TEMPERATURE EFFECT ON MAGNETORESISTANCE IN CU/RU SANDWICHES

Evidence is given of a strong dependence of magnetoresistance on temperature in Co/Ru sandwiches. This dependence while weak for thin Ru layers is much stronger for thicker Ru layers. In fact, three oscillations in saturation magnetoresistance and saturation field as a function of 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 decrease 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 attributed to the spin disorder occurring at the interfaces at room temperature. Finally, for t(Ru)>14 angstrom the magnetoresistance completely vanishes at 300 K while a relatively high value is still observed for large Ru thickness, t(Ru)=80 angstrom, at 4.2 K. This indicates that the mean 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.