M-type strontium hexaferrites with substitution of Fe3+ by Al3+, according to the formula SrAlxFe12-xO19 (x=0, 1, 2, 3, 4, 6, 8, 10), are prepared by the sol-gel auto-combustion method. Influences of the substituted amount of Al3+ on structure and magnetic properties of SrAlxFe12-xO19 compounds have systematically been investigated by XRD, TEM and VSM. X-ray diffraction shows that the samples are single M-type hexagonal ferrites. Because of the resemblance of Al3+ ionic radii with Fe3+ the two ions are easily replaced at any substitution ratio without changing the crystal structure. The materials show structural and morphology changes upon replacement of iron by aluminum. A shift in peak position to larger angles shown by XRD is observable with increasing aluminum doping. The values of Ms, Mr and Hc decrease with the addition of Al content but there is an exception for x=3 when Hc=8.9 KOe

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