Abstract
The influence of the contact between monodisperse Fe3O4 nanoparticles (NPs) on the spin-dependent transport mechanism has been investigated by only changing the cold-press pressures from 20.0 MPa to 5.0 GPa. For the sample cold-pressed under 20.0 MPa, the temperature dependence of resistivity ρ-T curve is best fitted by the log ρ ∝ T−1/2 relation, suggesting the Efros's variable range hopping (VRH) mechanism, while the ρ-T curves of the samples cold-pressed under 1.0 GPa to 5.0 GPa can be best fit with the relation of log ρ ∝ T−1/4, revealing the Mott's VRH mechanism. The different mechanisms are related to the interspacing dependence of charging energy and exchange energy between NPs. Monte Carlo simulations indicated that the charging energy plays a dominant role in the former mechanism, while the spin-dependent exchange energy is dominated in the latter one.
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