Effects of the Annealing Temperature before Cooling under Magnetic Field on Perpendicular Exchange Coupling in (Pt/Co)5/NiO

摘要

The effects of the annealing temperature before cooling under a magnetic field onthe perpendicular exchange coupling in Pt/Co multilayers directly coupled to aNiO layer are studied in the NiO layer thickness range of 1–4 nm. The obtainedresults reveal that the exchange bias (EB) field and the magnetization reversalprocess depend on the NiO layer thickness as well as on the annealing temperature.Positive EB fields are observed, especially for 4 nm-thick NiO layer.However, the values obtained here are low where the largest value is 2.6mT. Thisresult is attributed to weak antiferromagnetic (AFM) coupling at the Co/NiOinterface. These results agree with a blocking temperature of about 300 K. Due tothe low blocking temperature, the AFM interfacial spins direction is tilted withrespect to the ferromagnet magnetization easy axis. As a consequence, the NiOAFM layer manifests at the Co/NiO interface a weak magnetization perpendicularcomponent giving rise to a weak interfacial exchange coupling which leads to lowH_(EB) values.