Magnetoresistance in single Fe(001) ultrathin films

Magnetoresistance in Au(001)-sandwiched Fe(001) ultrathin films was investigated at T = 1.6 K. Effects of both the Fe layer and the Au cap layer were investigated using wedge-shaped Fe and Au cap layers. The total thicknesses of the films were kept much thinner than the mean free path of the conduction electrons in order to enhance the magnetoresistance by electron channeling between the surface and the substrate. The Fe wedge-shaped films in the range d(Fe) = 0-4 Angstrom showed a granular-type giant magnetoresistance (GMR) because of a discontinuity in the Fe layer. The films with d(Fe) = 4-25 Angstrom also showed that the GMR component through the Fe layer is continuous. In the Au cap wedge-shaped films, the GMR component nearly vanished at d(Au) (cap) = 0. The MR ratio increased linearly with d(Au cap) in the range d(Au cap) = 0-50 Angstrom and saturated at d(Au cap) similar to 130 Angstrom. Moreover, the CuO overlayer on the Au cap wedge-shaped film resulted in a 25% decrease in the MR ratio in the whole dAu cap range. These phenomena can be interpreted as differences in spin flip probability for electron reflections on the surface and at the interfaces. (C) 1998 American Institute of Physics. [S0021-8979(98)50311-2].