Computational and experimental study on cation distribution of Cobalt substituted barium hexaferrites BaFe12−xCoxO19 (x = 0, 0.3, 0.6, 0.9) for circulator applications

•Cobalt substituted M-type hexaferrite sufficiently lower the magnetic anisotropy field while maintaining the saturation.•First-principles method is used to calculate the lattice parameter and substitution energy. The site preference is given.•A candidate material for K-band circulator is presented. The anisotropic BaFe12−xCoxO19 (x = 0, 0.3, 0.6, 0.9) (BFCO) samples were synthesized. We investigated the crystal structure, microstructure, and magnetic properties of BFCO. And the potential application value at millimeter waveband was discussed. The magnetic anisotropy field is successfully decrease from 17 kOe to 10 kOe by substituting Cobalt, which lower the Ferromagnetic resonance frequency and benefit for extending the bandwidth for the circulator. With the cobalt substitution, the saturation inevitably decreases from 60 emu/g to 45 emu/g. The site preference of cobalt in five crystallographically inequivalent Fe ions was calculated using software castep. The influence of site preference on lattice parameters and magnetic saturation was calculated and discussed. The result show cobalt mainly sites 2a and 12k position.