Abstract
The BaCuFe 17O 27 W-type hexagonal ferrite is ferrimagnetic ( T c = 485° C) with a room temperature magnetization σ = 74.5 emu⧸ g. During the annealing treatment, an oxidation phenomenon occurs on the monovalent copper; we study 3 samples corresponding to different grain sizes (# 50, 14 and 2 μm, respectively) in the (20–1330°C) annealing temperature range. The post annealing room temperature magnetization variation shows the mechanism to be located on the surface of the grains with a saturation effect which is dependent of the surface state together with the temperature. By means of neutron diffraction on powder samples incompletely oxidized, we deduce an intermediate valency of copper which confirms the oxidation phenomenon; we also locate the vacancies and copper cations among the seven sublattices of the W-type structure: they lie in the 6g octohedral and 4e tetrahedral sites.
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