  Magnetotransport in arrays of monodisperse magnetite nanoparticles has been
studied as a function of annealing temperatures. Charge transport mechanisms
change from thermally assisted interparticle tunneling to hopping between
Fe-sites within the particle as the interparticle spacing is decreased. Despite
this difference, magnetoresistance (MR) as a function of field shows a
ubiquitous behavior dominated by non-collinear surface spins. All MR as a
function of field can be fitted accurately by a Langevin-like function.
