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

Abstract

The effects of the annealing temperature before cooling under a magnetic field on the perpendicular exchange coupling in Pt/Co multilayers directly coupled to a NiO layer are studied in the NiO layer thickness range of 1–4 nm. The obtained results reveal that the exchange bias (EB) field and the magnetization reversal process 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 2.6 mT. This result is attributed to weak antiferromagnetic (AFM) coupling at the Co/NiO interface. These results agree with a blocking temperature of about 300 K. Due to the low blocking temperature, the AFM interfacial spins direction is tilted with respect to the ferromagnet magnetization easy axis. As a consequence, the NiO AFM layer manifests at the Co/NiO interface a weak magnetization perpendicular component giving rise to a weak interfacial exchange coupling which leads to low values.

Exchange Bias and Vertical Magnetic Shift on Co−CoO Thin Films

“…However, in some cases of FM/AFM coupling a positive shift was also observed. [ 24 ] This can partly explain our results. Gredig et al reported a temperature dependence EB in these samples.…”