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Influence of chemical bonding on the spatial distribution of charge and magnetization densities in inorganic compounds

Electron density studies based on X-ray single crystal diffractometry have been made of the chromium (3+) ion in chromium sesquioxide (Cr2O3), and of the copper (2+) ion in the silicate mineral dioptase (Cu6Si6O18.6H2O). Neutron diffraction experiments have determined the antiferromagnetic structure and magnetization density in the latter material. Zero-field neutron polarimetry has determined the relation between the absolute antiferromagnetic configuration in chromium sesquioxide and the direction of an external magnetic field applied whilst the crystal is cooled through its Neel point. Studies of the electron and magnetization densities associated with the vanadium (3+) ion have been furthered by a high resolution neutron powder diffraction study of the structural phase transition at 110 K in the fluoride K5V3F14. Both the temperature dependence of the magnetic propagation vector K and the magnetic structure of manganese sulphate have been studied in the temperature range from 4.2 K to the Néel point. Major differences were found from the previously published values for the magnitude and direction of K, which does not appear to change in the temperature interval between 4 K and a revised Néel temperature of 12 K. It is concluded that the higher symmetry and the presence of a single independent manganese (2+) ion, rather than the three independent iron (3+) ions in triclinic iron vanadium oxide (FeVO4), prevent the moments from responding more freely to small, temperature-induced changes in the magnetic exchange coupling. Single crystals of new magnetic phases have been grown. The comparative investigations of charge and magnetization densities make a significant contribution to the relatively few studies in this field.

Reported by

Engineering and Physical Sciences Research Council
OX11 0QX Didcot
United Kingdom
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