Multiferroicity and structural anomalies in Quadruple Perovskite Manganites: case study (A)Mn7O12, A = Na and La

Abstract

In this work we study the quadruple perovskite structure manganese oxides NaMn7O12 and LaMn7O12 under the point of view of multiferroicity, magnetoelectric coupling, and also structure anomalies on NaMn7O12. These studies range from the existence to the mechanism of the establishment of multiferroicity and coupling between ferroic orders in these materials. The driving force of the dynamic structural anomalies in NaMn7O12 are also studied with the goal of clarifying the mechanisms of structural distortion and how they relate to the onset of ferroic orders. The results of IXS and DXS experiments show interesting dynamical anomalies in NaMn7O12's structural transition, a softened phonon at the structural modulation wavevector that was shown to be related to diffuse x-ray peaks with a different wavevector point in the direction of competing distortions and that the Jahn-Teller mechanism driven distortion overcome its competitor. A ferroelectric transition was found simultaneous to anomalies in specific heat and magnetization in NaMn7O12. Magnetic hysteresis loops are quite wider in the ferroelectric phase. These properties are explained in function of a magnetoelectricity mediated antiferromagnetic domain wall ordering model. As for LaMn7O12, a ferroelectric transition at the B site antiferromagnetic transition temperature. Besides the particularities of each system, structural and magnetic properties imply that their ferroelectricity is of magnetic origin through the exchange striction mechanism.