the dipole contribution from Bi ions, confirmed the presence of the local dipole moments , which are randomly oriented in the paraelectric cubic phase ( > ). The unusual behavior of the parameters of hyperfine interactions between and was attributed to the dynamic Jahn-Teller effect that leads to the softening of the orbital mode of Mn ions. The parameters of the hyperfine interactions of Fe in the phases with non-zero spontaneous electrical polarization (), including the 1 ↔ transition at , were analyzed. On the basis of the structural data and the quadrupole splitting Δ() derived from the Fe Mössbauer spectra, the algorithm, based on the Born effective charge model, is proposed to describe () dependence. The () dependence around the ↔ 2/ phase transition at is analyzed using the effective field approach. Possible reasons for the complex relaxation behavior of the spectra in the magnetically ordered states ( < ) are also discussed.