Iron oxide nanocomposite magnets produced by partial reduction of strontium hexaferrite

¹ Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI-20014, Finland
² University of Turku Graduate School (UTUGS), University of Turku, FI-20014, Finland

^a Corresponding author: jussi.tikkanen@utu.fi

Published online: 3 July 2014

Abstract

Isotropic bulk nanocomposite permanent magnets were produced with strontium hexaferrite, SrO·6Fe₂O₃, and magnetite, Fe₃O₄, as the magnetically hard and soft components. A novels synthesis scheme based on the partial reduction of SrO·6Fe₂O₃ was employed. In two parallel experiments, nano- and microcrystalline SrO·6Fe₂O₃ particles were compacted into pellets along with a controlled, understoichiometric amount of potato starch as a reducing agent. The pellets were then sintered in a passive atmosphere. Based on XRD and room temperature magnetic hysteresis measurements, it was concluded that a fraction of the SrO·6Fe₂O₃ input material had been reduced into Fe₃O₄. In comparison with pure SrO·6Fe₂O₃ control pellets, these composites exhibited maximum energy product increases in excess of 5 % due to remanence boosting. The improvement of magnetic properties was attributed to an efficient exchange spring coupling between the magnetic phases. Interestingly, as the synthesis scheme also worked for microcrystalline SrO·6Fe₂O₃ , the method could presumably be adapted to yield crystallographically oriented bulk nanocomposite magnets.