Electrical conductivity of MnZn ferrite single crystals with a small number of Fe2+ ions

The electrical conductivity of Mna2+Znb2+Fec2+Fe23+O42- (0.52less than or equal toaless than or equal to0.72, 0.20less than or equal tobless than or equal to0.43, 0.0023less than or equal tocless than or equal to0.14) single crystals was measured in the temperature range of 80-300 K. Electrical conductivity increases monotonously with the concentration of Fe2+ ions. The activation energy for hopping conduction is 0.024-0.27eV and shows its minimum value in the vicinity of c=0.06. Due to low carrier mobility, a small polaron effect is expected to be important at c<0.06. In contrast, the high carrier mobility at c>0.06 suggests that the Coulomb interaction between carriers increases with the Fe2+ ion concentration. Polaron binding energy and Coulmb interaction are considered to result in additional activation energy for hopping conduction. Thus, the electrical conduction mechanism of ferrite is understood as the result of competition between the polaron effect and electron-electron interactions. (C) 2004 Elsevier B.V. All rights reserved.