MAGNETISM OF HGSE-FE

The perpendicular and parallel components of the magnetization of the mixed valence system Hg1-xFexSe in the strongly dilute limit x<10(-3)) have been measured in magnetic fields up to 20T. In this interesting semimagnetic semiconductor the overall magnetization is caused simulta neously by Fe3+ (Brillouin paramagnet), Fe2+ (van Vleck paramagnet), a nd free electrons (diamagnetic de Haas-van Alphen effect). Using a tor que magnetometer the various contributions with their anisotropy are i ndividually determined. For very low iron content (x<2.4x10(-4)) the F e donors exclusively exhibit an isotropic Brillouin paramagnetism of n oninteracting Fe3+ ions. For higher concentration Fe2+ also exists. Co existing with a crystal-field-induced anisotropy. This anisotropy is a nalyzed by measuring the induced magnetic moment perpendicular to the magnetic field when applying the field in a nonsymmetric direction of the crystal. Using recent theoretical results on the energy-level diag ram of Fe2+ in the T-d symmetry of a HgSe host lattice we deduce a spi n-orbit level splitting of 2 meV from our experimental data. In contra st to higher concentration samples, both the Brillouin paramagnetism o f Fe3+ and the van Vlec paramagnetism of Fe2+ can be attributed to the sum from individual Fe donors with no obvious magnetic interaction be tween them. Finally, we also have measured de Haas-van Alphen oscillat ions of the conduction-band electrons with amplitudes of the same orde r as the paramagnetic background. From the measured crystal-field-indu ced anisotropy in the magnetic moment we deduce a Fermi-surface anisot ropy of about 7%.