Magnetic aftereffects in manganese ferrites

The magnetic aftereffect in MnxFe3-x-ΔO4 is investigated as a function of the Mn concentration (0 < x < 1.0) and the cation vacancy concentration (10−4 < Δ < 5×10−2) in the temperature range between 80 and 530 K. Well defined relaxation processes are observed at 300 (III), 425 (II), and 530 K (I). By means of computer analysis it can be demonstrated that the peak at 425 K, being known so far only as one relaxation process, actually can be separated into two different processes, denoted henceforth by IIa and II. Process II proves to be a simple Debye process with the following activation parameters: 1.0 eV < < QII < 1.3 eV; 10−13 s < τ0, II < 2 τ0,II < 2×10−12 s, corresponding to increasing Mn concentrations. The increase of the activation energy in Mn-rich ferrites is explained by the formation of tightly bound Mn3+Fe2+-pairs due to a Jahn-Teller-induced anisotropy of Mn3+ ions. Process IIa is attributed to long-range diffusion of Mn ions in the spinel lattice by means of vacancies on octahedral sites.