Low temperature electric properties of magnetite Mn-ferrites

Electrical resistivity and thermoelectric power measurements have been made on single crystals of manganese ferrites, Mn_xFe_3-xO₄ (x=0, 0.5, 0.7, 0.8, 0.9, and 0.95) in the temperature range 10 K to 300 K. Below the Verwey transition T_v of magnetite, the thermoelectric power is strongly influenced by the oxygen nonstoichiometry of the samples whereas the resistivity exhibits hardly any dependence on the changes of the oxygen content. Starting from the lowest temperatures, the electrical properties are explained in terms of the impurity band, variable range hopping, small polaron band, and small polaron hopping conduction mechanisms where the long-range and the short-range orderings have to be taken into account.