Investigation of magneto-electric optical effect

我们研究了被称为“磁电光学效应”和“磁手性效应”的新的磁光效应。在这些光学效应中，去偏振光的光学响应取决于传播矢量的方向。我们研究了铁磁体、GaFeO_3和尖晶石型Fe_3O_4单晶的光学性质，以阐明磁电光学效应和磁手性效应的机理。GaFeO_3在低温下具有自发磁化和电极化，表明空间反转对称性和时间反转对称性的破坏，而Fe_3O_4具有局域空间反转对称性。在1.0-2.5 eV能区，研究了极性铁磁体GaFeO_3的磁电光学效应，即光传输方向反转时光吸收的变化。此外，我们还发现了一种新的磁光效应，称为X射线非互易方向二向色性，即铁离子在K边附近的X射线吸收取决于X射线传播矢量是平行还是反平行于GaFeO_3中磁化和电极化矢量的外部产生。这些光学响应显示出对电极化和磁化强度的明显依赖关系，表明这些光学效应与环向力矩之间的关系。X射线非互易方向二向色性谱可以用来证明磁干扰和纳米结构等非中心对称体系的局域磁性。我们不仅在GaFeO_3中发现了X射线非互易方向二向色性，而且在Fe_3O_4中也发现了非互易方向二向色性。

We have investigated the new magneto-optical effects termed "magneto-electric optical effect" and "magneto-chiral effect". In these optical effects, the optical response of the depolarized light depends on the direction of the propagator vector. We studied the optical features in the single crystals of the ferrimagnet, GaFeO3, and spinel-type Fe3O4 in order to clarify the mechanism of the magneto-electric optical effect and magneto-chiral one. GaFeO3 has spontaneous magnetization and electric polarization at low temperatures, indicating the breakdown of the space inversion symmetry and the time reversal one, while Fe3O4 has local space inversion symmetry.The magneto-electric optical effect, i.e., the change of optical absorption upon the reversal of the light propagation direction, has been investigated for the polar ferrimagnet GaFeO3 in the energy region of 1.0-2.5 eV. Moreover, we have found a novel magneto-optical effect, termed x-ray nonreciprocal directional dichroism, that the x-ray absorption at around the K edge of an Fe ion depends on whether the x-ray propagation vector is parallel or antiparallel to the outer production of the magnetization and electric-polarization vectors in GaFeO3. These optical responses show the obvious dependence on the electric polarization and magnetization, suggesting the relationship between these optical effects and the toroidal moment. The x-ray nonreciprocal directional dichroism spectroscopy as demonstrated here can be a useful tool to prove the local magnetism in noncentroysymmetric systems such as magnetic interferences and nanostractures. We have found the x-ray nonreciprocal directional dichroism not only in GaFeO3 but also Fe3O4.