Composition and magnetic studies of ultrafine Al-substituted Sr hexaferrite particles prepared by citrate sol–gel method

Abstract

Ultrafine aluminum-substituted strontium hexaferrite particles have been prepared via citrate sol–gel route. Gels were synthesized with molar ratios [Al3+]:[Fe3+] of 0.4:11.6, 1:11, 1.5:10.5 and 2:10 and the ferrite particles were obtained by annealing the gels at 950°C for 2 and 24h. Electron energy dispersive X-ray spectroscopy (EDX) verified the presence of Al in the substituted samples. X-ray diffraction (XRD) confirmed the formation of the M-type hexaferrite phase in the samples with some indication of α-Fe2O3. Scanning electron microscope showed that the hexaferrite powder consists hexagonal crystals with average diameter Dav (80–186nm) that decreases with increasing Al content and increases with increasing annealing time. Magnetic properties were determined using a pulsed-field magnetometer and a vibrating sample magnetometer (VSM). The saturation magnetization at room temperature and the Curie temperature were found to decrease while the coercivity increases with increasing the Al content. The highest coercivity of 10.1kOe was achieved for the sample with the molar ratio [Al3+]:[Fe3+]=2:10 annealed for 24h. The influences of the particle size, composition and impurity on the magnetic properties were discussed.