Pseudogap and transport properties inFe3−xVxAl

Abstract

We have measured the Hall resistivity for the intermetallic compound Fe 3Ϫx V x Al y ͑xϭ0.5-1.05; y ϭ0.95,1.05͒ at room temperature. The Hall coefficient changed its sign from positive to negative around the Heusler composition ͑i.e., xϭyϭ1͒ with increasing x value or decreasing y value. We have measured the temperature dependence of the Hall coefficient and the electrical resistivity for Fe 1.98 V 1.02 Al and quenched Fe 1.95 V 1.05 Al in the temperature range of 5-300 K. These two compounds showed very different behavior in the electrical resistivity but the behavior of the Hall coefficient was quite similar. At higher temperatures, the Hall coefficient showed a strong temperature dependence but it approached a constant value at low temperatures suggesting that these compounds are semimetals with a pseudogap. The charge carrier density was found to be less than a few tenths per unit cell. The rise of electrical resistivity at low temperatures is not owing to an energy gap but due to magnetic scattering while the negative temperature coefficient at high temperatures is attributable to pseudogap.

Weak itinerant ferromagnetism in Heusler-typeFe2VAl0.95

“…11 and 12͒ and Fe 2 VAl 1−␦ , 12 the thermoelectric power is enhanced for x Ϸ 0 and ␦ Ϸ 0: with a negative sign for x Ͻ 0 and ␦ Ͼ 0, and positive sign for x Ͼ 0 and ␦ Ͻ 0. In the case of stoichiometric Fe 2 VAl the negative temperature coefficient in the electrical resistivity observed up to 1300 K and the constant value of the Hall coefficient at low temperatures 6,7,12 suggest it is a low carrier-density semimetal with a pseudogap at the Fermi level. 6 Antisite defects and magnetic nanoclusters induced by heat treatment and nominal off-stoichiometry bring about ferromagnetism 7,10,13,18 and superparamagnetism.…”

“…In the case of stoichiometric Fe 2 VAl the negative temperature coefficient in the electrical resistivity observed up to 1300 K and the constant value of the Hall coefficient at low temperatures 6,7,12 suggest it is a low carrier-density semimetal with a pseudogap at the Fermi level. 6 Antisite defects and magnetic nanoclusters induced by heat treatment and nominal off-stoichiometry bring about ferromagnetism 7,10,13,18 and superparamagnetism. 18 With increasing x in Fe 2+x V 1−x Al, the excess of Fe atoms occupy the nominal V site and, consequently, Fe 3 Al ͑Fe 2 FeAl͒ clusters are formed ͓notice bulk Fe 3 Al is ferromagnetic with T C = 803 K ͑Refs.…”

“…The presence of antisite Fe atoms on the nominal V site in the FeV 2 Al system brings about a simultaneous enhancement of the magnetization and resistivity at low temperatures. 7,9,10 This led to the claim that localized magnetic moments must be a crucial factor in the strong magnetic scattering of the conduction electrons responsible for the steep rise of the resistivity, the negative temperature coefficient of the resistivity, d / dT Ͻ 0 and a giant magnetoresistance at x Ͼ 0. Thus it is proposed that the steep rise of the electrical resistivity at lower temperature is not due to the energy gap but due to strong magnetic scattering.…”

“…6 Stoichiometric Fe 2 VAl is nonmagnetic and related alloys, such as Fe 2+x V 1−x Al and Fe 2 VAl 1−␦ , exhibit ferromagnetic transitions. 7,[10][11][12][13][14] Consequently, the samples at x Ϸ 0 and ␦ Ϸ 0 are located at the brink of ferromagnetic order, close to the ferromagnetic quantum critical point, i.e., T C → 0. 6,8 Stimulated by these findings, theoretical work claimed Fe 2 VAl is a nonmagnetic semimetal with the pseudogap at the Fermi level.…”

“…Fe 2 VAl and related alloys have attracted considerable attention [6][7][8][9][10][11] since it was claimed that these 3d-electron systems with small carrier concentration, n Ϸ 0.01 per unit formula, 7 exhibit a significant carrier mass enhancement and non-Fermi-liquid behavior. 6 Stoichiometric Fe 2 VAl is nonmagnetic and related alloys, such as Fe 2+x V 1−x Al and Fe 2 VAl 1−␦ , exhibit ferromagnetic transitions.…”