Laboratory for Multiscale Materials Experiments, Paul Scherrer Institut, CH 5232, Villigen-PSI, Switzerland.
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH 5232, Villigen-PSI, Switzerland.
Sci Rep. 2017 Mar 20;7:44753. doi: 10.1038/srep44753.
A current challenge in the field of magnetoelectric multiferroics is to identify systems that allow a controlled tuning of states displaying distinct magnetoelectric responses. Here we show that the multiferroic ground state of the archetypal multiferroic TbMnO is dramatically modified by epitaxial strain. Neutron diffraction reveals that in highly strained films the magnetic order changes from the bulk-like incommensurate bc-cycloidal structure to commensurate magnetic order. Concomitant with the modification of the magnetic ground state, optical second-harmonic generation (SHG) and electric measurements show an enormous increase of the ferroelectric polarization, and a change in its direction from along the c- to the a-axis. Our results suggest that the drastic change of multiferroic properties results from a switch of the spin-current magnetoelectric coupling in bulk TbMnO to symmetric magnetostriction in epitaxially-strained TbMnO. These findings experimentally demonstrate that epitaxial strain can be used to control single-phase spin-driven multiferroic states.
当前，磁电多铁性领域面临的一个挑战是确定能够对显示不同磁电响应的状态进行控制调节的体系。在这里，我们表明，原型多铁性材料 TbMnO 的多铁基态可通过外延应变显著改变。中子衍射表明，在高应变薄膜中，磁有序从类似体的非共辄 bc-回旋结构转变为共辄磁有序。与磁基态的改变相伴，光学二次谐波产生（SHG）和电测量表明铁电极化极大增强，并从沿 c 轴方向变为沿 a 轴方向。我们的结果表明，多铁性性质的剧烈变化源于体相 TbMnO 中自旋电流磁电耦合到外延应变 TbMnO 中对称磁伸缩的转变。这些发现从实验上证明了外延应变可用于控制单相自旋驱动的多铁态。
