Inverse magnetoresistance in Co/Ru/Co and doped Co/Ru/Co0.92Ru0.08 sandwiches

The investigation of the transport properties of Co(3.2 nm)/Ru(t(Ru))/Co(3. 2 nm) and the doped Co(3.2 nm)/Ru(t(Ru))/Co92Ru8(3.2 nm) sandwiches series is reported, where t(Ru) is the thickness of the Ru layer. Inverse magnetor esistance (MR) for all spacer layer thicknesses in the doped series and for sandwiches which present no antiferromagnetic coupling in the nondoped ser ies is observed. This behavior is the consequence of the competition betwee n bulk and interface spin-dependent scattering which contribute to negative and positive (inverse) MR, respectively. Detailed analysis of the results indicates that the main effect of the doping is to reduce the bulk spin-dep endent scattering whose contribution becomes smaller than the interface spi n-dependent scattering one. This gives rise to an inverse MR. This is furth er supported by ab initio calculations of the density of states at the Ferm i level for pure Co and CoRu alloys as well as experimental temperature dep endent magnetization and MR measurements performed for the two series at ro om and low temperature. [S0163-1829(99)04613-5].