Structure and magnetic properties of Al3+ substituted M-type SrLaCo hexaferrite

M-type hexagonal ferrites (SrFe12O19) have attracted much attention as a widely used permanent magnet. Many studies have been done to improve permanent magnetic properties. In particular, the formula of La-Co co-replaced Sr-Fe has achieved higher performance. However, no one has studied the influence of a small amount of Al ions on the above formula. In this study, the Al3+ ion substituted M-type Sr0.7La0.3Fe11.75.x-AlxCo0.25O19 (0 < x < 0.12) hexagonal ferrites were synthesized by solid state reaction. The crystalline structure was investigated by using X-ray diffraction (XRD) and the Rietveld refining method. The morphological of powder and magnetically oriented bulk were observed by scanning electron microscopy (SEM), and magnetic properties were measured by physical property measurement system-vibrating sample magnetometer (PPMS-VSM) techniques. The results show that a single M-type strontium ferrite was obtained with the Aluminum (Al) content (x) from 0 to 0.08, and the impure phase appeared when x was 0.12. The lattice parameters a and c both decreased with the increasing Al3+ content. SEM images indicate the hexagonal platelet-like particles and the size of the magnetic powders about 2-5 mu m, and the powders are easily arranged in one direction under a magnetic field. The saturation magnetization (M-s) of the hexaferrite decreased with the increase of x from 0 to 0.12, but coercivity (H-c) of the magnetic powders increased with Al3+ content (x) from 0 to 0.12.