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

The relaxation of the initial permeability has been measured in polycrystal line Ti-doped Ba-W hexaferrites with nominal composition BaTixFe18-xO27, wi th x ranging among x=0 and 0.3. The samples have been sintered at different temperatures in the 1250 degrees C < T < 1350 degrees C range in a reducin g CO2 atmosphere and rapidly quenched to promote the presence of crystal va cancies. X-ray diffraction spectra reveal the presence of hexaferrite as ma in phase. In the temperature range between 80 and 500 K, the time decay of the initial permeability after sample demagnetization has been plotted by m eans of isochronal curves. The isochronal disaccommodation spectra show an increase in the amplitude of the different disaccommodation peaks in substi tuted 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 c ations and lattice vacancies. The increase of the disaccommodation maxima i n Ti-substituted hexaferrites is ascribed to the additional amount of ferro us cations induced by the presence of Ti cations, in order to maintain elec trical neutrality. On the other hand, the isochronal spectrum in pure Ba-W shows another relaxation peak at 240 K which almost disappears in substitut ed hexaferrites, even with the lowest Ti doping analyzed. This behavior is explained in terms of the increasing hindrance to the mechanisms responsibl e for this ionic relaxation process, owing to the site occupation by the no nmagnetic Ti cations within the hexagonal structure. (C) 2000 American Inst itute of Physics. [S0021-8979(00)23508-1].