Magnetic, electrical transport, and hydrostatic pressure studies of the Heusler alloy (iron(1-x)V(x))(3)aluminum

The system (Fe1-xVx)3Al was studied by means of measurements of magnetization, electrical resistivity, and Hall effect as a function of composition, temperature, magnetic field, and hydrostatic pressure. We conclude that the system is magnetically inactive at the composition x = 1/3 in (Fe1-xVx)3Al. For values of x < 1/3, the system is found to be composed of clusters of 9 magnetic Fe atoms coupled together ferromagnetically. The magnetic coupling is of an indirect nature due to the large distances between the Fe atoms. The application of pressure was found to change the Curie-Weiss temperature in a manner consistent with an RKKY type interaction. The magnetic coupling was found to be weak as compared to other indirectly coupled, isolated moment systems; such as, Mn atoms dissolved in Cu and transition metal Zintl compounds. The change in the Curie-Weiss temperature was also analyzed by applying the itinerant electron model of ferromagnetism. Within this model the system was found to exhibit behavior consistent with an inhomogeneous system. The magnitude of the resistivity also changed with the application of pressure. Since the Hall coefficient was found to remain constant with the application of pressure, it is concluded that the change in the resistivity is due to a change in scattering or a change in the effective mass of the carriers. The temperature dependence of the resistivity can be understood qualitatively by the reduction of carriers as evident from measurements of the Hall effect as a function of temperature on the same samples. An upturn is observed in the resistivity as a function of temperature at the lowest temperatures measured. This upturn is consistent with Kondo type behavior and is attributed to the existence of magnetic impurities or site disorder. The observed colossal magnetoresistance (CMR) is in part due to the reduction in spin-disorder scattering brought about by the ordering of the magnetic moments in the sample at temperatures near the Curie temperature. The values of C0, the coefficient of (M/M 0)2 from the magnetoresistance as a function of magnetization, are consistent with weak coupling. The coupling strength is further reduced as the composition approaches the non-magnetic value x = 1/3.