Gigantic magnetoelectric effect in ferroelectric-magnets

在本研究中，我们开发了具有巨大磁电效应的磁性铁电氧化物。我们可以通过磁场来控制材料中的电极化，即巨大的磁电效应，有时也可以通过电场来控制磁性结构本身，即相互作用。还观察到巨大的光磁电（磁手性）效应。我们以实现巨大磁电效应为目标，基于时空对称性破缺、电子相的多临界性、晶格中的手性和自旋的受挫性，发现了新的磁性铁电体。在钙钛矿型锰矿RMnO_3、Pr(Sr, Ca)_2Mn_2O_7、尖晶石CoCr_2O_4和低维挫折氧化物Cu(Fe, Al)O_2、LiCu_2O_2中发现了磁性铁电，其极化受磁场控制。此外，通过同步加速器x射线辐射和中子散射研究证实了磁手性随外加电场的变化。巨大的光磁电效应为光通信中的光隔离器等新型光学器件提供了广阔的应用前景。我们成功地合成了稀土金属掺杂（Ba, Sr）TiO_3， La_2Ti_2O_7等的单晶，并观察了由于光磁电效应而产生的发射光谱。此外，我们还在LaMnO_3/SrMnO_3/LaAlO_3三色超晶格的磁性界面上观察到了光磁电响应。在与理论小组的合作中，我们证明了这些效应的起源是非常规的磁电耦合，其特征是自旋电流和环向矩的数量。我们认为这对新自旋电子学的发展做出了巨大的贡献。

In this study we have developed the magnetic ferroelectric oxides which may host the gigantic magnetoelectric effect. We could control the electric polarization in the materials by magnetic field as the gigantic magnetoelectric effect, and some times the magnetic structure itself by electric field as the reciprocal effect. The gigantic optical magnetoelectric (magneto-chiral) effect was also observed.We have aimed at the realization of the gigantic magnetoelectric effect, and found new magnetic ferroelectrics based on the time and space symmetry breaking, multicriticality of electronic phases, and the chirality in lattices and frustration of spins. We have found magnetic ferroelectricity in perovskite type manganites RMnO_3 and Pr(Sr, Ca)_2Mn_2O_7, spinets CoCr_2O_4, and low dimensional frustration oxides Cu(Fe, Al)O_2, and LiCu_2O_2, in which polarization was controlled by magnetic field. Furthermore the change of the magnetic chirality with external electric field was confirmed by synchrotron x ray radiation, and neutron scattering studies.The gigantic optical magnetoelectric effect has various potentials for the new optical devices such as an optical isolator in the optical communication. We have succeeded in the synthesis of the single crystals of the rare earth metal doped (Ba, Sr)TiO_3, La_2Ti_2O_7 and so on, and observed the emission spectra due to the optical magnetoelectric effect. Moreover, we observed the optical magnetoelectric response stem from the magnetic interface of the tailor-made tricolor superlattice of LaMnO_3/SrMnO_3/LaAlO_3.In collaboration with theory groups, we show the origins of these effects are the unconventional magnetoelectric coupling characterized by the quantities of spin current and toroidal moment. We believe that this made a great contribution to the progress of the new spintronics.