Characteristic length scales of nanosize zinc ferrite

Nanosize zinc ferrite samples with an average particle size of 6–65 nm were prepared by a new chemical reaction involving nitrates of Zn and Fe and investigated for magnetic behaviour and defect structure. The sample with an average particle size of 6 nm has considerable inversion in cation distribution as shown by its hysteresis loop and increased magnetization. Mössbauer spectroscopy gives a single doublet for all the samples. Mössbauer parameters like quadrupole splitting and linewidth change sharply as the average particle size increases from 6 to 7 nm and then afterwards the changes are slow. The total Mössbauer absorption, on the average, increases with increase in particle size, the change from 6 to 65 nm being by a factor of 3. Positron parameters too change sharply as the particle size varies. The changes are related to inversion of the cation distribution, agglomeration of particles and annihilation at the surface and in the interior. The picture that emerges from the lifetime studies and supported by Mössbauer spectroscopy and magnetization studies suggests that there are at least two characteristic particle size length scales for nanosize ZnFe2O4 particles prepared by the nitrate route.