Effect of surface roughness on magnetization reversal of Co films on plasma-etched Si(100) substrates

Co films $∼970$ Å thick were deposited, simultaneously, on ten plasma-etched Si(100) substrates with various etch times $t.$ The surface morphologies and magnetic properties of the Co films were measured by atomic force microscopy (AFM) and magneto-optic Kerr effect (MOKE) technique. The analysis of the AFM images shows that as the etch time $t$ increased from 0 to 100 min, the vertical interface width $w$ increased from $∼5$ to $∼1400 Å;$ the lateral correlation length ξ increased from $∼300$ to $∼10 500 Å.$ The MOKE measurements provided the in-plane azimuthal angular dependence of the hysteresis loops and the change of loop shapes with the surface roughness. It was found that the magnetization reversal process changed with the surface roughness. Magnetization rotation dominated the magnetization reversal for the smoothest films. As the films roughened, the domain-wall pinning set in, eventually dominating the magnetization reversal for the roughest films. Additionally, the magnetic uniaxial anisotropy in the Co films disappeared as the roughness parameters increased. It was also found from MOKE that the surface roughness strongly affected the coercivity.