Interaction effects and energy barrier distribution on the magnetic relaxation of nanocrystalline hexagonal ferrites

The static and dynamic magnetic properties of nanocrystalline ${\mathrm{BaFe}}_{10.4}$ ${\mathrm{Co}}_{0.8}$ ${\mathrm{Ti}}_{0.8}$ ${\mathrm{O}}_{19}$ M-type doped barium ferrite were studied in detail to clarify the effect of interactions on the magnetic relaxation of an assembly of small particles. The logarithmic approximation was unable to account for the magnetic relaxation of the sample. Interaction effects were analyzed from the low-field susceptibility, ΔM plots and the time dependence of thermoremanence, indicating that demagnetizing interactions led to an enhancement of both the relaxation rate at low temperatures and the amount of the lowest energy barriers. It is thus suggested that care should be taken when analyzing thermoremanent data at low temperature, in order not to confuse these experimental findings with the signature of macroscopic quantum tunneling.