Magnetic Study of M-type Co-Ti Doped Strontium Hexaferrite Nanocrystalline Particles

Abstract

The effects of Co-Ti ions substituting Fe3+ ions in strontium hexaferrite nanoparticles synthesized using ball-milling technique were investigated. X-ray diffraction patterns of SrFe12-2xCoxTixO19 (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) demonstrated standard SrFe12O19 patterns with space group P63/mmc. The phase purity and the valence state of each ion were examined using X-ray photoelectron spectroscopy. The results indicated a Ti4+ valence state and a coexistence of 2 + and 3 + valence states for Fe and Co. An obvious irreversibility between the zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves was observed below 300 K. The broad peaks in the ZFC curves were attributed to the movement of magnetic domains at temperature (TM). Magnetization hysteresis loops at discrete temperatures between 4 and 300 K showed a ferromagnetic behavior, with high coercive fields and large saturation magnetizations. The change of the saturation magnetization with increasing x revealed spin reorientation behavior at x ≥ 0.4 and remained relatively high for practical applications. The first anisotropy constant decreased with the increase of temperature. With Co-Ti substitution, it remained almost constant up to x = 0.4, and then decreased almost linearly at higher Co-Ti concentrations. Furthermore, the coercive field decreased with increasing x, reaching values suitable for high-density magnetic recording at 300 K in the substitution range 0.4 ≤ x ≤ 0.8.