Semiconductivity in Ni1+xMnxFe2-2xO4 ferrites

Abstract The DC electrical resistivity ρ DC , thermoelectric power α , drift mobility μ D of electric charge carriers and initial magnetic permeability μ i were experimentally studied as a function of temperature T and composition x for a series of Ni 1+ x Mn x Fe 2−2 x O 4 ferrite samples prepared using the usual ceramic technique. The experimental results show that, ρ DC decreases while μ D increases on increasing the temperature. The magnetic permeability μ i increases as the temperature increases showing two peaks, the first is the Curie temperature T c while the second is below room temperature (for samples with x =0.1, 0.2 and 0.3). ρ DC , μ i , activation energies (for electric conduction E p in paramagnetic and E f in ferrimagnetic region; and E H for hopping) increase on increasing Ni 2+ and Mn 4+ ions substitution to reach maximum at x =0.3 and start to decrease for x >0.3. The activation energy E p is higher than E f . The positive sign of α for Ni 1.5 Mn 0.5 Fe 1 O 4 sample and negative sign for all other samples indicate that both types of charge carriers are responsible for electric conduction (the majority are holes for x =0.5 and electrons for all other samples). The Curie temperature T c and thermoelectric power α decrease as Ni 2+ and Mn 4+ ion substitution increases. The studied Ni 1+ x Mn x Fe 2−2 x O 4 ferrite samples have the magnetic semiconductor behavior. The small values of μ D (from 10 −10 to 10 −5  cm 2  V −2  s −1 ) and the strong temperature dependence of μ D confirm that the hopping conduction mechanism is dominant.