46 research outputs found
Electronic Structure, Local Moments and Transport in Fe_2VAl
Local spin density approximation calculations are used to elucidate
electronic and magnetic properties of Heusler structure Fe_2VAl. The compound
is found to be a low carrier density semimetal. The Fermi surface has small
hole pockets derived from a triply degenerate Fe derived state at Gamma
compensated by an V derived electron pocket at the X point. The ideal compound
is found to be stable against ferromagnetism. Fe impurities on V sites,
however, behave as local moments. Because of the separation of the hole and
electron pockets the RKKY interaction between such local moments should be
rapidly oscillating on the scale of its decay, leading to the likelihood of
spin-glass behavior for moderate concentrations of Fe on V sites. These
features are discussed in relation to experimental observations of an unusual
insulating state in this compound.Comment: 16 pages, RevTeX, 5 figure
Excitonic Correlations in the Intermetallic Fe2VAl
The intermetallic compound Fe2VAl looks non-metallic in transport and
strongly metallic in thermodynamic and photoemission data. It has in its band
structure a highly differentiated set of valence and conduction bands leading
to a semimetallic system with a very low density of carriers. The pseudogap
itself is due to interaction of Al states with the d orbitals of Fe and V, but
the resulting carriers have little Al character. The effects of generalized
gradient corrections to the local density band structure as well spin-orbit
coupling are shown to be significant, reducing the carrier density by a factor
of three. Doping of this nonmagnetic compound by 0.5 electrons per cell in a
virtual crystal fashion results in a moment of 0.5 bohr magnetons and destroys
the pseudogap. We assess the tendencies toward formation of an excitonic
condensate and toward an excitonic Wigner crystal, and find both to be
unlikely. We propose a model is which the observed properties result from
excitonic correlations arising from two interpenetrating lattices of
distinctive electrons (e_g on V) and holes (t_2g on Fe) of low density (one
carrier of each sign per 350 formula units).Comment: 8 2-column pages, 8 postscript figure