Gigantic magnetoelectric effect in ferroelectric-magnets

在本研究中，我们发展出具有巨磁电效应的磁性铁电氧化物。我们可以通过磁场的巨磁电效应来控制材料中的电极化，有时也可以通过电场的互逆效应来控制材料中的磁性结构。我们以实现巨磁电效应为目标，基于时空对称性破缺、电子相的多临界性、晶格中的手征性和自旋的阻挫，发现了新的磁性铁电体。我们在钙钛矿型锰氧化物RMnO_3和Pr（Sr，Ca）_2Mn_2O_7、尖晶石型CoCr_2O_4以及低维阻挫氧化物Cu（Fe，Al）O_2和LiCu_2O_2中发现了磁性铁电性，它们的极化受磁场控制。此外，通过同步辐射X射线辐射和中子散射研究证实了磁手征随外电场的变化，这种巨大的光磁电效应在光通信中的光隔离器等新型光器件中具有广阔的应用前景。我们成功地合成了稀土掺杂的（Ba，Sr）TiO_3，La_2Ti_2O_7等单晶，并观察到了光磁电效应的发射光谱。此外，我们还观察到了由LaMnO_3/SrMnO_3/LaAlO_3三色超晶格的磁界面产生的光磁电效应。与理论组合作，我们发现这些效应的起源是以自旋电流和环向矩为特征的非常规磁电耦合。我们认为这对新自旋电子学的发展作出了巨大贡献。

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.