Inelastic Neutron scattering studies of CaMn7O12 based multiferroic compounds

CaMn7O12 is an interesting multiferroic material showing colossal electric polarization below the magnetic transition despite its helical magnetic structure with screw axis. Recently, we have studied the sample by doping trivalent La at the Ca site and a large change in polarization is observed. The multiferroicity in CaMn7O12 is still a matter of debate and at least two possible mechanisms are mooted in the literature. We propose here to perform inelastic neutron scattering experiment on the polycrystalline samples to investigate the spin wave excitations in the parent CaMn7O12 compound and its La derivatives to resolve the issue. The experiment will probe several other novel properties such as spin-gap, crystal field anomalies and will help us to provide a microscopic picture of magnetic interactions pathways and their natture relative strength.

CaMn7O12是一种极具研究价值的多铁性材料（multiferroic material）：尽管其磁结构为带有螺旋轴的螺旋磁构型，却可在磁相变温度以下展现出巨电极化效应。近期，我们通过在钙位掺杂三价镧（La）对该样品开展了相关研究，观测到电极化发生了显著改变。目前CaMn7O12的多铁性机制仍存在广泛争议，已有文献中至少提出了两种可供探讨的作用机理。为此，我们提议针对该体系的多晶样品开展非弹性中子散射（inelastic neutron scattering）实验，以研究母体CaMn7O12及其镧掺杂衍生物中的自旋波激发过程，从而厘清这一争议问题。该实验还将探测自旋隙、晶体场反常等多项新奇物性，有助于我们阐明磁相互作用的路径及其相对强度的本质，构建起磁相互作用的微观物理图景。