Annealing effects on the magnetic and magnetotransport properties of iron oxide nanoparticles self-assemblies.

We report a systematic study of the effects of vacuum annealing in the structural, magnetic and transport properties of self-assembled ∽10 nm Fe 3 O 4 nanoparticles. The high temperature treatment decomposes the organic coating into amorphous carbon, reducing the electrical resistivity of the assemblies by 4 orders of magnitude. At the same time, the annealing reduces the Fe 2+ /Fe 3+ ratio, indicating an important surface oxidation, and increases the number of defects and hot-spots in the gap between the nanoparticles. This is reflected in the reduction of the spin dependent tunneling, which reduces the interparticle magnetoresistance. This work shows the importance of optimizing the nanostructure fabrication for increasing the tunnelling current without degrading the spin polarized current.