Magnetoresistance and de Haas-van Alphen Effect in U_<b>3</b>As_<b>4</b>and U_<b>3</b>P_<b>4</b>

Abstract

We measured the transverse magnetoresistance and de Haas-van Alphen (dHvA) oscillation in the ferromagnetic compounds U 3 As 4 and U 3 P 4 . The magnetoresistance in both compounds increases as a function of H n ( n ≃2) in a wide angular region, indicating that U 3 As 4 and U 3 P 4 are compensated metals. As for U 3 P 4 , the angular dependence of the magnetoresistance shows clearly dips for particular field directions. This implies the existence of a multiply-connected Fermi surface which favors open orbits along the <110> and <112> directions. We also detected several dHvA branches in U 3 As 4 and U 3 P 4 . Most of them are due to the closed Fermi surfaces, which are explained by recent results of fully relativistic spin-polarized LMTO band calculations. The cyclotron effective mass is large, ranging from 5 to 70 m 0 , and consistent with the electronic specific heat coefficient of 83 mJ/K 2 ·mol in U 3 As 4 and 90 mJ/K 2 ·mol in U 3 P 4 .