Calculated magnetocrystalline anisotropy of decorated and undecorated steps on fcc Co(0 0 1)

The in-plane magnetocrystalline anisotropy, of an isolated step along the [1 1̄ 0] direction, on the surface of fcc Co(0 0 1), is calculated using a multi-orbital tight-binding approach. A similar calculation is performed on the same system, when the step is `decoratedʹ with an atomic wire of Cu. Two distinct methods are used, both based on calculations of the total energy with the magnetization parallel and perpendicular to the step. One method applies the standard recursion scheme with up to 400 levels of continued fraction, in order to achieve the required accuracy of 0.01 meV/step atom. The other method is novel, and is based on an exact (semi-analytic) total energy computation of an infinite system using a matrix Möbius transformation technique. The two methods give essentially identical results and the easy axis of magnetization for the undecorated case is along the step as observed experimentally. Decoration of the step changes the anisotropy in the same direction as observed by Weber et al. but the shift is insufficient to rotate the easy axis.