Complex conductivity of UTX compounds in high magnetic fields

We have performed rf-skin depth (complex-conductivity) and magnetoresistance measurements of antiferromagnetic UTX compounds (T=Ni and X=Al, Ga, Ge) in applied magnetic fields up to 60 T applied parallel to the easy directions. The rf penetration depth was measured by coupling the sample to the inductive element of a resonant tank circuit and then, measuring the shifts in the resonant frequency Δf of the circuit. Shifts in the resonant frequency Δf are known to be proportional to the skin depth of the sample and we find a direct correspondence between the features in Δf and magnetoresistance. Several first-order metamagnetic transitions, which are accompanied by a drastic change in Δf, were observed in these compounds. In general, the complex-conductivity results are consistent with magnetoresistance data.