Transport properties in amorphous U_x-T_1-x films (T=Fe, Ni, Gd, Tb, and Yb) (invited)

Abstract

We describe the competing magnetic, localization, and phonon effects on the transport properties of amorphous magnetic UxT1-x films, with T=Fe, Ni, Gd, Tb, and Yb. Amorphous UxFe1-x films change from collinear to random ferromagnetism as x increases, and the temperature dependence of the resistivity denotes the competing effects of spin-flip and non-spin-flip exchange scattering processes. The resistivity has a minimum at Tf rising sharply below this temperature. The sign of the magnetic resistivity and the magnetoresistance indicates 〈Si ·Sj 〉>0, while the anisotropic magnetoresistance indicates a local exchange gap. Amorphous UxGd1-x and a-UxTb1-x are, respectively, spin glasses and random anisotropy dominated systems. The resistivity increases smoothly through T f and has a slight upturn at low temperatures that we associate with weak localization. The magnetoresistance is negative in both systems and the anisotropic magnetoresistance is null, although the applied field induces anisotropic behavior in the Tb containing films (asperomagnets). All samples show quadratic and positive field dependence of magnetoresistance well inside the paramagnetic regime, and a linear regime below Tf. At low temperatures and in the a-UxGd1-x films, negative (H) 1/2 and H2 regimes occur and are associated with weak localization processes dominated by the inelastic mean free path.