Magneto-optical Kerr-effect of uranium compounds: A study of the electronic structure

Abstract

A comprehensive study of the magneto-optical properties of metallic uranium compounds is presented in the 0.5–6 eV photon energy range. New results about the electronic and the magnetic structure of these materials are derived. The f states are best described in an itinerant model with an occupation of nearly 3 for all investigated materials except the Th 3P 4-structure compounds, although correlation effects are shown to play a dominant role in UTe. A spin-polarized band structure of f and d states in the system UTe-USb-YSb is derived and the competition of f-d and f-p hybridization in this system is discussed. The maintenance of a f 3−f 2 valence transition in the USb-YSb pseudo-binary system is challenged. The magnetic f-d exchange energy is established to be negative for all investigated materials i.e the f and d moments allign antiparallel upon magnetic ordering. This property manifests itself in two magneto-optical effects: Firstly, the conduction electron spin-polarization displays a negative sign and its size is observed to range up to – 100% for certain compounds, which is an extraordinary value for magnetic metals. Secondly, the f → d transition energy displays a magnetic red-shift in the order of 200 meV due to the formation of spin-polarized subbands of the d states which are energetically split by the exchange energy. The size of the magnetic shift is found to depend on the sublattice magnetization rather than on the net moment which results in similar magnitudes for some ferro- and antiferromagnets. This behavior completely differs from the one known up to now for antiferromagnetic semiconductors, but is well understood in terms of the magnetic structure of the uranium pnictides. For most of the materials, the value of the f polarization is calculated. The f moment itself is evidenced to consist of antiparallel spin and orbital contributions with a predominant orbital part in most of the investgated NaCl-structure compounds. Some of the investigated uranium systems seem to be very promising candidates for technical applications due to the by far largest Kerr-rotation ever observed for metals, reaching up to ≈ 9.2° at 65% reflectivity.