Low-temperature relaxation process and memory effect in a nonstoichiometric magnetite of Fe3−δO4 with δ=0.03

The low-temperature relaxation process has been investigated in a nonstoichiometric magnetite Fe3−δO4 with δ=0.03. Far below the Verwey transition at TV=90 K, the measurements of AC susceptibility χac display a frequency-dependent anomaly of the shoulder in χ' accompanied with the peak in χ″ and their weak thermal hysteresis. These low-temperature anomalies are related to a thermal relaxation process owing to the domain-wall mobility and extra electron exchange inside the walls. Moreover, the low-temperature relaxation process is revealed to exhibit strong memory effect via field-cooling magnetization measurements. Interesting discrete sudden jumps are observed during the logarithmic decay of magnetization in zero field with aging time, indicating the spontaneous magnetization reversals via adjustment of domain configuration.