Interface-driven manipulation of the magnetic anisotropy of ultrathin Co films on Pt(111): Substrate deposition of hydrogen and model calculations

Abstract

The magnetic anisotropy energy (MAE) and the resulting spin-reorientation transitions of Co/Pt(111) ultrathin films are investigated by manipulating the Co/Pt interface with controlled adsorption of hydrogen prior to Co deposition. In situ low-energy electron-diffraction and surface magneto-optical Kerr-effect measurements are performed on Co films grown at low temperatures. The results show that interface H deposition leads to a remarkable change in the magnetization direction from perpendicular to in-plane, even for the thinnest Co films, which is accompanied by an important increase in the coercive force. Layer-resolved self-consistent electronic calculations of the MAE are performed in order to identify the interface contributions responsible for perpendicular magnetic anisotropy (PMA) and to quantify how the MAE depends on various possible adsorbate-induced modifications in the local magnetic moments. The results show that the PMA is quite insensitive to changes in the local magnetic moments at the Co film surface even if they are relatively large. However, the PMA depends crucially on the Co-interface moments, on the Pt-interface moments induced by the proximity to Co, and on the resulting spin-orbit interactions at the Pt atoms. The observed suppression of PMA by interface H adsorption is interpreted as the consequence of the reduction in the interface-Pt moments which, originates either a reduction in the Co-interface moments or at a decoupling of the Pt substrate from the magnetic film. Experiment and theory thus prove the dominant role of the Co-Pt interface MAE on the development of the relative stability of perpendicular and in-plane magnetization directions. The magnetic properties of ultrathin films may thus be tailored to a large extent by adsorbates trapped at $3d\text{\ensuremath{-}}4d$ or $3d\text{\ensuremath{-}}5d$ film-substrate interfaces.