Electrical properties and cation migration in manganese ferrites II. Time effects

A careful investigation of the time dependences of the electrical resistivity in two single crystals of MnFe₂O₄ at fixed temperatures in the 300–420 °C range showed that the changes are due to the migration of cations between the tetrahedral and the octahedral sites of the spinel lattice. The migration of cations can be described as a diffusion process resulting in the equilibrium distribution characteristic for a given temperature. Time constants involved in the diffusion strongly depend on temperature with the activation energyε=2.5 eV. The importance of a well defined cooling rate through the 600-400 °C temperature region is pointed out if ferrites with definite inversion degrees are needed.