We have investigated from first-principles an electronic structure and magnetism in MnB4 compound with experimentally observed orthorhombic C12/m1 structure. It is found that Mn tetra-borides (MnB4) is found to have metallic ground state with well defined local Mn magnetic moments. This conclusion was drawn from calculation within full potential Linear Augmented Plane Wave method and Korringa-Kohn-Rostocker method using Disordered Local Moment Approximation. We have shown using Lichtenstein Green function method that magnetic exchange interactions between Mn moments are strongly ferromagnetic along 1D-chains of Mn atoms and they are practically vanishing between the chains. The metallic state appears to exhibit a strongly one-dimensional character since the single metallic band show dispersion only in one reciprocal lattice dimension. Thus it appears that MnB4 may be a perfect one-dimensional one-band Hubbard model system. Although LSDA predicts the magnetism in this system it may well be superconductor at low temperatures due to the correlation effects beyond mean field like approach.
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