Abstract
We have studied magnetotransport in organic-inorganic hybrid multilayer junctions. In these devices, the organic semiconductor tris(8-hydroxyquinoline) aluminum formed a spacer layer between ferromagnetic (FM) Co and Fe layers. The thickness of the layer was in the range of 50–150 nm. Positive magnetoresistance (MR) was observed at 4.2 K in a current perpendicular to plane geometry, and this effect persisted up to room temperature. The devices’ microstructure was studied by x-ray reflectometry, Auger electron spectroscopy, and polarized neutron reflectometry (PNR). The films show well-defined layers with modest average chemical roughness (3–5 nm) at the interface between the and the surrounding FM layers. Reflectometry shows that larger MR effects are associated with smaller interface width (both chemical and magnetic) and a magnetically dead layer at the interface. The PNR data also show that the Co layer, which was deposited on top of the , adopts a multidomain magnetic structure at low field and a perfect antiparallel state is not obtained. The origins of the observed MR are discussed and attributed to spin-coherent transport. A lower bound for the spin-diffusion length in was estimated as at 80 K. However, the subtle correlations between microstructure and magnetotransport indicate the importance of interfacial effects in these systems.
4 More- Received 1 October 2008
DOI:https://doi.org/10.1103/PhysRevB.79.075312
©2009 American Physical Society