Semiconductivity in Ni1+xMnxFe2-2xO4 ferrites

The DC electrical resistivity rho(DC), thermoelectric power alpha, drift mo bility mu(D) of electric charge carriers and initial magnetic permeability mu(i) were experimentally studied as a function of temperature T and compos ition x for a series of Ni1+xMnxFe2-2xO4 ferrite samples prepared using the usual ceramic technique. The experimental results show that, rho(DC) decre ases while mu(D) increases on increasing the temperature. The magnetic perm eability mu(1) increases as the temperature increases showing two peaks, th e first is the Curie temperature T, while the second is below room temperat ure (for samples with x = 0.1, 0.2 and 0.3). rho(DC), mu(i), activation ene rgies (for electric conduction E-p in paramagnetic and E-f in ferrimagnetic region; and E-H for hopping) increase on increasing Ni2+ and Mn4+ ions sub stitution to reach maximum at x = 0.3 and start to decrease for x > 0.3. Th e activation energy E-p is higher than E-f. The positive sign of a for Ni1. 5Mn0.5Fe1O4 sample and negative sign for all other samples indicate that bo th types of charge carriers are responsible for electric conduction (the ma jority are holes for x = 0.5 and electrons for all other samples). The Curi e temperature T-c and thermoelectric power as decrease as Ni2+ and Mn4+ ion substitution increases. The studied Ni1+xMnxFe2-2xO4 ferrite samples have the magnetic semiconductor behavior. The small values of mu(D), (from 10(-1 0) to 10(-5) cm(2) V-2 s(-1)) and the strong temperature dependence of mu(D ) confirm that the hopping conduction mechanism is dominant. (C) 1999 Elsev ier Science B.V. All rights reserved.