SEMINAR      Friday, 23 January 2004 - h. 11:00  Auditorium B. Touschek     A. Kuzmin Institute of Solid State Physics, University of Latvia and Excellence Centre of Advanced Material Research and Technology (CAMART)   Structural, optical, vibrational and magnetic properties of NiO-MgO system Abstract NiO-MgO system belongs to diluted antiferromagnets, whose magnetic properties are determined by chemical composition. The seminar will be devoted to the overview of complex investigations of polycrystalline and single-crystal NiO-MgO solid solutions using x-ray absorption spectroscopy, x-ray diffraction, optical absorption, luminescence and Raman spectroscopies. We found that opposite to conventional point of view, the local symmetry at Ni2+ ions sites lowers upon dilution due to magnetic interactions between neigbouring nickel ions. Both one-magnon and two-magnon excitations contribute strongly to optical and Raman spectra. Two-magnon energy dependence on composition and temperature and one-magnon energy dependence on temperature follow expected behaviour. One-magnon energy dependence on composition shows unexpected trend.