Abstract
Recent experimental results of Fe3O4 in polycrystalline film, powder compact, and single crystal form have indicated that boundaries play an important role in magnetoresistance effect. In this paper, the complex impedance analysis is used to evaluate the contribution of particle boundary to conduction process in Fe3O4 powders. Considering particle boundaries with different thicknesses, we developed a random resistor-capacitor network model to investigate the influence of magnetic field on impedance behaviors. The fitting results to experimental data indicated that two kinds of conduction mechanisms, spin-dependent tunneling and spin-independent hopping, dominate the transport process in particle boundaries. The capacitive transport through particles with a size of 10–20nm may yield negative magnetoreactance. It is also found that magnetic field has little influence not only on the competition between resistive and capacitive path, but also phase angle Φ(f). Finally, it can be deducted that the magnetoreactance effect could be enhanced in this granular sample if the particle size is less than 10–20nm.
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