Magnetic structure of bct manganese in the bulk and at the (001) surface

The ground state magnetic properties of bulk bet manganese with atomic volume 13.5 Angstrom(3) have been studied using a tight-binding Hubbard model in the unrestricted Hartree-Fock approximation. Considering the ferromagnetic and four different antiferromagnetic structures, we find a new ground state for tetragonal distortion c/a - 1 below 15%, namely a (110) layer-by-layer antiferromagnet. We have also studied the (001) surface of such a bet lattice with a distortion of 14% as it can be grown epitaxially on Fe(001). Starting from different magnetic configurations in the bulk, we find that the antiferromagnetic order within the surface layer is always lower in energy than the ferromagnetic one, and that the mean surface magnetisation therefore vanishes.