Synthesis and magnetic properties of SrFe12−x−yAlxCoyO19 nanocomposites prepared via autocombustion technique

SrFe12−x−yAlxCoyO19 (x = 1.0-4.0, and y = 0.0-2.0) polycrystalline samples were prepared via autocombustion method and analyzed with respect to their structural and magnetic characteristics. The possibility of simultaneous substitution of Fe3+ by Al3+ and Co2+ was verified for low substitution degrees and it was established that single-phase Al3+-Co2+ substituted hexaferrites can only be obtained up to a maximum substitution of y < 1. A secondary soft magnetic phase CoFe2O4 segregated at higher degree of Co2+ substation (y ⩾ 1). The room temperature (300 K) magnetic parameters derived from hysteresis loops show enhancement in saturation magnetization and concomitant reduction in coercivity values of SrFe12−x−yAlxCoyO19 with the increase in cobalt content. The preferential site occupancy of substituted Co2+ and Al3+ ions resulted in a rapid decline in anisotropy field. Smooth hysteresis curves and increased Mr values with the Co2+ content indicate presence of exchange coupling between magnetic-hard and soft phases of the SrFe12−x−yAlxCoyO19 composite. A reduction in Curie temperature of the composite was observed with Co2+ substitution due to decrease in the strength and number of superexchange interactions between Fe3+ sites. As coercivity, remanence and saturation magnetization values could be controlled with the adequate ratio of Al3+ and Co2+ ions, the SrFe12−x−yAlxCoyO19 compound offers rich choice of using it as hard or soft-magnetic material.