Structural and Magnetic Properties of Soft/Hard Mn0.6Zn0.4Fe2O4@Sr0.85Ba0.15Fe12O19 Core/Shell Composite Synthesized by the Ball-Milling-Assisted Ceramic Process

Abstract

Soft/hard xMn0.6Zn0.4Fe2O4@(1−x)Sr0.85Ba0.15Fe12O19 (x = 0.15, 0.30, and 0.45) core/shell magnetic composites have been synthesized by the two-step ball-milling-assisted ceramic process. The products are characterized by x-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), a vibrating sample magnetometer (VSM). The XRD analysis indicates the coexistence of ZnFe2O4 and SrFe12O19 phases. FT-IR results show that an Sr0.85Ba0.15Fe12O19 shell is on the surface of the Mn0.6Zn0.4Fe2O4 core. When Mn0.6Zn0.4Fe2O4@Sr0.85Ba0.15Fe12O19 precursor is calcined at 900°C, the crystallite size of obtained core/shell composites is between 33.50 ± 0.50 nm and 47.91 ± 0.72 nm in core Mn0.6Zn0.4Fe2O4 and between 59.34 ± 0.89 nm and 67.61 ± 1.01 nm in shell Sr0.85Ba0.15Fe12O19. Magnetic characterization indicates that the specific saturation magnetization of xMn0.6Zn0.4Fe2O4@(1−x)Sr0.85Ba0.15Fe12O19 composites decreases with the increase in mass ratio of soft-to-hard magnetic phases. Compared with bare Sr0.85Ba0.15Fe12O19 calcined at 950°C, the specific saturation magnetization of the composites is decreased and coercivity is markedly increased. This is attributed to the exchange-coupling interaction between the hard and soft magnetic phases due to formation of the core/shell structure. The 0.15Mn0.6Zn0.4Fe2O4@0.85Sr0.85Ba0.15Fe12O19 composite calcined at 700°C has higher squareness (Mr/Ms = 0.5401 ± 0.0065) and coercivity (4288.09 ± 42.88 Oe) values compared with the bare Sr0.85Ba0.15Fe12O19, which are useful for high-density magnetic recording and enhanced memory storage.