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. 207Pb 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 β ≈ 0.15 × 10−15 s A−1 (x = 0.4) and 0.54 × 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 dM2/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.