  A first-principles investigation of the anomalous ferromagnetism of a
quasi-one-dimensional Co chain at the Pt(111) step edge is reported. Our
calculations show that the symmetry breaking at the step leads to an easy
magnetization axis at an odd angle of $\sim20^{\circ}$ {\em towards} the Pt
step, in agreement with experiment [P. Gambardella {\em et al.}, {\em Nature}
{\bf 416}, 301 (2002)]. Also, the Co spin and orbital moments become
noncollinear, even in the case of a collinear ferromagnetic spin arrangement. A
significant enhancement of the Co orbital magnetic moment is achieved when
modest electron correlations are treated within LSDA+$U$ calculations.
