T. Herrmann et W. Nolting, INFLUENCE OF QUASI-PARTICLE DAMPING ON MAGNETIC STABILITY, Physical review. B, Condensed matter, 53(16), 1996, pp. 10579-10588
We propose a modified alloy analogy for the single-band Hubbard model,
by which we investigate the possibility of spontaneous ferromagnetism
in narrow energy bands. It is shown that a proper definition of the f
ictitious alloy enables self-consistent magnetic solutions to be found
. The existence of spontaneous magnetism is mainly influenced by the l
attice structure, the effective Coulomb coupling, and the band occupat
ion. In accordance with the simple Stoner criterion, ferromagnetism ap
pears in strongly correlated electron systems for band occupations, wh
ich locate the chemical potential mu in regions of high quasiparticle
density of states. Rather realistic Curie temperatures are found. The
macroscopic magnetic properties explain themselves via temperature-dep
endent quasiparticle densities of states, quasiparticle band structure
s, and respective spectral densities. It is shown how quasiparticle da
mping may depress quite substantially the stability of magnetic states
by broadening corresponding spectral density peaks. Correlation effec
ts lead to the expected splitting into two quasiparticle subbands (''H
ubbard bands''), and under certain conditions to an additional exchang
e splitting of each of these quasiparticle subbands, as well as to a s
pin-dependent band narrowing, the combination of which gives rise to a
n unconventional ''inverse'' exchange shift at certain positions of th
e Brillouin zone.