Cr magnetization reversal at the CrO₂/RuO₂ interface: Origin of the reduced GMR effect

Due to very high spin polarization in CrO₂ and its good epitaxy, in principle, CrO₂/RuO₂/CrO₂ trilayers should show significant giant magnetoresitive (GMR) effects, but very small GMR has experimentally been observed so far. Here, we report our soft x-ray resonant reflectivity results at the Cr L_2,3 edges performed on (100) CrO ₂/RuO₂ bilayer. By the use of linear and circular polarized light, this method is able to determine the chemical and the magnetic profiles including roughness or diffusion length. We could clearly exclude the presence of an induced Ru magnetization at the CrO₂/RuO₂ interface as an origin for the reduced GMR effect. On the other hand, we found instability to an antiparallel-oriented CrO₂ magnetization top layer at the RuO₂ interface. No tendency of a dead layer could be found. This result directly explains the rather small GMR observed in this system.