Department of Materials Science, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK.
Sci Rep. 2017 Mar 3;7:43799. doi: 10.1038/srep43799.
BiMnO is a promising multiferroic material but it's ferromagnetic T is well below room temperature and the magnetic phase diagram is unknown. In this work, the relationship between magnetic transition temperature (T) and the substrate induced (pseudo-) tetragonal distortion (ratio of out-of-plane to in-plane lattice parameters, c/a) in BiMnO thin films, lightly doped to optimize lattice dimensions, was determined. For c/a > 0.99, hidden antiferromagnetism was revealed and the magnetisation versus temperature curves showed a tail behaviour, whereas for c/a < 0.99 clear ferromagnetism was observed. A peak T of up to 176 K, more than 70 K higher than for bulk BiMnO, was achieved through precise strain tuning. The T was maximised for strong tensile in-plane strain which produced weak octahedral rotations in the out-of-plane direction, an orthorhombic-like structure, and strong ferromagnetic coupling.
BiMnO 是一种很有前途的多铁材料，但它的铁磁居里温度远低于室温，其磁相图也不清楚。在这项工作中，我们确定了 BiMnO 薄膜中磁转变温度 (T) 与衬底诱导的（拟）四方畸变（面外与面内晶格参数之比，c/a）之间的关系，这些薄膜经过轻微掺杂以优化晶格尺寸。对于 c/a > 0.99，发现了隐藏的反铁磁性，磁化随温度的曲线呈现出尾部行为，而对于 c/a < 0.99，则观察到明显的铁磁性。通过精确的应变调谐，实现了高达 176 K 的 T 值峰值，比块状 BiMnO 高出 70 K 以上。T 的最大值出现在强拉伸平面应变下，这种应变在面外方向产生弱的八面体旋转，形成类正交结构，并产生强的铁磁耦合。
