Mössbauer Effect Study of Superparamagnetic Behavior of ZnFe2O4 Nanoparticles Formed in ZnO Doped with Fe2O3

Abstract

Superparamagnetic behavior of ZnFe2O4 nanoparticles formed by doping ZnO with various content of α‐Fe2O3 is investigated by 57Fe Mössbauer spectroscopy measurements performed in a temperature range from 300 to 10 K. The nanoparticles were obtained by the hydrothermal synthesis with Fe2O3 doping ranging from 30 to 70 wt.%. The results are compared with the ZnO sample doped with 60% Fe2O3, prepared by the calcination method. At room temperature the Mössbauer spectra of all samples consist of a nonmagnetic component characteristic for Fe3+ ions in ZnFe2O4 spinel structure. Low temperature Mössbauer measurements of hydrothermally synthesized nanoparticles reveal appearance of a magnetically ordered spectral component at about 120 K for the sample doped with 70% Fe2O3 and below 30 K for all other compositions. The spectral contribution of the magnetic component increases gradually at decreasing temperature at the expense of the nonmagnetic component, indicating superparamagnetic relaxation of ZnFe2O4 nanoparticles. It is concluded that the spinel nanoparticles are significantly smaller in the samples obtained by the hydrothermal method than by the calcination one. The blocking temperature is found to decrease with decreasing content of Fe2O3 doping during preparation of the nanoparticles.