Variación térmica de la resistividad eléctrica en nuevos materiales metálicos: compuestos de tierras raras y aleaciones amorfas

The present report describes the method for measuring the temperature dependence of the resistivity between 10 and 300 K that we have developed in our laboratories at the University of Cantabria. This is a four-probe method using ac current and synchronous detection. Also it is analyzed, using the finite element method, the effects of the sample geometry and contacts position in the relationship between the real resistivity and resistivity observed experimentally, even in the case of � [+]anisotropic samples. Subsequently we apply this technique to the study of different family of materials: 1) RPt compounds which follow the De Gennes Law, allowing us to determine the values of the effective mass m * and exchange constant. 2) The compounds RNi2Si2 in which it is possible to establish a relationship between the magnetic resistivity and the magnetic structures. 3) The compounds CeyLa1-yNixPt1-x, in which we study the Kondo effects. 4) The amorphous Co1-x(Fe5Ni5)x)75Si15B10 metals, in which there is a minimum in the resistivity at low temperatures as well as variations in LnT, T2 and T at low, intermediate and high temperatures respectively.