The investigation of mechanisms of the magneto-optical activity of rare-earth iron garnet single crystals

The magnetic and magneto-optical properties (MO) of the typical representatives of three rare-earth iron garnets (RIG) groups: (1) with heavy rare-earth elements Yb, Er, Dy, Tb; (2) with elements from the middle of lanthanide series Gd, Sm; (3) with light rare-earth element Nd are presented. In contradistinction to other work on the Faraday rotation (FR), which were done only at 1152 nm (8696 cm−1); here, we present FR spectra obtained in the energy region 5500–20,000 cm−1 with high optical resolution. The investigations have been done at temperatures of 5, 82, 130 and 295 K using magnetic field up to 25 kOe applied parallel to the [1 1 1] crystallographic axis of the crystals.It has been shown that the contribution proportional to the magnetic field and independent of temperature to the mixing of the ground state multiplets exceeds the paramagnetic contribution in YbIG, ErIG, GdIG and SmIG. In Tb and Dy iron garnets contributions from the two mechanisms have opposite signs, and the paramagnetic mechanism gives the greatest contribution to FR. Nevertheless, the contribution of the diamagnetic mechanism, caused by the influence of the exchange field in the iron-sublattices on R ions, is significant, and it is necessary to take it into account. Anomalously large MO activity is observed in NdYIG. This is the result of contributions of in the same sign and approximately equal magnitude from the paramagnetic and diamagnetic mechanisms.