Magnetic order and exchange interactions in monoatomic 3d transition-metal chains

Based on first-principles calculations we analyze the magnetic order and the exchange interactions in monoatomic 3d transition-metal chains of V, Cr, Mn, Fe, and Co. While freestanding Fe and Co chains remain ferromagnetic in the entire range of interatomic distances, V, Cr, and Mn chains change their magnetic state from antiferromagnetic (AFM) to ferromagnetic (FM) upon stretching. The corresponding distance-dependent exchange interaction is in striking resemblance to the Bethe-Slater curve. We demonstrate that in combination with the symmetry reduction on the (110) surfaces of Cu, Pd, Ag, and NiAl even a weak chain-surface hybridization is sufficient to dramatically change the magnetic coupling in the chains. In particular, we find a tendency towards antiferromagnetic coupling. The obtained magnetic state of a specific chain depends sensitively on the chemical composition and the lattice constant of the surface. Surprisingly, Cr and Mn chains show a transition from ferromagnetic coupling in freestanding chains to antiferromagnetic coupling on the (110) surfaces of Pd, Ag, and NiAl. For Fe and Co chains on NiAl(110) the FM and AFM states differ by only 2 meV, suggesting the possibility of a more complex, noncollinear magnetic ground state.