Effect of annealing temperature on the structural and magnetic properties of CTAB-capped SrFe12O19 platelets

Abstract

The use of surfactant such as cetyl-trimethyl ammonium bromide (CTAB) in producing highly coercive SrFe12O19 platelets is presented in this study. The synthesis of SrFe12O19 was accomplished by co-precipitation in presence of 1wt% CTAB. The CTAB-coated precipitant thus obtained was subjected to annealing at different temperatures: 700, 800, 900 and 1000°C. The annealed counterparts were characterized with respect to their structural and magnetic properties and the results are compared with that of those processed without CTAB. Thermogravimetry analysis was employed to study the thermo-chemical behavior for the SrFe12O19 samples. The evolution of crystalline phases as a function of annealing temperature was studied using x-ray diffraction. For the SrFe12O19 samples without CTAB, formation of α-Fe2O3 secondary phases are noticed at annealing temperatures of 700 and 800°C; while such a secondary phase formation is not evident for the CTAB-capped SrFe12O19. Fourier transform infrared spectroscopy of the samples annealed at 1000°C showed deformation in the structure due to the splitting of the bands. Both morphology and composition of the samples were examined by a field-emission scanning electron microscope attached with energy dispersive x-ray analysis. The morphology of CTAB-capped SrFe12O19 samples showed the presence of hexagonal platelets at higher annealing temperatures. The magnetic parameters such as saturation magnetization, MS and coercivity, HC were evaluated from the magnetic hysteresis loops obtained by vibrating sample magnetometer. Maximum values of HC (6.3kOe) and MS (42.7emu/g) were obtained for the CTAB-capped SrFe12O19 samples annealed at 900°C. The possible mechanism on the formation of M-type hexagonal phase with platelet morphology using minimal amount of CTAB (1wt%) in achieving high the HC values for the SrFe12O19 is discussed.