Structural and magnetic properties of soft/hard NiFe 2 O 4 @SrCo 0.2 Fe 11.8 O 19 core/shell composite prepared by the ball-milling-assisted ceramic process

Soft/hard xNiFe2O4@(1−x)SrCo0.2Fe11.8O19 (x = 0.00, 0.15, 0.30, and 0.45) core/shell magnetic composites have been synthesized by the ball-milling-assisted ceramic process. The analysis of XRD indicates the coexistence of NiFe2O4 and SrCo0.2Fe11.8O19. The core/shell structure of the composite sample has been confirmed by Fourier transform infrared spectra. When xNiFe2O4@(1−x)SrCo0.2Fe11.8O19 precursor is calcined at 900 °C, the crystallite size of obtained core/shell composites is between 28.3 and 46.6 nm in core NiFe2O4 and between 59.2 and 74.5 nm in shell SrCo0.2Fe11.8O19. Magnetic characterization indicates that specific saturation magnetization of xNiFe2O4@(1−x)SrCo0.2Fe11.8O19 composites increases with the increase in calcination temperature, and decreases with the increase in mass ratio of soft to hard magnetic phase. Compared with bare SrCo0.2Fe11.8O19 calcined at 950 °C, the specific saturation magnetization of xNiFe2O4@(1−x)SrCo0.2Fe11.8O19 composites is decreased and coercivity is increased. This is attributed to the exchange–coupling interaction between the hard and soft phases due to formation of core/shell structure. Besides, remanence and magnetic moment of xNiFe2O4@(1−x)SrCo0.2Fe11.8O19 composites decrease with the increase in NiFe2O4 content. The xNiFe2O4@(1−x)SrCo0.2Fe11.8O19 composites have higher squareness (Mr/Ms) value compared with the bare SrCo0.2Fe11.8O19, which is useful for high-density magnetic recording and enhanced memory storage.