Proximity magnetoresistance in Au80Fe20 and Au70Fe30 below the ordering temperature

The magnetization and magnetoresistance of Au80Fe20 and Au70Fe30 melt-spun ribbons have been measured between 2 and 300 K. The solid solution Au80Fe20, paramagnetic at room temperature, exhibits a transition to a frustrated ferromagnetic state on lowering T. The solid solution Au70Fe30 is in a similar ordered state over the entire temperature interval. A negative magnetoresistance is observed in both systems. In Au80Fe20, its functional dependence on magnetization gradually changes from parabolic (typical of the paramagnetic phase) to box-like with lowering T. In Au70Fe30, the shape of the curves is always box-like. In both alloys, this effect exhibits a nonmonotonic behavior with temperature. The magnetoresistance of these alloys arises from the spin-dependent scattering of conduction electrons at the interfaces between adjacent regions of magnetic coherence of size comparable to the electron mean free path. This effect is therefore referred to as the proximity magnetoresistance. Two magnetization mechanisms independently acting in these systems are disentangled by combining magnetic and magnetoresistance measurements. In this way the spin patterns of these magnetic systems, characterized by a magnetic coherence range of the order of few nanometers, can be effectively studied. (C) 2002 American Institute of Physics.