Spin-dependent tunnelling in magnetite nanoparticles

•Spin-dependent tunnelling in 13 nm magnetite nanoparticles made by coprecipitation.•Nanoparticle electrostatic charging effect dominates the carrier transport.•Spin-disorder in the nanoparticle shell region.•High field magnetization 81% of the bulk value.•Evidence of the Verwey transition in the magnetic data. Fe3O4 nanoparticles have been made by a co-precipitation method with an average size of 13 nm. Raman measurements show that there is also a small fraction of maghemite that is not seen in the XRD data. The saturation magnetization is high for this preparation method and the coercive field is low at 300 K. The high field magnetic moment cannot be fitted to a Bloch temperature dependence over the full temperature range, which is likely due to the effect of the Verwey transition at 120 K. Pressed powders shows a magnetoresistance of up to −6.5% at 8 T and 300 K. The magnetoresistance can be fitted to a model where there is a spin-dependent tunnelling between nanoparticles with a spin-disordered shell. The temperature dependence of the resistivity can be attributed to nanoparticle electrostatic charging effects.