Magnetotransport properties of ferromagnetic LaMnO3+δ nano-sized crystals

Transport and magnetic properties of LaMnO3+δ nanoparticles with average size of 18 nm have been investigated. The ensemble of nanoparticles exhibits a paramagnetic to ferromagnetic (FM) transition at TC∼246 K, while the spontaneous magnetization disappears at T≈270 K. It was found that the blocking temperature lies slightly below TC. The temperature dependence of the resistivity shows a metal–insulator transition at T≈192 K and low-temperature upturn at T<50 K. The transport at low temperatures is controlled by the charging energy and spin-dependent tunnelling through grain boundaries. The low temperature I–V characteristics are well described by indirect tunnelling model while at higher temperatures both direct and resonant tunnelling dominates.