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

•We investigated transport properties in the double MgO barrier MTJ with Fe nanoparticles.•Superparamagnetic behavior and Coulomb blockade effect attributed to the Fe nanoparticles were observed.•We found an enhancement in the TMR when the size of the Fe nanoparticles decreases.•The enhancement is tentatively attributed to an increase in the spin polarization.

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.