ANISOTROPY OF THE FARADAY ROTATION IN PRASEODYMIUM GALLIUM GARNET SINGLE CRYSTALS

Abstract

Faraday Rotation (FR) measurements performed on single crystals Praseodymium Gallium Garnet (PrGaG) at 0.6328 and 1.15 micron wavelengths are reported in a continuous magnetic field up to 20 kOe which was parallel to the three main crystallographic directions, over the temperature range 6-300 K. On the same samples, the magnetic properties are investigated. At 0.6328 micron wavelength, the Verdet constant V is found anisotropic : below 130 K, [100] corresponds to the weakest rotation. No anisotropic behaviour is observed at 1.15 micron wavelength. The reciprocal Verdet constants (V) and the inverse of the magnetic susceptibility (x) are found rigourously proportional to the temperature. The ratio V/ appears temperature independent in agreement with the model of Van Vleck and Hebb above about 80 K. These results are briefly discussed in terms of strongly and weaky allowed electric dipole transitions. In paramagnetic materials, it has been admitted since the historical work of Van Vleck and Hebb (1) that the Verdet constant and the magnetic susceptibility should exhibit identical temperature dependences. Although a lot of work has been devoted to this subject, some essential features remain unclear to this day due to the absence of precise experimental data in a large domain of temperature. Furthermore very few results concerning the anisotropic character of the Faraday Rotation have been reported and, to our knowledge, the properties of the erbium iron garnet (2) and of the ytterbium gallium garnet (3) have been investigated only. In this last crystal, it has heen observed the singular fact that when the magnetic properties are rigorously isotropic the Verdet constaut is anisotropic