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RESEARCH PRODUCT

<title>Raman scattering by phonons and magnons in Ni<formula><inf><roman>c</roman></inf></formula>Mg<formula><inf><roman>1-c</roman></inf></formula>O solid solutions</title>

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ABSTRACT The Raman scattering by phonons and magnons was studied at room temperature in polycrystalline solid solutions NiMg1O and pure NiO. The experimental Raman spectrum of NiO consists of six well resolved bands, whose originis due to the disorder-induced one-phonon scattering (bands at 400 and 500 cm'), two-phonon scattering (bands at 750,900 and 1 100 cm) and two-magnon scattering (band at 1500 cm). In NiMg1O solid solutions, a relative increase ofone-phonon scattering is observed upon a dilution of nickel oxide by magnesium ions: at room temperature, the two-magnon band becomes invisible for c<O.7, whereas the two-phonon contribution disappears at c<O.5. Such behaviour isexplained by disorder-induced effect, caused by chemical substitution and off-centre displacement ofnickel ions.Keywords: NiMg1O solid solutions, NiO, Raman scattering, phonons, magnons 1. INTRODUCTION Diluted antiferromagnets represent an interesting class of materials, whose crystallographic structure is closely relatedto magnetic properties [1]. Recently, a correlation between long and short range order in solid solutions with a face-centred-cubic (fcc) magnetic sublattice has been reviewed for a number of zinc-blende and rock-salt type compounds[2]. In these systems, depending on the type ofthe host-lattice packing, the cation/anion radii ratio and the difference insubstituting ions size, the ordered on average crystal lattice experiences local distortions.NiMg1O system is a nice and very useful for theory example of diluted antiferromagnet. It forms a continuous seriesof solid solutions, whose magnetic properties vary with the composition from antiferromagnetic-like behaviour with the