Inverse interface Cr magnetization at the CrO2/RuO2 interface: The origin for unexpected small GMR effects

Due to the 100% spin polarization in CrO2 and the good epitaxy CrO2/RuO2/CrO2 trilayers have been proposed to provide extraordinary magneto-resistive effects (GMR), but only very small GMR has been observed so far. We will provide soft X-ray resonant reflectivity results at the Cr L2,3 edges performed on a CrO2/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. On one hand, we can 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 unexpected result directly explains the rather small GMR observed in this system.