Mössbauer spectroscopy of the magnetic-field-induced ferroelectric phase of CuFeO₂

⁵⁷ Fe Mössbauer spectroscopy in an applied magnetic field has been conducted on single crystals of CuFeO₂ and CuFe _0.965Ga_0.035O₂ in order to investigate magnetic-field-induced ferroelectric states. The Mössbauer spectra observed under a magnetic field change significantly, corresponding to magnetic- field-induced phase transitions. In the ferroelectric incommensurate (FEIC) phase (7 < H_ex < 13 T), the spectrum can be explained by a model with spins distributed at approximately 20, 95, and 160° from the c-axis in the (110) plane. This spin configuration resembles the "complex noncollinear spin configuration (CNC) " model proposed theoretically. In the FEIC phase, the isomer shift is larger, while the quadrupole splitting and average hyperfine field are smaller than those in the collinear four sublattice (4SL, 0 < H_ex < 7 T) and five sublattice (5SL, H _ex > 13 T) phases. In addition, a noticeable change in the hyperfine field is observed with varying magnetic fi eld. We consider that these changes indicate the change in the electronic state of the Fe³⁺ ion, possibly modified by a spin-orbit interaction.