Magnetic properties of solvothermally synthesized ZnFe₂O₄nanoparticles

Abstract

ZnFe2O4 nanoparticles with a mean size ranging from 3 nm to 10 nm, have been prepared using the solvothermal method. The TEM images reveal a narrow particle size distribution for all samples. Bulk magnetic measurements indicate superparamagnetic behaviour with a blocking temperature (TB) that increases from 10 K to 22 K upon increasing the particle size. At temperatures lower than TB the nanoparticles are in the "frozen" regime and the coercive field changes from 145 Oe to 220 Oe for nanoparticles with sizes from 3 nm to 10 nm. On heating, the Mössbauer spectroscopy data show a progressive crossover from a magnetic to a quadrupolar hyperfine interaction, with a blocking temperature coherent with that obtained from magnetization measurements. The spinel inversion parameter, which appears to be a function of the particle size, has been estimated from neutron diffraction experiments.