Anisotropic resistivity and giant magnetoresistance in UNi2Ge2 and UNiGa from ab initio calculations

The zero-temperature resistivity in UNi2Ge2 and UNiGa is investigated theoretically using density-functional bandstructure theory and the linear-response approach for calculating the static resistivity for the antiferromagnetic (AF) and ferromagnetic (F) phases, from which the magnetoresistance (MR) is computed. The resistivity in the AF ground-state of UNi2Ge2 is calculated to be quite anisotropic, i.e. ρ parallel /ρ perpendicularto ∼2.1, with ρ parallel, ρ perpendicularto the resistivities for current parallel, respectively, perpendicular to the c-axis. For some Fermi surface sheets, however, extremely large resistivity anisotropies of ∼10-40 are found. A substantial anisotropic MR of (Δρ/ρ) parallel =-61 % and (Δρ/ρ) perpendicularto =-14 % is predicted. We compare the predicted MR in UNi2Ge2 to that of UNiGa, for which we obtain even larger MR values of (Δρ/ρ) parallel =-64 % and (Δρ/ρ) perpendicularto =-45 %. The basic mechanism of the MR is, in both compounds, identified to be a superzone Fermi surface reconstruction at the metamagnetic transition. (orig.)