Perpendicular magnetic anisotropy and perpendicular exchange bias in sputter-deposited CoO/CoPt multilayer

Abstract

The structural and magnetic properties of room-temperature sputter-deposited CoO/CoPt multilayer have been investigated. It was found that the multilayers show strong perpendicular magnetic anisotropy (PMA) at room temperature. Moreover, after perpendicular field cooling below the Néel temperature of CoO layer, the multilayer with antiferromagnet (AF)/ferromagnet (FM) interfaces exhibits perpendicular exchange bias (PEB). And also the PMA of the multilayer is enhanced after field cooling process. This is considered due to the strong interfacial exchange coupling between the CoPt and CoO layers, which is further confirmed from the significantly enhanced perpendicular coercivity. Similar with the reported Co/noble-metal structures, the strong PMA found here also shows clear interface effect. However, with the multilayer structure studied here, the PMA can survive with relative thicker ferromagnetic layer (tFM ∼ 2.3 nm) at as-deposited state. Therefore, the PMA found in AF/FM multilayer could be partially attributed to the interfacial AF-FM exchange coupling. On the other hand, structural characterization results indicate a well-defined layer structure and strong (111) texture for CoPt layers. CoO layer here provides a good seed layer for the growth of textured CoPt layer. As [111] is one of the easy axis for the fcc CoPt, the (111) texture should also benefit the PMA. Such PMA and PEB originating from the interface would give new parameters to control the magnetic properties especially for multilayer systems.