Recent progress in magneto-optics and research on its application (Review Article)

Анотація

We have investigated various kinds of magneto-optical properties for rare earth orthochromites. In RCrO₃(R = Tb, Dy and Ho), from the analysis of Cr³⁺ exciton absorption, it was elucidated that these compounds exhibit an anomalous spin-reorientation under the magnetic field along the b axis, where the weak ferromagnetic moment of the Cr³⁺ spins rotates in the ac plane perpendicular to the b axis. In these compounds, when the R³⁺ spin configuration is disordered, an anomalous satellite band appears in the lower energy side of the Cr³⁺ exciton absorption, which is associated with the breakdown of k = 0 selection rule caused by the disorder of R³⁺ spin configuration. In YbCrO₃, various kinds of cooperative excitations such as Cr³⁺ exciton coupled with Yb³⁺ magnon and Cr³⁺-Yb³⁺ exciton molecule appear in the visible region, which are induced by the antisymmetric exchange interaction between the Cr³⁺ and Yb³⁺ spins. The propagation of these cooperative excitations strongly depends on the spin structure and the external magnetic field. In ErCrO₃, a photo-induced spin-reorientation takes place within 50 ms after the photo-irradiation corresponding to the ⁴A_2g ®²E_g transition of Cr³⁺, and it returns to the initial spin configuration in about 400 ms. This phenomenon was detected by the time-resolved Er³⁺ absorption spectra corresponding to the ⁴I_15/2®⁴I_9/2 transition. Finally, we briefly review the recent frontier research on application mainly developed in Japan.