A series of polycrystalline Ba Zn2-x Mgx Fe16 O27 W-type hexagonal
ferrite; (x = 0.0,0.4,0.8,1.2,1.6 and 2) were prepared by using the conventional
ceramic method. The dielectric constant (ε′) and the dielectric loss tangent
(tan δ ) were determined as functions of frequency, temperature and
composition. The frequency dependence of the dielectric constant was found to
exhibit two types of behaviour: the usual dispersion at low temperatures and an
abnormal behaviour at relatively high temperatures which could be explained
on the basis of Rezlescu and Rezlescu assumption, which attributes this
abnormal behaviour to a collective contribution of two types of charge carriers
to the polarization.