Influence of ultra-thin Au interface layers on the structure and magnetic anisotropy of Co films.

摘要

I have investigated the influence of an ultra-thin Au interface layer on the magnetic anisotropy of Co-Pd and Co-Cu structures. Sandwich structures of the form X/Co/Y/Cu/Si(111), with (X, Y) = (Pd, Pd), (Au, Pd), (Pd, Au), (Cu, Cu), (Au, Cu), and (Cu, Au) were studied. For each structure, a Au layer of systematically varied thickness (t{dollar}rmsb{lcub}Au{rcub}){dollar} was inserted at one Co interface. I also investigated Co/Pd and Co/Cu multilayer systems. For each Co-Pd sandwich structures a maximum is observed in the magnetic anisotropy for t{dollar}rmsb{lcub}Au{rcub}{dollar} = 1 to 1.5 atomic monolayer (ML). For the Co/Pd multilayer system, a maximum in coercivity occurs with t{dollar}rmsb{lcub}Au{rcub}{dollar} = 0.5 ML. For each Co-Cu sandwich structure except (X, Y) = (Cu, Au), a minimum in magnetic anisotropy is observed at t{dollar}rmsb{lcub}Au{rcub}{dollar} = 1 ML. For the Co/Cu multilayer system, a decrease in magnetoresistance was seen with increased t{dollar}rmsb{lcub}Au{rcub},{dollar} except in multilayers with a relatively thin Co layer thickness ({dollar}sim{dollar}3 ML) which display a peak in magnetoresistance is seen at t{dollar}rmsb{lcub}Au{rcub}{dollar} = 1 ML. I have also investigated the strain, surface alloying, and surface (interface) roughness of these systems using RHEED, XPS, and LAXD. Analysis of these measurements reveals some correlation between magnetic anisotropy and both strain and surface roughness. Based on my investigations, I conclude that the most likely cause for the non-monotonic changes seen in anisotropy is changes in the surface magnetocrystalline anisotropy. While strain and surface roughness may also play a role, I believe that the influence of the ultra-thin Au interlayer on the orbital hybridization and electronic environment at the interface is dominant.