Effect of off-stoichiometry on the transport properties of the Heusler-typeFe2VAlcompound

Abstract

We report on the effect of off-stoichiometry on the temperature dependence of electrical resistivity, the Seebeck coefficient, and the Hall coefficient in the Heusler-type Fe 2 VAl compound. While the stoichiometric Fe 2 VAl exhibits a semiconductorlike resistivity behavior, a small deviation of the Al content from stoichiometry causes a significant decrease in the low-temperature resistivity and a large enhancement in the Seebeck coefficient. Substantial enhancements for the Seebeck coefficient are in reasonable accord with changes in the Hall coefficient and can be explained on the basis of the electronic structure, where the Fermi level shifts slightly from the center of a pseudogap due to off stoichiometry.

Weak itinerant ferromagnetism in Heusler-typeFe2VAl0.95

“…7͒ and seems to be consistent with the value of the Hall coefficient of Fe 2 VAl 0.95 . 7,12 The observed value ␥ Ϸ 12 mJ mol −1 K −2 at H = 0 is rather large when we consider the carrier concentration, n Ϸ 0.06, and the value of normal metals, ␥ Ϸ 1 mJ mol −1 K −2 . Consequently, the enhancement factor m ‫ء‬ / m e is ϳ30, where m e is the bare electron mass.…”

“…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.…”

“…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.…”

“…Another interesting aspect of Fe 2 VAl is its potential for application in thermoelectric devices, since off-stoichiometry and heattreatment procedures may results in an enhancement of the Seebeck coefficient. 6,11,12 In Fe 2+x V 1−x Al ͑Refs. 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.…”

“…7,9,10 Al poor Fe 2 VAl 1−␦ ͑␦ Ͼ 0͒, seems to undergo a ferromagnetic transition and shows metallic conduction below room temperature. 12 The Fe 2 VAl 1−␦ system at ␦ Ͼ 0 yields the opportunity to examine quantitatively not only the magnetic but also the transport and thermal properties within the framework of itinerant electron ferromagnetism, as established for intermetallic compounds, such MnSi and ZrZn 2 . 19 In this paper we report a comprehensive study of the low temperature bulk properties of Fe 2 VAl 0.95 , notably magnetization, electrical resistivity, and specific-heat measurements.…”