Spin-flop driven magneto-dielectric effect in Co4Nb2O9

Co4Nb2O9 becomes antiferromagnetic (AFM) below 27.4 K with a spin-flop transition at a critical field, H-c, of 12 kOe. Room-temperature dielectric properties are dominated by finite electronic conductivity. Below 125 K, the charge carriers are frozen-out and the dielectric constant is controlled by the lattice phonons. A large (12%) spin flop-driven enhancement in dielectric constant is found in the very narrow temperature interval (Delta T = 1.6 K) in the vicinity of the AFM phase transition. Magneto-dielectric anomaly shows low-frequency dispersion; therefore, the H-induced changes in the phonon eigenfrequencies are unlikely. Other possible reasons for unusual magneto-dielectric effect in Co4Nb2O9 are discussed. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3645017]