Magnetism in expanded 3d transition metals

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For sufficiently large expansion of the lattice, transition metals will eventually exhibit ferromagnetism in accordance with Hund’s rule. This problem has been reexamined on the basis of calculations of the paramagnetic susceptibility to determine instabilities of the paramagnetic phase. Comparison of predictions using this method for the critical lattice constant for ferromagnetism are in good agreement with previous total energy calculations. However, this study also yields new predictions of antiferromagnetism for a range of lattice constants less than that for onset of ferromagnetism. The susceptibility is formulated in a multiband generalization of the Stoner approach with many-body effects incorporated within the local-density approximation in density functional theory. Slater–Koster band structures are employed which permit lattice constant variation to be realized through a relatively simple scaling scheme. Both many-body effects and the distribution of primarily single-electron states associated with Fermi surface nesting combine to produce the antiferromagnetic instability under expansion. Nesting is probably necessary for incommensurate antiferromagnetism, and its decrease in importance as the lattice constant continues to increase contributes to the incipient ferromagnetic instability.