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

Abstract

We investigate the influence of a nanoscale periodic ripple morphology on the structure and magnetocrystalline anisotropy of thin ferromagnetic (FM) Ni${}_{81}$Fe${}_{19}$, 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.