In situ study of the temperature-dependent magnetoresistance of ultrathin epitaxial Fe films on GaAs(1 0 0)

An in situ magnetoresistance apparatus was used to carry out electrical transport measurements for various temperatures (100-300 K) on ultrathin iron films (1.0-8.0 ML) epitaxially grown on GaAs substrate. At 250 K, we observed a ''GMR-like'' magnetoresistance for a 2.5 ML thick Fe film attributed to the tunneling between the superparamagnetic clusters. Further cooling to 100 K established the onset of ferromagnetic ordering of the clusters giving rise to an anisotropic magnetoresistance signal