Interspacing dependence of spin-dependent variable range hopping for cold-pressed Fe3O4 nanoparticles

Abstract

The influence of the contact between monodisperse Fe3O 4 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 Efross 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 Motts 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. © 2013 AIP Publishing LLC.