Crystalline and electronic structure and magnetic properties of La-doped Ba3Co2Fe24O41 hexaferrites

Using solid-state reactions, we successfully synthesized Z-type hexaferrites of Ba3-xLaxCo2Fe24O41 (x = 0-0.5) with micro-particle sizes of 5-10 mu m. XRD analyses indicated that all of the samples were single phase belonging to the group of Z-type hexaferrites. The unit-cell parameters gradually decreased with increasing La-doping content (x). Electronic-structural analyses of the Fe and Co K-edges X-ray absorption spectra proved the oxidation states of Fe and Co in Ba3Co2Fe24O41 to be 3 + and 2 +, respectively. For Ba3-xLaxCo2Fe24O41 compounds, while the oxidation state of Co is stable, that of Fe is changed with the addition of a small amount of Fe2+ ions (besides pre-existing Fe3+ ions) when x changes. These factors directly influence M-s, H-c, and the ferromagnetic phase. Interestingly, we have found that the La doping enhances M-s and widens the ferromagnetic phase, while the soft-magnetic behavior remains stable. This demonstrates the application potential of Ba3-xLaxCo2Fe24O41 compounds in electromagnetic-wave shielding devices working at GHz frequencies.