Probing quantum criticality in ferromagnetic CeRh₆Ge₄

CeRh 6 Ge 4 is unusual in that its ferromagnetic transition can be suppressed continuously to zero temperature, i.e., to a ferromagnetic quantum -critical point (QCP), through the application of modest hydrostatic pressure. This discovery has raised the possibility that the ferromagnetic QCP may be of the Kondo-breakdown type characterized by a jump in Fermi volume, to which thermopower S measurements should be sensitive. Though S / T changes both sign and magnitude around the critical pressure P c approximate to 0 . 8 GPa, these changes are not abrupt but extend over a pressure interval from within the ferromagnetic state up to P c . Together with temperature and pressure variations in electrical resistivity and previously reported heat capacity, thermopower results point to the near coincidence of two sequential effects near P c , delocalization of 4 f degrees of freedom through orbitalselective hybridization followed by quantum criticality of itinerant ferromagnetism.