Ce-Site Dilution in the Ferromagnetic Kondo Lattice CeRh_6Ge_4

The heavy fermion ferromagnet CeRh_6Ge_4 is the first example of a clean stoichiometric system where the ferromagnetic transition can be continuously suppressed by hydrostatic pressure to a quantum critical point. In order to reveal the outcome when the magnetic lattice of CeRh_6Ge_4 is diluted with non-magnetic atoms, this study reports comprehensive measurements of the physical properties of both single crystal and polycrystalline samples of La_xCe_1-xRh_6Ge_4. With increasing x, the Curie temperature decreases, and no transition is observed for x > 0.25, while the system evolves from exhibiting coherent Kondo lattice behaviors at low x to the Kondo impurity scenario at large x. Moreover, non-Fermi liquid behavior is observed over a wide doping range, which agrees well with the disordered Kondo model for 0.52 \leq x \leq 0.66, while strange metal behavior is revealed in the vicinity of x_\rm c = 0.26.