Temperature dependence of electrical resistivity in (Fe1-xTix)(3)Al alloys

We report on the temperature dependence of electrical resistivity in (Fe1-x Tix)(3)Al alloys with Ti compositions x = 0-0.33. Samples in the compositio n range 0 less than or equal to x less than or equal to 0.15 are found to e xhibit ferromagnetism with the Curie temperature Te decreasing from 770 K f or x = 0 to 145 K for x = 0.15. The electrical resistivity below about 400 K for these Ti-poor samples increases rapidly with increasing x, but a nega tive temperature derivative of resistivity (d rho /dT) dominates above Te u p to 1000 K and above. In contrast, samples in the range 0.20 less than or equal to x less than or equal to 0.33 are in a paramagnetic state, at least down to 2 K, and exhibit a rapid decrease in the low-temperature resistivi ty with increasing Ti composition x. In particular, the Heusler-type Fe2TiA l (x = 0.33) shows a large positive d rho /dT with the residual resistivity of only about 20 mu Omega cm, in sharp contrast to a closely related syste m Fe2VAl reminiscent of a semiconductor-like behaviour with the resistivity reaching 3000 mu Omega cm at 2 K. This can be explained by the fact that F e2TiAl possesses a much higher density of states at the Fermi level than Fe 2VAl, as deduced from the low-temperature specific-heat measurements supple mented by the band calculations in literature. The reason for the possessio n of a large positive d rho /dT in Fe2TiAl is discussed in relation to the Bloch-Gruneisen law.