Control of electromagnetic wave absorption properties in La-Co-Ti substituted M-type hexaferrite-epoxy composites

La-Co-Ti substituted Sr-hexaferrite, Sr0.906La0.094Fe11-2xCoxTixO19 (x = 0.8, 1.0, 1.2, 1.4) powder-epoxy (10 wt%) composites were fabricated for electromagnetic wave (EM) absorption application. Single M-type hexaferrite phase was confirmed by X-ray diffraction analysis for all the samples. Both saturation magnetization and coercivity of the composites decrease with increase of Co-Ti substitution x. Reflection loss (RL) of the hexaferrite powder-epoxy composites were calculated using their complex permittivity and permeability data. The EM absorbing frequency range is controlled by the substitution x because the ferromagnetic resonance (FMR) frequency of the samples is systematically varied following Snoek's limit law. The hexaferrite sample with x = 1.2 is suitable for use as an X band (8-12 GHz) radar absorber since RL <-10 dB is satisfied in the full X-band. Also, high EM absorbing performances in millimeter range, RL <-20 dB at 24 GHz (3 mm), and RL <-20 dB at 26.5 GHz (0.9 mm), could be achieved in the FMR-controlled La-Co-Ti substituted M-type hexaferrite-epoxy composite.