Nanostructuue, interfaces, and magnetic properties in giant magnetoresistive NiO-Co-Cu-based spin valves

Giant magnetoresistive NiO-Co-Cu-based top and symmetric spin valves were studied with emphasis on the role of oxygen partial pressure, p(O-2), in affecting the magnetic pinning of Co by NiO. Results show a correlation between the underlying nanostructure and pinning strength as a function of p(O-2). High-resolution transmission electron microscopy show that at progressively higher oxygen partial pressures, NiO-Co interface becomes crystallographically disordered, in part, due to the oxidation of Co layer on which NiO is deposited; an amorphous film is formed at the interface. An optimum p(O-2) interval for the deposition of NiO is identified (similar to 1 X 10(-5)-3.0 X 10(-5) Torr), in which a sharp and crystallographically well-defined NiO-Co interface can exist. Finally, a simple model suggest that defect structures at the NiO-Co interface may play an important role in the magnetization reversal of a NiO-pinned Co layer in an applied field. (C) 1997 American Institute of Physics.