Electronic structure, and magnetic and microwave absorption properties of Co-doped SrFe12O19 hexaferrites

The crystalline and electronic structures and the magnetic and microwave absorption (MWA) properties of SrFe12-xCoxO19 (x = 0-1) hexaferrites have been studied. The structural analyses indicate that an increase in Co content (x) from 0 to 0.2 enhances slightly the lattice constant c while a reduces, proving Jahn-Teller distortions. A further increase in x causes a gradual decrease of both a and c. The electronic structure study indicates the copresence of Fe2+ and Fe3+ in some doped compounds while Co is stable with the oxidation state 2+. Magnetization measurements for the doped compounds reveal a gradual enhancement of the saturation magnetization (M-s) from similar to 46.7 emu/g for x = 0.1 to 51.7 emu/g for x = 1. Meanwhile, the coercivity (H-c) tends to decrease from similar to 3.2 kOe for x = 0.1 to 1.7 kOe for x = 1. Such changes are correlated to a partial replacement of Co2+ for Fe-2+,Fe-3+ in preferable sites. Investigating the MWA properties in the frequency range f = 1-12 GHz, we have found the compounds with x = 0.4 and 1 showing good MWA possibility. The best MWA performance corresponds to x = 0.4 with the thickness of 2 mm. Its minimum RL value obtained at f = 10.9 GHz is about - 45.2 dB, meaning > 99.99% microwaves being absorbed. The results reflect that the Co doping improved the magnetic and MWA properties of SrCoxFe12-xO19.