Permeability and permittivity spectra of substituted barium Ferrites BaFe12−x(Ti0.5Co0.5)xO19(x=0 to 5)

• We analyzed the permeability and permittivity spectra of BaFe12−x(Ti0.5Co0.5)xO19.
• Domain wall and spin resonance contributions were evaluated by the numerical analysis.
• The high permeability in the BaFe9(Ti0.5Co0.5)3O19 is attributed to domain wall resonance.
• Dielectric constant of BaFe12−x(Ti0.5Co0.5)xO19 is enhanced by the substitution.

Relative complex permeability and permittivity spectra of a series of Ti, Co-substituted sintered M-type barium hexaferrite BaFe12−x(Ti0.5Co0.5)xO19 (x=0–5) have been studied from RF to microwave range. As a phenomenological treatment, contribution of the domain wall vibration and the gyromagnetic spin rotation to the permeability spectrum was evaluated by the numerical curve fitting using the two types of permeability resonance formulae. In the low composition range of x=0 and 1, the frequency dispersion of permeability in RF range can be originated by the domain wall resonance where the gyromagnetic spin resonance gives small susceptibility and takes place in several tens GHz due to high uniaxial magnetic anisotropy. Low frequency permeability of BaFe12−x(Ti0.5Co0.5)xO19 increases with x and has a maximum at around x=3; the spin resonance frequency is considered to be decreased by the reduction of the uniaxial anisotropy. However, contribution of the spin susceptibility is not so large in the high permeability composition range; the domain wall susceptibility may be still dominant in the reduced magnetic anisotropy state at x=3. Complex permittivity spectra of BaFe12−x(Ti0.5Co0.5)xO19 indicate a relaxation type behavior in RF frequency range; permittivity increases with increasing (Ti0.5Co0.5) composition up to x=5.