Probing quantum criticality in ferromagnetic CeRh6Ge4

${\mathrm{CeRh}}₆{\mathrm{Ge}}₄$ 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 ${\mathrm{P}}_c\ensuremath{\approx}0.8$ GPa, these changes are not abrupt but extend over a pressure interval from within the ferromagnetic state up to ${\mathrm{P}}_c$. 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 ${\mathrm{P}}_c$, delocalization of $4f$ degrees of freedom through orbital-selective hybridization followed by quantum criticality of itinerant ferromagnetism.