Multiresonance Microwave Absorption in Ti–Mn Substituted Barium Hexaferrite Composites

Ti–Mn substituted Ba(TiMn) _x Fe _12-2x O ₁₉ hexaferrite randomly oriented composites were obtained by conventional ceramic synthesis. At zero applied magnetic field, in its polycrystalline powder form, this ferrimagnetic compound exhibits a multipeak permeability spectrum with two high-frequency resonances that converge under the action of an external magnetic field. We conduct a broad-band ferromagnetic resonances characterization of this system under an applied magnetic field between 0 and 2 T and integrate the results with micromagnetic simulations to investigate the presence of high-frequency resonating magnetic domains contingent upon the sample's microstructure. Simulations show that magnetic domains separated by domain walls upon each magnetic particle are responsible for the multipeak resonance in the Ka-band. By combining the simulated spectra with an effective medium theory accounting for the dilution effect of the dielectric matrix, we reproduce the zero-field permeability spectra.