Vicinal substrates provide unique opportunities to engineer the magnetic anisotropies of magnetic ultrathin films. Here we study Co layers on step-bunched Si(111) substrates, with or without a Cu interlayer, taken as model samples. To correlate their interface morphology with the step-induced magnetocrystalline anisotropy and the second-order optical polarization, the magnetization reversal, ferromagnetic resonance, and the interface-induced nonlinear magneto-optical spectroscopic response was

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... nvestigated. We show that both the magnetic anisotropy of the Co layer and the nonlinear magneto-optical response are strongly modified by the addition of the Cu buffer. Thus, the Cu layer reduces the influence of step bunches on the in-plane anisotropy while simultaneously changing the uniaxial anisotropy constant. This is accompanied by a relative change in the rotational harmonics of the nonlinear optical signals that reflect the changes in the interface structure.