Tunneling in epitaxial Fe/Si/Fe structures with strong antiferromagnetic interlayer coupling

Fe(5 nm)/Si(0.8–2 nm)/Fe(5 nm) structures are grown by molecular-beam epitaxy on Ag(001) buffered GaAs substrates. Ferromagnetic tunneling junctions with crossed electrodes and junction areas ranging from 22 to 225 μm2 are patterned using photolithography. Antiparallel alignment of the magnetizations due to antiferromagnetic interlayer coupling, which is confirmed by longitudinal magneto-optical Kerr effect hysteresis loops, exists for the whole range of spacer thicknesses. Transport properties in current perpendicular to the sample plane geometry are examined by the four-point method in the temperature range from 4 K to room temperature. As a function of spacer thickness, the junctions show a strong increase of the resistance times area product from ≈1 Ω μm2 to more than 10 kΩ μm2. The dI/dV−V curves are parabolic and asymmetric and thus characteristic for trapezoidal tunneling barriers. The mean barrier heights derived from Brinkman fits range from 0.3 to 0.8 eV. The zero-bias resistance of the tunneling junctions moderately decreases with temperature by less than 10% over the whole measured temperature range. All these transport properties fulfill the necessary and sufficient criteria for elastic tunneling.