  From the beginning of molecular theory, the interplay of chirality and
magnetism has intrigued scientists. There is still the question if
enantiospecific adsorption of chiral molecules occurs on magnetic surfaces.
Enantiomer discrimination was conjectured to arise from chirality-induced spin
separation within the molecules and exchange interaction with the substrate's
magnetization. Here we show that single helical aromatic hydrocarbons undergo
enantioselective adsorption on ferromagnetic cobalt surfaces. Spin and
chirality sensitive scanning tunneling microscopy reveals that molecules of
opposite handedness prefer adsorption onto cobalt islands with opposite
out-of-plane magnetization. As mobility ceases in the final chemisorbed state,
it is concluded that enantioselection must occur in a physisorbed transient
precursor state. State-of-the-art spin-resolved ab initio simulations support
this scenario by refuting enantio-dependent chemisorption energies. These
findings demonstrate that van der Waals interaction should also include
spin-fluctuations which are crucial for molecular magnetochiral processes.
