Magnetic properties of zinc ferrite nanoparticles synthesized by hydrolysis in a polyol medium

Highly crystalline, nanometre sized ZnFe 2 O 4 particles with different diameters, 6.6 and 14.8 nm, were prepared by forced hydrolysis in a polyol medium. The DC magnetic properties exhibit a strong dependence on the particle size as a result of the unusual cation distribution. They clearly establish their superparamagnetic character at room temperature and the occurrence of ferrimagnetic or ferromagnetic ordering at low temperature. The magnetization is found to increase with grain size reduction. The 57 Fe Mössbauer spectra were recorded at 300 and 4.5 K. There is no evidence for the presence of the Fe 2+ charge state, confirming the perfect stoichiometry of the two samples. At 300 K, the Mössbauer spectra consist of doublets due to the superparamagnetic behaviour whereas at 4.5 K they reveal a magnetically blocked state. Mössbauer spectra at 10 K in an external 6 T magnetic field applied parallel to the direction of the gamma rays clearly show a close to collinear Néel-like ferrimagnetic ordering for the 6.6 nm particles and a canted Yafet–Kittel-like ferrimagnetic ordering for the 14.8 nm ones.