  Covalent substrates can give rise to a variety of magnetic interaction
mechanisms among adsorbed transition metal atoms building atomic
nanostructures. We show this by calculating the ground state magnetic
configuration of monoatomic 3d chains deposited on a monolayer of Cu$_2$N grown
on Cu(001) as a function of $d$ filling and of adsorption sites of the one
dimensional nanostructures.
