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The search for multiferroic order in a single phase of bismuth pyrochlore has been unsuccessful so far. In this direction, our study unveiled the capability of a biphase of bismuth pyrochlore and spinel in hosting a multiferroic order at room temperature. A complex oxide biphase of cubic pyrochlore and cubic spinel crystals acquired in the Bi2O3-Nb2O5-2MnCO3-Fe2O3 system revealed the crystals of a spinel phase (Fe1.59(3)Mn1.39(3)O4.26(7)) intergrown in the dense pyrochlore (Bi1.35(1)Fe0.64(1)Nb1.26(1)Mn0.75(1)O6.39(5)) matrix. The average composition of the components of the investigated biphase was determined using an electron probe microanalyzer (EPMA). The structural features indicated the presence of large ionic displacements within the cubic pyrochlore phase as seen from the appearance of 442 reflection in the X-ray diffraction pattern and infrared active mode at ∼64 cm−1 in the Raman spectrum recorded at room temperature. The pyrochlore single-phase composition (Bi1.35(1)Fe0.64(1)Nb1.26(1)Mn0.75(1)O6.39(5)), as suggested from a thorough EPMA microstructural analysis, exhibited broad dielectric relaxation and an overall paramagnetic behavior. The observation of disordered superparamagnetism as well as dielectric relaxation in the biphase conformed to that of a relaxorlike multiferroic behavior at room temperature. Moreover, self-biased magnetoelectric voltage coefficients of 0.60 mV/cm Oe at 100 Hz and 5.54 mV/cm Oe at 1 kHz were detected between magnetization and electric polarization at room temperature. Therefore, the composite of such a pyrochlore and spinel with an inherent property of strong spin–orbit and spin–lattice coupling will be interesting from theoretical and experimental point of view in the arena of magnetoelectrics.

Herein, we report a Na deficient single phase sodium bismuth titanate perovskite exhibiting ferromagnetism with reduced leakage conductivity and a self-biased high magnetoelectric (ME) coupling coefficient at room temperature (27 °C). Observed ferromagnetism is induced by sodium cation vacancy dominated by spin polarization of holes in the valence band. An unexpected high ME coupling coefficient of about 4.18 mV/cm Oe, observed at zero DC magnetic bias field, is relatively large and juxtapose to other single phase multiferroics including BiFeO3. This study opens up an altered strategy in designing multiferroic materials with reinforced ME coupling at room temperature.

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