Interplay between disorder and quantum and thermal fluctuations in ferromagnetic alloys: the case of UCu2Si2-xGex.

We consider, theoretically and experimentally, the effects of structural disorder, quantum fluctuations, and thermal fluctuations in the magnetic and transport properties of certain ferromagnetic alloys. We study the particular case of UCu2Si2-xGex. The low temperature resistivity, rho(T,x), exhibits Fermi liquid behavior as a function of temperature T for all values of x, which can be interpreted as a result of the magnetic scattering of the conduction electrons from the localized U spins. The residual resistivity, rho(0,x), follows the behavior of a disordered binary alloy. The observed nonmonotonic dependence of the Curie temperature, T(c)(x), with x can be explained within a model of localized spins interacting with an electronic bath. Our results clearly show that the Curie temperature of certain alloys can be enhanced due to the interplay between quantum and thermal fluctuations with disorder.