Magneto-optical investigation of the electronic and magnetic structure ofUAsxSe1−x

The magneto-optical Kerr rotation and ellipticity of different $\mathrm{U}{\mathrm{As}}_x{\mathrm{Se}}_{1-x}$ single crystals has been measured in magnetic fields up to 10 T at variable temperatures for photon energies between 0.5 and 5.7 eV. In addition the optical reflectivity between 0.03 and 12 eV has been determined. The complex diagonal and off-diagonal conductivity tensor elements have been calculated and an interpretation in terms of the electronic structure is presented. We obtain evidence for delocalized narrow $f$ states with equal bandwidth and similar oscillator strength of the $f\to d$ transition in the chalcogenide and the pnictide. A negative conduction-electron spin polarization is found for ferromagnetic USe as well as for UAs in the ferrimagnetic phase. For As-rich compositions, which exhibit a low conduction-electron concentration, we find for the first time in an actinide compound a magnetic red-shift of the $f\to d$ transition energy of the order of 150 meV. The total $f$ moment is shown to consist of antiparallel spin and orbital contributions with a dominating orbital part. Furthermore, we present the determination of the magnetic phase diagram of UAs using the magneto-optical Kerr effect.