Fabrication and exchange-spring properties of SrFe12O19@Fe3O4 nanocomposites with core-shell structure

Abstract

SrFe12O19@Fe3O4 nanocomposites with core–shell structure were synthesized by combining sol–gel and hydrothermal methods. The phase composition, surface morphology, and magnetic properties of the nanocomposites were investigated using X-ray powder diffraction, scanning electron microscopy, Raman spectroscopy and vibrating sample magnetometer. Findings show that the samples comprise two phases and that Fe3O4 particles are coated on the SrFe12O19 particles surface. The average particle size of SrFe12O19 core particles increases from 80 nm to 120 nm as the calcination temperature increased from 850 °C to 950 °C for 2 and 5 h. The coercivity of the SrFe12O19@Fe3O4 core–shell nanocomposites is smaller than that of the core SrFe12O19 nanoparticles. The hysteresis loops for the SrFe12O19@Fe3O4 nanocomposite particles shows a typical “bee waist”. The variations in coercivity, saturation magnetization and anisotropy constant of the core–shell nanocomposite samples are attributed to the architecture, phase composition of nanocomposite particles and the fundamental magnetization mechanism as well as the degree of exchange coupling between two magnetic phases.