Structure and magnetic properties of Zn ferrite nanoparticles

A series of ZnxFe3-xO4(x=,0.1,0.3,0.4,0.4,0.6,0.70) nanoparticles prepared by hydrothermal method are studied by use of transmission electron microscope, X-ray diffraction, vibrating sample magnetometer, superconducting quantum interference device magnetometer and Mossbauer spectrometer. All samples present a spinel structure. The lattice constant increases with the increase in the Zn content while the grain size decreases from 18 nm to 9 nm. Moreover, the saturation magnetization at 5 K and 293 K increases initially when x,0.40 and subsequently decreases when x > 0.40.At room temperature, Mossbauer spectra exhibit a change from a well-defined sextet spectrum to a doublet spectrum as the Zn content increases. The doublet spectrum begins to appear when x=0.6, while it begins when x=0.80 for the bulk materials. The results of magnetization and Curie temperature measurements indicate that the doublet spectrum is due to the surperparamagnetic state of the nanoparticles. Furthermore, the relationship between the hyperfine field variation and the cation distribution is discussed. The variation of magnetic properties is interpreted by the three-sublattice Yafet-Kittel (Y-K) model.