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

Various kinds of magneto-optical properties are investigated in rare earth orthochromites. From an analysis of Cr3+ exciton absorption in RCrO3 (R=Tb, Dy, and Ho), it is unferred that these compounds exhibit an anomalous spin-reorientation in a 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 on the lower-energy side of the Cr3+ exciton absorption, which is associated with the breakdown of the k=0 selection rule due to the disorder of the R3+ spin configuration. In YbCrO3, various kinds of cooperative excitations, such as a Cr3+ exciton coupled with an Yb3+ magnon and a Cr3+−Yb3+ exciton molecule, which are induced by the antisymmetric exchange interaction between the Cr3+ and Yb3+ spins, appear in the visible region. The propagation of these cooperative excitations depends strongly on the spin structure and the external magnetic field. In ErCrO3, a photo-induced spin-reorientation takes place within 50 μs after the photo-irradiation corresponding to the A2g4→2Eg transition of Cr3+, and it returns to the initial spin configuration in about 400 ms. This phenomenon is detected in the time-resolved Er3+ absorption spectra corresponding to the I15/24→4I9/2 transition. Finally, we briefly review the recent frontier research on applications developed mainly in Japan.