Magnetotransport in Yb-based heavy fermion systems

We have performed magnetoresistance and Hall effect measurements on ternary Yb-based heavy fermion compounds: YbCu 4X (X=Ag, Au and Pd) and YbNiAl (gamma=350 mJ/molK 2, T N=2.3 K). For YbCu 4Ag the magnetoresistance is positive and shows a quadratic field dependence but is negative and s-shaped for YbCu 4Au and YbCu 4Pd. Measurements on YbNiAl under external pressure up to 2.0 GPa exhibit a stable magnetic ground state for this compound: The magnetoresistance depends weakly on pressure and we observe only a slight increase of T N with increasing pressure