Effect of surface roughness on magnetic properties of Co films on plasma-etched Si(100) substrates

Abstract

Magnetic and morphological properties of ∼970-Å-thick Co films, deposited simultaneously on ten plasma-etched Si(100) substrates, were measured through the magneto-optic Kerr effect (MOKE) technique, ferromagnetic resonance (FMR), magnetic force microscopy (MFM), and atomic force microscopy. As the etch time t increased from 0 to 100 min, the vertical interface width w of Co films increased from ∼5 to ∼1400 Å; the lateral correlation length ξ, from ∼300 to ∼10 500 Å. The MOKE and FMR measurements gave the in-plane azimuthal angular dependence of the hysteresis loops and the ferromagnetic resonance absorption spectra, respectively. From MOKE and FMR, the smoother films showed uniaxial magnetic anisotropy (t⩽40 min). The uniaxial anisotropy decreased with the increase of the surface roughness and disappeared for the roughest films (t=60 and 100 min). The MOKE hysteresis loop measurements suggested that, with the increasing surface roughness, the magnetization reversal changed gradually from magnetization rotation dominated for the smoothest films to domain-wall motion dominated for the roughest films. The MFM images of the films showed anisotropic magnetic domain contrasts for the smooth film, and the subsequent fragmentation of these domains as the roughness parameters increased. This supports the results of the MOKE and FMR measurements.