Effect of crystal symmetries and phase boundaries on the magnetoelectricity of La2NiMnO6 prepared under ambient conditions.

La₂NiMnO₆ prepared under ambient conditions are analyzed for their crystal phase symmetry via powder x-ray diffraction in the laboratory as well as synchrotron sources and neutron powder diffraction. The room temperature symmetry is found to be R − 3 c for samples having a sintering temperature less than 800 °C and gradually increasing participation of P 2 1 / n symmetry is observed for higher sintering temperature samples. A crystallographic phase transition at ∼650 K from biphasic (R − 3 c + P 2 1 / n) to monophasic (R − 3) for all samples is observed. This transition is found to be endowed with a small amount of magnetic ordering at the transition temperature. The measured magnetoelectricity on these samples displayed their direct dependence on relative crystal phase symmetries, such that magnetoelectricity is highest for the equifraction content of R − 3 c and P 2 1 / n symmetries. The temperature variation of the first order magnetoelectric coefficient is observed to be proportional to T − 0.25 _, which is analogous to the Mott variable range hopping conduction exhibited by these compounds. Corroboration of observed results suggests the interfacial origin of magnetoelectricity in these samples. [ABSTRACT FROM AUTHOR]