Tailoring perpendicular magnetic anisotropy in ultrathin Co/Pt multilayers coupled to NiO

Abstract

The nanomagnetism of ultrathin Co/Pt multilayer films is set largely by the microstructure and composition of the interface. To examine these finite-size effects on the Co/Pt magnetism, we have made different Co thickness multilayer films using an ion-beam deposition method with controlled ion energies via an End-Hall voltage VEH, and deposited a layer of NiO to examine the nature of the magnetic anisotropy by way of studying the in-plane and perpendicular magnetism. Examining different Co/Pt multilayers made using different VEH ion energies, we have ascertained that 1.2 nm of Co is the minimum thickness required to establish perpendicular magnetic anisotropy PMA and that no intermixing of Co and Pt at their interface is necessary for PMA to occur. First-principles calculations, consistent with the analysis of electron-energy-loss spectrometry with near atomic resolution, indicate that PMA is due to hybridization of Co and Pt at the interface which results in a perpendicular magnetization axis being set in the Co layer due to a significant lowering of the interfacial anisotropy energy. These results point toward an interesting way to tune PMA in ultrathin Co/Pt multilayers.