On the role of spin-orbit splitting in magneto-optics (abstract only)

Abstract

The interaction of photons with spins is mediated through spin-orbit coupling.Therefore, magneto-optics of magnetic materials depends crucially on the spin-orbitinteractions in either the initial and/or the final state of the optical transition considered and this makes magneto-optics a very powerful tool for the study of spin-orbit coupling in 3d, 4f and 5f materials. This paper will review some of themost striking results obtained over the last 30 years(For the data up to 1990 see: Schoenes J 1991 Materials Science and Technology Vol 3A Electronic and Magnetic Properties of Metals and Ceramics eds. R W Cahn, P Haasen and E J Kramer (Weinheim: VCH)p147).The largest ever reported Faraday rotations exceed 2×10 6 deg cm-1. They have beenobserved in thin films of the europium monochalcogenides EuS, EuSe and EuTe, which have a 4f 7( 8S7/2) groundstate, i.e. no spin-orbit splitting in the initial state.The occurrence of the large magneto-optical signal is therefore clear evidence for a largespin-orbit interaction in the final state of the responsible transition. A line shape analysis shows that this final state consists of a coupling of the excited 5d electronwith the remaining 4f 6 state. Nd3S4 is an example of a system with spin-orbitcoupling in the initial as well as in the final state. The diamagnetic line shape helps toidentify the coupling in the final state and the spin-orbit parameter can be determined.While the intrinsic value of the Kerr rotation of CeSb is still debated, agreement exists that inany case CeSb has the largest Kerr rotation. Of particular interest is the transition froma paramagnetic line shape to a diamagnetic line shape, when the magnetization is reduced from saturation.LaSe presents another archetypical example. Here the initial state is a non-magnetic 5d1state and the magneto-optical experiment allows one to study empty 4f states.In all these lanthanide compounds Russel-Saunders coupling could be applied to the initialand final states. This is no longer the case for the final state in actinide compounds.Magnetic circular dichroism and Faraday rotation measurements on UO2 films evidence that the final state for the excitation of an f electron out of the 5f 2 initial stateis near to a j-j coupled 5f 1-6d1 state. A different approach has to be made to interpretmagneto-optical data for uranium monochalcogenides. In the case of US, for example, 5fdelocalization and f-d hybridizations are too large to apply atomic models and sophisticated band structure calculations are needed to account for the spectra.Besides interband transitions, magneto-optics has also proven to be powerful for studying free carriers. Two different types of frequency dependencies have been predicted by theory.Examples of these two kinds will be presented in the form of data for TmSe and U3P4. Thespecial case of CrPt3 will be discussed in a separate paper.