Crossover in the surface anisotropy contributions of ferromagnetic films on rippled Si surfaces

We investigate the influence of a nanoscale periodic ripple morphology on the structure and magnetocrystalline anisotropy of thin ferromagnetic (FM) Ni81Fe19, Co, and Fe films. The ripples are created by ion beam erosion of the Si substrate. The periodic ripple structures induce a uniaxial magnetic anisotropy (UMA) in the FM films as confirmed by ferromagnetic resonance and magneto-optical Kerr effect measurements. The thickness dependence of the UMA reveals an abrupt transition. For a thin film regime there is a corrugated alignment of the magnetic moments and above a critical thickness one has dipolar interactions due to the sinusoidal surface modulations. DOI: 10.1103/PhysRevB.87.024424