Electronic structure and magnetic properties of Ba1-xSrxCoFe11O19 hexaferrites

We have prepared Ba1-xSrxCoFe11O19 hexaferrite nanoparticles (NPs) by using a co-precipitation method. The crystal/electronic structures and magnetic properties were then studied. Results revealed that all Ba1-xSrxCoFe11O19 NPs with particle sizes of 100-300 nm crystallized in a hexagonal structure. Both the particle shape and the unit-cell parameters are changed when Sr content (x) increases. The analysis of the electronic structure based on the Fe and Co K-edge XAS spectra proved the oxidation states of Fe and Co to be 3 + and 2 + , respectively, which are stable versus an x change in Ba1-xSrxCoFe11O19. Local-structural studies also revealed the average bond length between Fe and O of 1.89-1.91 Å less changed by Sr doping. Though the electronic structures of Fe and Co were unchanged, the studies about the magnetic property demonstrated a strong dependence of Ms and Hc on Sr doping. While Ms decreases from 46.1 emu/g for x = 0-34.2 emu/g for x = 1, Hc tends to increase from 1630 Oe for x = 0 to ~ 2200 Oe for x = 0.5, but slightly decreases to 2040 Oe for x = 1. We think that the addition of the exchange interaction between Fe3+ and Co2+ ions and the changes of local-geometric structures and microstructures influenced directly Ms and Hc of NPs.