Inverse magnetoresistance in Co/Ru/Co and doped ${\mathrm{C}\mathrm{o}/\mathrm{R}\mathrm{u}/\mathrm{C}\mathrm{o}}_{0.92}{\mathrm{Ru}}_{0.08}$ sandwiches

The investigation of the transport properties of $\mathrm{C}\mathrm{o}\left(3.2\mathrm{}\mathrm{}\mathrm{n}\mathrm{m}\right)/\mathrm{R}\mathrm{u}{(t}_{\mathrm{Ru}})/\mathrm{C}\mathrm{o}(3.2\mathrm{}\mathrm{}\mathrm{n}\mathrm{m})$ and the doped $\mathrm{C}\mathrm{o}\left(3.2\mathrm{}\mathrm{}\mathrm{n}\mathrm{m}\right)/\mathrm{R}\mathrm{u}{(t}_{\mathrm{Ru}})/{\mathrm{Co}}_{92}{\mathrm{Ru}}_8(3.2\mathrm{}\mathrm{}\mathrm{n}\mathrm{m})$ sandwiches series is reported, where $t_{\mathrm{Ru}}$ is the thickness of the Ru layer. Inverse magnetoresistance (MR) for all spacer layer thicknesses in the doped series and for sandwiches which present no antiferromagnetic coupling in the nondoped series is observed. This behavior is the consequence of the competition between 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-dependent scattering whose contribution becomes smaller than the interface spin-dependent scattering one. This gives rise to an inverse MR. This is further supported by ab initio calculations of the density of states at the Fermi level for pure Co and CoRu alloys as well as experimental temperature-dependent magnetization and MR measurements performed for the two series at room and low temperature.