Spin-dependent tunneling in magnetic tunnel junctions with Fe nanoparticles embedded in an MgO matrix

We investigated the transport properties in magnetic tunnel junctions with Fe nanoparticles (nominal thickness: tFe=0.17–1.37 nm) and double MgO barriers. A disappearance of the hysteresis of the Fe nanoparticle magnetization due to its room-temperature superparamagnetic behavior and a large increase in the electrical resistance due to the Coulomb blockade effect were observed for tFe≤0.97 nm. We found an increase in the tunnel magnetoresistance when the tFe decreases, which can be understood as enhancement of the spin polarization for the Fe particles that are smaller in size. Dip and shoulder structures that appeared in the first differential conductance spectra are also discussed.