We have measured the relaxation of the initial magnetic permeability after sample demagnetization, in the temperature range 80 K < T <420 K, in polycrystalline barium hexaferrites with a Ba : Fe ratio in the initial composition of 1: 18 corresponding to stoichiometric W phase. The materials were sintered under different temperature and oxygen pressure conditions. The results represented by isochronal curves show the existence of up to four relaxation processes. Additional thermo-gravimetric and X-ray diffraction studies reveal the successive formation of M, X, and W hexagonal phases with the increase of the sintering temperature. In this framework, we ascribe the relaxation processes to the progressive increase of ferrous cations in the different sites within the hexagonal lattice.
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