Room-temperature paramagnetoelectric effect in magnetoelectric multiferroics Pb(Fe1/2Nb1/2)O3 and its solid solution with PbTiO3

We have observed the magnetoelectric (ME) response at room temperature and above in high-resistive ceramics made of multiferroic Pb(Fe1/2Nb1/2)O-3 (PFN) and PFN-based solid solution 0.91PFN-0.09PbTiO(3) (PFN-PT). The value of the paramagnetoelectric (PME) coefficient shows a pronounced maximum near the ferroelectric-to-paraelectric phase transition temperature, T (C,) and then decreases sharply to zero for T > T (C). The maximal PME coefficient in PFN is about 4 x 10(-18) s/A. The theoretical description of the PME effect, within the framework of a Landau theory of phase transitions allowing for realistic temperature dependences of spontaneous polarization, dielectric and magnetic susceptibilities, qualitatively reproduces well the temperature dependence of the PME coefficient. In particular, the Landau theory predicts the significant increase of the PME effect at low temperatures and near the temperature of the paraelectric-to-ferroelectric phase transition, since the PME coefficient is equal to the product of the spontaneous polarization, dielectric permittivity, square of magnetic susceptibility, and the coefficient quantifying the strength of the biquadratic ME coupling. An atomistic technique is further developed and used to further demonstrate that the PME effect can also be sensitive to the frequency of the applied magnetic field (when this frequency is of the order of GHz).