Synthesis and magnetic properties of hard/soft SrAl2Fe10O19/Fe(FeCo2) nanocomposites

Abstract

Abstract Hard/soft magnetic nanocomposites were synthesized with SrAl2Fe10O9 as hard and CoFe2 or Fe as soft magnetic phase. Al-substituted hexaferrite powder with 250 nm particle size is stable in Ar/5%H2 atmosphere at 315 °C, contrary to non-substituted hexaferrite. Annealing at T > 400 °C under these conditions leads to formation of Fe metal besides remaining hexaferrite phase. Such nanocomposites exhibit hysteresis loops with increased Ms. Alternative routes to synthesize nanocomposites were also explored. A mixture of hexaferrite and nanosize CoFe2O4 particles was annealed at 315 °C in Ar/5%H2 atmosphere. The spinel ferrite particles were reduced to CoFe2 alloy. Alternatively, soft iron nanoparticles were deposited onto the Al-substituted hexaferrite particles via a sodium borohydride reaction. Annealing at 315 °C in Ar/5%H2 gives a hexaferrite/Fe composite powder. Room temperature hysteresis loops, however, exhibit a multiple-phase reversal behavior.