Spin and Orbital Ordering in the Quadruple Perovskite Solid Solution AMn₇O₁₂

Wei-Tin Chen^1,2*, Chin-Wei Wang³, Fang-Cheng Chou^1,2,3, Mark S. Senn⁴

¹Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
²Taiwan Consortium of Emergent Crystalline Materials, MOST, Taipei, Taiwan
³National Synchrotron Radiation Research Center, NSRRC, Hsinchu, Taiwan
⁴Department of Chemistry, University of Warwick, Coventry, UK

* Presenter:Wei-Tin Chen, email:weitinchen@ntu.edu.tw

Recently, CaMn₇O₁₂ is reported to be the Type-II multiferroic and exhibiting the largest magnetoelectric response to date. In order to have further understanding of the coupling between the crystal structure and physical properties, a series of A-site ordered quadruple perovskite AMn₇O₁₂ materials were prepared utilizing high-pressure high-temperature extreme conditions. Structural analysis with high resolution synchrotron x-ray and neutron diffraction techniques were performed and rich spin, charge and orbital couplings were observed in these metastable materials. We show that the hole and electron doping is associated only with an average valance change on the perovskite B-site evident through BVS calculated in the high temperature cubic Im-3 phase at 700 K. On cooling distinct crystallographic structures were shown in the solid solution materials. For A = La and Ca parent compounds, the previously reported monoclinic and rombohedral phases corresponding to C-type orbital ordering are observed. The Na rich end, on the other hand, exhibits a different type of monoclinic phases at low temperatures. Compositional phase diagram of the solid solution series were derived and recent discoveries of such exotic systems will be discussed in this presentation.

Keywords: high pressure synthesis, quadruple perovskite, orbital ordering, magnetism, x-ray and neutron diffraction