Multiple natural resonances broaden microwave absorption bandwidth of substituted M-type hexaferrites

BaFe 12–2 x (Mn 0.5 Co 0.5 Ti) x O 19 ( x  = 0, 0.5, 1.0, 2.0) powders were synthesized by a solid-state reaction (SSR) technique and its microwave absorption bandwidth was broadened by multiple magnetic resonances. The crystalline phases, microstructure, magnetic properties , and microwave (MW) absorption properties of substituted M-type barium hexaferrites (BaM, BaFe 12 O 19 ) were investigated. The refined X-ray diffraction (XRD) patterns and scanning electron microscope (SEM) images showed that all prepared samples consisted of single-phase flake shaped particles. With an increase of substitution x , the saturation magnetization ( M s ) and coercivity ( H c ) changed, resulting in a transition from hard magnetic to soft magnetic samples. The dielectric spectra and magnetic spectra of the substituted samples presented resonance at almost the same position, and multiple resonances of magnetic spectra were observed with an increase in the doping amount x , which enhanced the MW absorption and broadened the effective absorption bandwidth ( EAB ). For the x  = 0.5 sample, the minimum reflection loss ( RL min ) arrived −40.2 dB, and the EABs of RL <−10 dB and RL <−20 dB widened to 7.0 GHz and 4.2 GHz respectively, with a corresponding coating thickness of 2.3 mm. The energy dissipation mechanism of all substituted samples was dominated by a dielectric resonance and natural resonance, including the contribution of exchange resonance. The BaFe 11 (Mn 0.5 Co 0.5 Ti) 0.5 O 19 is therefore a desirable candidate for electromagnetic wave (EMW) absorber applications.