Nanocrystalline oxide zinc materials studied by the Mossbauer effect, mu SR and neutron diffraction

ZnO and ZnFe2O4 were investigated in nanocrystalline form using various hyp erfine techniques in conjunction with neutron diffraction and bulk magnetic measurements. For the zinc oxide, the main interest was the influence of t he nanocrystalline state on lattice dynamics and on the local symmetry of t he Zn atom as reflected in its quadrupolar coupling, employing the high-res olution Mossbauer resonance of Zn-67. Measurements were carried out on nano crystalline materials with particle sizes between 4 and 25 nm. It was found that the asymmetry parameter increases drastically from eta = 0 in ZnO sin gle crystals to eta approximate to 0.5 in nanostructured material, indicati ng an off-axis displacement of either Zn or O atoms in finite size grains. The dependences of the Lamb-Mossbauer 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 ques tion of changes in the magnetic properties stood in the foreground. Using t he combination of techniques mentioned, the magnetic behavior of nanocrysta lline ZnFe2O4, which had an average particle size of about 9 nm was compare d 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.