Anomalous Magnetothermopower in a Metallic Frustrated Antiferromagnet

We report the temperature \(T\) and magnetic field \(H\) dependence of the thermopower \(S\) of an itinerant triangular antiferromagnet PdCrO\(_2\) in high magnetic fields up to 32 T. In the paramagnetic phase, the zero-field thermopower is positive with a value typical of good metals with a high carrier density. In marked contrast to typical metals, however, \(S\) decreases rapidly with increasing magnetic field, approaching zero at the maximum field scale for \(T >\) 70 K. We argue here that this profound change in the thermoelectric response derives from the strong interaction of the 4\(d\) correlated electrons of the Pd ions with the short-range spin correlations of the Cr\(^{3+}\) spins that persist beyond the N\'{e}el ordering temperature due to the combined effects of geometrical frustration and low dimensionality.