The ac conductivity and dielectric properties of four composites prepared
by mixing Mn_0.8-xMg_xZn_0.2Fe2O₄ (x = 0, 0.4) with polystyrene (30% wt. and 45%
wt.), were investigated as a function of frequency over a limited range of
temperature – to avoid melting of polystyrene - by using a complex impedance
technique. The ac conductivity shows the expected increase with increasing
frequency. The conductivity shows an interesting change in behavior from an
NTC thermistor behavior to a semiconductor like behavior. This suggests
further studies to explore new applications. Moreover, the dielectric constant
and the dielectric loss tangent (tan δ) have low values suggesting that the
studied composites may be good candidates for some practical applications that
require minimization of eddy currents.