Room-temperature ferroelectricity, superparamagnetism and large magnetoelectricity of solid solution PbFe1/2Ta1/2O3 with (PbMg1/3Nb2/3O3)0.7(PbTiO3)0.3

We report the properties of first synthesized ceramic samples of a perovskite solid solution (PbFe1/2Ta1/2O3)(x)[(PbMg1/3Nb2/3O3)(0.7)(PbTiO3)(0.3)](1-x), x = 0.4, 0.5. The solution is a single-phase material contrary to broadly studied multiphase (magnetic/ferroelectric) composites. Both compounds are ferroelectrics with a diffuse phase transition. An increase in x value results in a decrease in phase transition diffuseness, and an increase in the remnant polarization. Pb-207 NMR shows that iron ions are nonuniformly distributed over octahedral sites and tend to random occupation of these sites in the perovskite structure. In particular, the NMR data indicate a tendency to form regions with a higher concentration of iron in the perovskite structure. Magnetic measurements show the coexistence of superparamagnetic and paramagnetic phases in the samples. The paramagnetoelectric (PME) coefficients determined by a dynamic method at room temperature have values beta approximate to 0.15 x 10(-15) s A(-1) (x = 0.4) and 0.54 x 10(-15) s A(-1) (x = 0.5) at low magnetic fields (+/- 300 Oe), which are three thousands times larger than that in most single-phase magnetoelectric materials. Our measurements show that the main contribution to the PME response is caused by the superparamagnetic phase. Because the ME response is proportional to dM(2)/dH, it can be amplified by many orders of magnitude for the multiferroics with the superparamagnetic phase due to a sharp change of magnetization with the field.