Weak ferromagnetism in Mn nanochains on the CuN surface

We investigate the electronic and magnetic structures of Mn chains supported on a CuN surface, using first-principles LSDA and LDA+U methods. The isotropic exchange integrals and anisotropic Dzyaloshinskii-Moriya interactions between Mn atoms are calculated using the Green's function technique and total energies difference method. It is shown that lattice relaxation and on-site Coulomb interaction are important for an accurate description of the magnetic properties of the investigated nanosystems. Based on a classical spin Hamiltonian we conclude that the Mn antiferromagnetic nanochains on the CuN surface demonstrate weak ferromagnetism. The net magnetic moment and direction of the spin canting are estimated in the framework of a classical spin Hamiltonian. We show that some aspects of the experimental spectrum can be explained using a quantum spin Hamiltonian, with parameters defined from first-principles calculations and extracted from recent STM experiments.