Low-temperature sintering and magnetic properties of Sc- and In-substituted M-type hexagonal barium ferrites for microwave applications

Partial substitution of Fe3+ by Sc3+ or In3+ in M-type ferrite is an effective method to tailor their anisotropy field and resonance frequency. BaMexFe12-xO19 with Me = Sc and In (0 ≤ x ≤ 2) was synthesized by the mixed-oxide route. XRD revealed a continuous increase of the hexagonal lattice parameters with substitution rate x. Both, the saturation magnetization and coercivity at room temperature are reduced with x. The ferromagnetic resonance frequency decreases from 48 GHz at x = 0 to 30 GHz at x = 0.5 for Sc-substituted ferrites. For In-substitution, a smaller reduction of the resonance frequency with x is observed, e.g. to 37 GHz at x = 0.5. Addition of BBSZ glass allows sintering at 900 °C. Low-temperature fired samples exhibit ferromagnetic resonance at the same frequencies and represent promising materials for self-biased microwave components for integration into LTCC multilayer modules.