Perpendicular exchange bias at room temperature in (Pt/Co) multilayers coupled to NiO antiferromagnetic layer

Abstract

(Pt/Co) multilayers coupled to NiO exhibit a small exchange bias field HEB which is consistent with a NiO blocking temperature TB of about the room temperature. Direct deposition of nickel oxide on cobalt increased coercivity and induced a weak exchange bias field. The reversal process has also been affected. It changes from a reversal clearly governed by wall propagation initiated by only a few domains to a reversal dominated by wall propagation that is initiated by a larger number of domains leading to an important role in the nucleation. The domains are larger in the sample without NiO. The insertion of a platinum layer with thickness range 0–0.6 nm between Co and NiO acts on the coercivity and the exchange field. The optimal values of HC and HEB are observed for tpt = 0.2 nm. We found that the magnetization reversal process changes from a wall propagation-dominated process for tpt ≤0.2 nm to a domain nucleation dominated process for tpt> 0.2 nm.