Magnetic field tunable dielectric dispersion in successive field-induced magnetic phases of the geometrically frustrated magnet CuFeO2 up to 28 T

We find magnetic-field-dependent dielectric dispersions specific to successive field-induced magnetic phases of a geometrically frustrated magnet ${\mathrm{CuFeO}}₂$ up to 28 T. The dielectric dispersions in the three field-induced collinear-commensurate magnetic phases are well described by the superposition of Debye-type relaxations, and the number of contributions to the Debye-type dispersions differs in these phases. In contrast, the dielectric dispersions in the noncollinear-incommensurate phase, known as a spin-driven ferroelectric phase, cannot be simply described by the Debye-type relaxations. In addition, we find that the temperature dependence of the Debye relaxation frequencies follows the Arrhenius law, and that the activation energies derived from the Arrhenius equation also depend on the magnetic field. Considering the magnetostriction effect in combination with elongation/contraction of spins resulting from the application of a magnetic field, we show that the number of Debye relaxation components is equivalent to the number of states of local ${\mathrm{Fe}}₃\mathrm{O}$ clusters determined by oxygen displacement within a triangular Fe lattice. Based on this correspondence, we propose a possible explanation that excess charges resulting from a lack of stoichiometry hop over the double-well potentials within each local ${\mathrm{Fe}}₃\mathrm{O}$ cluster, like small polarons.