CRITICAL-BEHAVIOR OF A MODEL BAND FERROMAGNET

Autor(en): NOLTING, W
DERKELLEN, SB
BORSTEL, G
Stichwörter: HUBBARD-MODEL; Materials Science; Materials Science, Multidisciplinary; Physics; Physics, Applied; Physics, Condensed Matter
Erscheinungsdatum: 1991
Herausgeber: AMERICAN PHYSICAL SOC
Journal: PHYSICAL REVIEW B
Volumen: 43
Ausgabe: 1, B
Startseite: 1117
Seitenende: 1129
Zusammenfassung: 
We investigate the critical behavior of a band ferromagnet within the framework of the Hubbard model. With the aid of a self-consistent moment method the possibility of paraferromagnetic phase transitions is inspected with respect to the s-band occupation n (0 less-than-or-equal-to n less-than-or-equal-to 2) and the Coulomb interaction U. For an fcc lattice structure phase transitions appear when the energy band is more than half filled and U exceeds a critical value (U/W greater-than-or-equal-to 1; W the Bloch bandwidth). They are of first order for slightly more than half-filled bands (up to n almost-equal-to 1.3), arising as consequences of the competition between two coexisting ferromagnetic solutions, which cancel mutually at the transition point. For n greater-than-or-equal-to 1.35 the phase transitions are of second order. The critical phenomena get a strictly universal character, becoming completely n and U independent, with critical exponents of Landau type (alpha = alpha' = 0; beta = 0.5; gamma = 1; delta = 3). In band systems with second-order transitions the paramagnetic, static susceptibility exhibits clear Curie-Weiss behavior, with a paramagnetic Curie temperature-THETA being in most cases substantially greater than T(C).
ISSN: 01631829
DOI: 10.1103/PhysRevB.43.1117

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