Model Calculations for Spin‐Density‐Wave Instabilities in Itinerant Magnets

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Abstract
By evaluation of a generalized Stoner criterion everywhere on the Brillouin zone the instability of the paramagnetic state (PS) vs. a first ordered state (FOS) of spin‐density‐wave type at T = 0 is investigated for a simple but non‐trivial two‐dimensional model of itinerant magnetism. As main results (i) the pitch q0 of the FOS varies continuously with the band‐filling leading to an incommensurate magnetic structure in the most cases, and (ii) the variation of q0 occurs along some symmetry axes of the Brillouin zone. By (ii) a long‐standing conjecture is proved for the model considered. (i) shows that it is not justified to restrict to fixed magnetic structures when setting up theories of itinerant magnetism. First discussions on the meaning of these findings for the results of a more complete description (including the fully developed ordered state and finite temperatures) are given.

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