Tunneling magnetoresistance in Fe/MgO granular multilayers.

We have investigated the transport and magnetotransport properties in Fe/MgO multilayers around the Fe percolation threshold as a function of the temperature and the nominal thickness of iron layer (t). Electrical resistivity measurements allowed us to disclose the charge transport mechanisms involved, which are closely related to the degree of discontinuity in the Fe layers. The samples with Fe thickness below percolation threshold (t∼0.8 nm) exhibit isotropic magnetoresistance (MR), which can be understood considering spin-polarized electron tunneling between nanometer-sized, superparamagnetic Fe grains. The MR ratio increases with decreasing temperature from ∼3% at room temperature to ∼10% at 30 K. The temperature dependence of MR can be explained satisfactorily in terms of a modified Mitani’s model. [ABSTRACT FROM AUTHOR]