Evolution of microstructure and magnetic properties from amorphous Fe3O4/SiO2 nanocomposite

Abstract

Amorphous Fe3O4/SiO2 composite particles have been synthesized by using a one-pot sol-gel route. The evolution of Fe3O4 nanoparticles from the amorphous matrix on annealing temperatures up to 600 °C is identified through structural and vibrational mode studies. Electron microscopy measurements confirm that particles of 2–4 nm are embedded in the SiO2 matrix. The detailed analysis of temperature and field dependent magnetization data shows that a weak magnetic ground state of the as-prepared sample develops into a single domain state on annealing at 600 °C. Annealed samples exhibit higher magnetization values of ∼27 emu/g and coercivity of ∼1927 Oe at temperature of 2.5 K yet negligible spontaneous magnetization, suggesting short range magnetic order. A suitable distribution model with single domain particle assemblies is employed to analyze the particle size and moment distribution. From the analysis of M-T and M-H data it is found that interacting and non-interacting SPM models explain the data in different tampretaure ranges. We show magnetic interactions and anisotropy can be effectively controlled by the size and interparticle interactions of Fe3O4 nanoparticles. These particles are useful for the design of thermal seeds for magnetic hyperthermia.