Effect of coupled ferroelectric and antiferromagnetic fluctuations on dielectric anomalies in spin induced multiferroics.

Dielectric and magnetodielectric peaks have been evidenced by ε(T, H) measurements in spin induced ferroelectrics: CuCrO(2) and AgCrO(2) delafossites. Such behaviour, also found in several other improper ferroelectrics, can be explained in the frame of Landau analysis of phase transitions with two coupled order parameters: antiferromagnetic ordered moment, L, and polarization, P. The existence of such anomalies in the dielectric constant observed at T(N) is very general. The existence of this peak is not due to any linear coupling term between P and L in this system, but rather due to the L(2)P(2) term which always exists in every compound, whatever the symmetry/space group is.