Effect of static and dynamic disorder on electronic transport in RCo₂ compounds: Ho(Al_xCo_1−x)₂ alloys

We present experimental results on thermoelectric power (S) and electrical resistivity (ρ) of pseudobinary alloys Ho(Al_xCo_1−x)₂ (0≤x≤0.1), in the temperature range 4.2 to 300 K. The work focuses on the effects of static (induced by alloying) and dynamic (induced by temperature) disorder on the magnetic state and electronic transport in a metallic system with itinerant metamagnetic instability. Spatial fluctuations of the local magnetic susceptibility in the alloys lead to the development of a partially-ordered magnetic ground state of the itinerant 3d electron system. This results in a strong increase of the residual resistivity and a suppression of the temperature-dependent resistivity. Thermopower exhibits a complex temperature variation in both the magnetically ordered and in the paramagnetic state. This complex temperature variation is attributed to the electronic density-of-states features in vicinity of Fermi energy and to the interplay of magnetic and impurity scattering. Our results indicate that the magnetic enhancement of the Co 3d band in RCo₂-based alloys upon a substitution of Co by nonmagnetic elements is mainly related to a progressive localization of the Co 3d electrons caused by disorder. We show that the magnitude of the resistivity jump at the Curie temperature for RCo₂ compounds exhibiting a first-order phase transition is a nonmonotonic function of the Curie temperature due to a saturation of the 3d-band spin-fluctuation magnitude at high temperatures.