Size-dependent magnetic properties of Mn_0.5Zn_0.5Fe₂O₄ nanoparticles in SiO₂ matrix

Mn_0.5Zn_0.5Fe₂O₄ ferrite nanoparticles (≪100 nm) in SiO₂ matrix have been prepared by the sol-gel method. The particle size was varied by changing the duration of heat treatment above crystallization temperature. An x-ray diffraction study indicates the presence of single-phase spinel ferrite in the sample. The particle size was estimated by the x-ray diffraction method as well as from the micrograph taken by a transmission electron microscope. The magnetic properties of the samples were studied by a vibrating sample magnetometer. The samples show superparamagnetic behavior when the particle size is below 20 nm, which is confirmed by Mössbauer spectroscopy measurements. The average particle size in the superparamagnetic state was also estimated from the low-field magnetization measurement by considering the samples as consisting of noninteracting single domain particles. © 2002 American Institute of Physics.