Absence of itinerant-electron ferromagnetism in LaRh6B4

Contrary to previous studies which reported itinerant-electron ferromagnetism for La${\mathrm{Rh}}_6$ ${\mathrm{B}}_4$ at 6 K, no evidence for ferromagnetism is found for high-purity La${\mathrm{Rh}}_6$ ${\mathrm{B}}_4$ in the ac susceptibility down to 40 mK and in the static magnetization down to 3 K. It would seem probable that the "ferromagnetism" reported previously for this compound was not intrinsic but arose from too high a concentration of magnetic impurities. Similar studies on Ce${\mathrm{Rh}}_6$ ${\mathrm{B}}_4$, Y${\mathrm{Rh}}_6$ ${\mathrm{B}}_4$, and Lu${\mathrm{Rh}}_6$ ${\mathrm{B}}_4$ fail to find any evidence for either ferromagnetism or superconductivity above 40 mK.