A study of magnetic ordering in diluted antiferromagnet CoxZn1-xO (0.75 LT = x LT = 1)
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In order to study the influence of the magnetic ions dilution on the crystal and magnetic structure of polycrystalline CoxZn1-xO (x = 1, 0.90, 0.83, 0.75) samples we have performed neutron-diffraction experiments at several temperatures in the 10-295 K range. Magnetic transition temperatures were determined by magnetic susceptibility measurements over the 50-350 K temperature interval. The Rietveld refinements of the neutron data for all samples show that lowering of the crystal symmetry from cubic in the paramagnetic region to monoclinic in the magnetically ordered state occurs. It is found that the magnetic unit cell is double the monoclinic crystal cell along the c-axis, which points to the onset of antiferromagnetic ordering along that axis. Magnetic ordering of CoO is preserved in all the samples despite the magnetic dilution. This finding is confirmed by comparing the variation of magnetic moments with temperature for all samples, as well as by the concentration dependence of the... reduced Neel temperatures t = T-N(x)/T-N(1). The exchange interaction between Co2+ ions was found to be of the Heisenberg type. (C) 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.