Positron annihilation and Mossbauer spectroscopic studies of In3+ substitution effects in bulk and nanocrystalline MgMn0.1Fe1.9-xInxO4

Positron lifetime and Mossbauer spectroscopic studies were carried out on MgMn0.1Fe1.9-xInxO4 spinel ferrite samples, both in bulk and nanocrystalline forms. The positron lifetimes at various substituted In3+ concentrations suggested changes in the predominant positron trapping sites. In the initial stage of substitution when In3+ ions were supposed to migrate to tetrahedral sites, many of these sites were left as vacancies and positrons were trapped in them. At higher concentrations of In3+, similar situation arises in the case of the octahedral sites. The same qualitative trend is observed when the sample is ball-milled to nanometre dimensions. Quantitatively, however, the measured positron lifetimes are larger than those for the bulk, signifying the annihilations at the grain surfaces and interfaces. From the Mossbauer studies, one observes changes in the electron density, electric field gradient and hyperfine field for nanoparticles in comparison to the bulk samples. (C) 2004 Elsevier B.V. All rights reserved.