Evolution of structure and magnetic properties in MnZn ferrite-silica nanocomposites fabricated by sol-gel method

摘要

We explore the influence of the silica matrix on size, spinel phase stability, and magnetic properties of MnZn ferrite. For this purpose, Mn_(0.6)Zn_(0.4)Fe_2O_4 (MZF) nanoparticles (NPs) dispersed in silica (SiO-2) matrix [MZF_(1-x)/(SiO_2)_xx = 0, 10, 30%] synthesized by one-pot sol-gel process. The evolution of a pure spinel phase is apparent from the as-prepared (AP) MZF/SiO_2 (30%) amorphous state on annealing in the temperature range 600-900°C in air, whereas the AP freestanding MZF NPs exhibit a secondary phase of α-Fe_2O_3 along with spinel structure in this temperature range. The crystallite size is 5 ± 1 nm for a 600°C annealed sample and increases to 10 ± 1 nm for a 900 °C annealed sample. From the detailed analysis of the temperature and magnetic field-dependent magnetization data, it is found that the AP sample exhibits weak magnetic behavior. However, annealed samples exhibit a maximum in zero-field-cooled magnetization at a certain temperature (T_p), which increases with the increase of annealing temperature. The M-H curves above T_p indicate the presence of superparamagnetic (SPM)-like behavior. From the present study, we show that the phase stability and magnetic properties of MZF/SiO_2 composites have improved compared to bare MZF NPs.