TEMPERATURE EFFECT ON MAGNETORESISTANCE IN CU RU SANDWICHES/

Evidence is given of a strong dependence of magnetoresistance on tempe rature in Co/Ru sandwiches. This dependence while weak for thin Ru lay ers is much stronger for thicker Ru layers. In fact, three oscillation s in saturation magnetoresistance and saturation field as a function o f the thickness of the Ru layer t(Ru) are observed at 4.2 K while only one oscillation is found at 300 K. In addition, for thin Ru layers, t (Ru)<11 angstrom, the saturation magnetoresistance is found to decreas e between 4.2 and 300 K. In contrast, for Ru thickness in the range 11 angstrom<t(Ru)<14 angstrom, the behavior is reversed, leading to the increase of the magnetoresistance at 300 K. This behavior is attribute d to the spin disorder occurring at the interfaces at room temperature . Finally, for t(Ru)>14 angstrom the magnetoresistance completely vani shes at 300 K while a relatively high value is still observed for larg e Ru thickness, t(Ru)=80 angstrom, at 4.2 K. This indicates that the m ean free path of the conduction electrons in the Ru layer is strongly reduced from about 100 angstrom at 4.2 K to approximately 14 angstrom at room temperature.