Magnetotransport in Fe3 O4 nanoparticle arrays dominated by noncollinear surface spins

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 noncollinear surface spins. All MRs as a function of field can be fitted accurately by a Langevin-like function.