An approach to the magnetic disaccommodation in Ti-substituted Ba–W hexaferrites

The relaxation of the initial permeability has been measured in polycrystalline Ti-doped Ba–W hexaferrites with nominal composition $BaTixFe18−xO27,$ with x ranging among $x=0$ and 0.3. The samples have been sintered at different temperatures in the $1250 °C<T<1350 °C$ range in a reducing $CO2$ atmosphere and rapidly quenched to promote the presence of crystal vacancies. X-ray diffraction spectra reveal the presence of hexaferrite as main phase. In the temperature range between 80 and 500 K, the time decay of the initial permeability after sample demagnetization has been plotted by means of isochronal curves. The isochronal disaccommodation spectra show an increase in the amplitude of the different disaccommodation peaks in substituted samples regarding pure Ba–W hexaferrites. These peaks are centered at 180, 300, and 380 K and they are related to the presence of both ferrous cations and lattice vacancies. The increase of the disaccommodation maxima in Ti-substituted hexaferrites is ascribed to the additional amount of ferrous cations induced by the presence of Ti cations, in order to maintain electrical neutrality. On the other hand, the isochronal spectrum in pure Ba–W shows another relaxation peak at 240 K which almost disappears in substituted hexaferrites, even with the lowest Ti doping analyzed. This behavior is explained in terms of the increasing hindrance to the mechanisms responsible for this ionic relaxation process, owing to the site occupation by the nonmagnetic Ti cations within the hexagonal structure.