Ultrasmooth magnetic layers for advanced devices (ULTRASMOOTH)

Basic data for this project

Description

The main goal of the european network “Ultrasmooth” (www.ultrasmooth.org) is the generation of smoother magnetic layers both by testing various growth techniques such as sputtering and molecular beam epitaxy (MBE), and by post-processing techniques such as ion irradiation. Our specific objectives are the control and optimisation of magnetic domain wall propagation versus nucleation in Pt/Co/Pt ultrathin films with perpendicular magnetic anisotropy (PMA). The PMA systems are of major interest for ultra-high density magnetic recording. Indeed, for Pt/Co/Pt structures with small Co thickness (< 1 nm), interface effects can be strong enough to overcome the magnetocrystalline and macroscopic shape anisotropy and to induce a perpendicular easy axis of magnetization. We have studied the influence of substrate roughness on both sputtered and MBE grown Pt/Co/Pt ultrathin films. We used either standard MgO substrates or oxygen plasma treated ones. It was shown that a low-energy (20-100 eV) oxygen plasma removes durably the carbon contamination from the MgO surface, leading to a reduced roughness. We measured with AFM a rms roughness of 0.65 Å for the standard MgO, which was reduced to 0.25 Å for the smoothed substrate (oxygen plasma, 60 eV). A first sample series (Univ. Kaiserslautern) showed distinct magnetic properties for MBE grown layers as a function of Co thickness depending on the susbtrate roughness. Preliminary results for the MBE grown samples in Orsay for a Co thickness of 8 Å showed PMA only in the case of the smoothed substrate. Using PMOKE, we compared this result with sputtered films (Univ. Leeds), where the substrate roughness showed only a small effect on the hysteresis cycle. We will also discuss magneto-optical microscopy imaging results of the magnetization reversal process on both sputtered and MBE grown films.