The superconducting and ferromagnetic phase boundaries in the (Er1-xHox)Rh4B4 mixed ternary alloy system meet in a multicritical point at xcr ≈ 0.9. For xcr, the compounds first become superconducting as the temperature is lowered, and then lose superconductivity in a transition to ferromagnetism. The coexistence of superconductivity and ferromagnetism for alloys near the erbium-rich end of the phase diagram is well established. It has also been suggested that ferromagnetism and superconductivity coexist in alloys with x just below xcr. We have carried out neutron-diffraction, ac magnetic susceptibility, and heat-capacity measurements on a sample of (Er0.16Ho0.84)Rh4B4 to investigate the possibility of coexistence of ferromagnetism and superconductivity for x ≈ xcr. We find that there are minor discrepancies in the superconducting and magnetic transition temperatures reported for different samples of (Er0.16Ho0.84)Rh4B4, but that ferromagnetism and superconductivity do occur simultaneously over a narrow temperature range in this sample. We suggest that an inhomogeneous state occurs, consisting of separate ferromagnetic and superconducting regions, rather than microscopic coexistence
