An anomalous negative temperature dependence of electrical resistivity has been observed in ͑Fe 12x V x ͒ 3 Al alloys with V compositions up to x 0.35. In particular, the Heusler-type Fe 2 VAl compound is found to be on the verge of magnetic ordering and to exhibit a semiconductorlike behavior with the resistivity reaching 3000 mV cm at 2 K, in spite of the possession of a clear Fermi cutoff as revealed in photoemission valence-band spectra. A substantial mass enhancement deduced from specific heat measurements suggests that Fe 2 VAl is a possible candidate for a 3d heavy-fermion system. [S0031-9007(97)03978-1] PACS numbers: 72.15.Eb, 75.50.Bb, 79.60.Bm, 81.40.Rs Intermetallic compounds Fe 3 Si and Fe 3 Al are wellordered ferromagnets with a D0 3 crystal structure. Recently, Nishino et al. [1,2] found an anomalous temperature dependence of electrical resistivity in a series of the pseudobinary alloys in which Fe atoms are partly replaced by other 3d transition elements. These alloys possess common features characterized by (1) a resistance maximum near the Curie point T c in contrast to an angular change observed in ordinary ferromagnets, and (2) a negative resistivity slope at higher temperatures up to 1000 K and above. The substitution of 3d elements to the left of Fe in the periodic table seems to be responsible for the occurrence of the negative temperature dependence of the resistivity [1,2]. In other words, the elements with less than half-filled d states are more effective for the anomaly than those with more than half-filled ones. Since the substitution of Ti, V, Cr, and Mn always causes a sharp reduction in T c and in magnetization, the anomalous resistance behavior could be attributed to a weakening of ferromagnetism compelled by the substituents [1].The most spectacular feature of the resistance anomaly has been found for ͑Fe 12x V x ͒ 3 Al [2], as well as for. Among them, the ͑Fe 12x V x ͒ 3 Al system is of greater interest because a single phase of the D0 3 structure remains stable over a wide V composition range [2,4]. In this Letter, we demonstrate the occurrence of the negative temperature dependence of the electrical resistivity in ͑Fe 12x V x ͒ 3 Al with V compositions up to x 0.35. In particular, the Heuslertype Fe 2 VAl compound ͑x 0.33͒ exhibits a strong anomaly in a manner similar to a semiconductor. It may be worthwhile mentioning here that such a semiconductorlike negative resistivity slope can also be found for heavyfermion compounds [5], all of which are of f-electron systems. Furthermore, as will be discussed later, the present Fe 2 VAl compound is proved to be in a marginally magnetic state. In this regard, Fe 2 VAl shows an apparent similarity to a nonmagnetic narrow-gap semiconductor, FeSi, which has been classified by Fisk et al.[6] as a unique d-electron system among the family of "strongly correlated" or "Kondo" insulators. In addition to the resistivity measurements, the electronic structure of Fe 2 VAl has been investigated by means of high-resolution photoemission spectrosco...

We report electronic, magnetic and transport properties of (Fe1-x Vx )3 Al alloys with x = 0 - 0.38 and analyse the results on the basis of the measured electronic specific-heat coefficient, the Debye temperature and the magnetic stiffness constant. As the V composition increases, the electrical resistivity increases rapidly at low temperatures and the magnetization decreases significantly in parallel with a sharp reduction in the Curie temperature. In particular, the Heusler-type Fe2 VAl compound (x = 0.33) is found to be in a marginally magnetic state and to exhibit a semiconductor-like behaviour with the resistivity reaching 3000 µ cm at 2 K. Low-temperature specific heat studies demonstrate a substantial decrease in carrier concentration with the V substitution, being consistent with recent band calculations, which predict that Fe2 VAl is a nonmagnetic semimetal with a sharp pseudogap at the Fermi level. A large mass enhancement deduced from the electronic specific-heat measurements suggests that Fe2 VAl is a possible candidate for a 3d heavy-fermion system. The unusual electron transport is mainly attributed to the effect of strong spin fluctuations, in addition to the existence of very low carrier concentrations.

We report on the temperature dependence of electrical resistivity, Seebeck coefficient and Hall coefficient of the Fe 2 VAl 1-y Si y alloys with Si compositions y＝0 0.20. While the Heusler type Fe 2 VAl ( y＝0) exhibits a semiconductor like resistivity behavior, a slight substitution of Si for Al causes a sharp 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 the pseudogap due to the substitution of Si. In particular, the Si substitution of y＝0.10 leads to a large power factor of 5.4×10 -3 W/m K 2 at room temperature, which is comparable to that of conventional thermoelectric materials.

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