Springer Online Journal Archives 1860-2000
Abstract ZnO and ZnFe2O4 were investigated in nanocrystalline form using various hyperfine techniques in conjunction with neutron diffraction and bulk magnetic measurements. For the zinc oxide, the main interest was the influence of the nanocrystalline state on lattice dynamics and on the local symmetry of the Zn atom as reflected in its quadrupolar coupling, employing the high-resolution Mössbauer resonance of 67Zn. Measurements were carried out on nanocrystalline materials with particle sizes between 4 and 25 nm. It was found that the asymmetry parameter increases drastically from η=0 in ZnO single crystals to η≈0.5 in nanostructured material, indicating an off-axis displacement of either Zn or O atoms in finite size grains. The dependences of the Lamb-Mössbauer factor on grain size and temperature are well described by a two-component model in which small crystallites are surrounded by a network of grain boundaries. For the zinc ferrite the question of changes in the magnetic properties stood in the foreground. Using the combination of techniques mentioned, the magnetic behavior of nanocrystalline ZnFe2O4, which had an average particle size of about 9 nm was compared to differently prepared crystalline samples. It was seen that the role of cation-site occupation, which changes substantially with nanocrystallinity, plays a decisive role for the magnetic properties.
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