Magnetic ground states of CeRu2Si2-xGex alloys

CeRu2Si2 is a heavy-fermion compound which has a non-magnetic ground state, while CeRu2Ge2 is a ferromagnet below 9 K. The magnetic properties of CeRu2Si2-xGex alloys have been studied using a combination of neutron powder diffraction, single crystal susceptibility and high-field magnetisation measurements. The large magnetic anisotropy found in these alloys is shown to arise from the crystal field which leaves an isolated vertical stroke ± 5/2 > doublet ground state. Antiferromagnetism is found for x as small as 0.1, confirming that CeRu2Si2 is on the verge of magnetic order. The onset of order has a dramatic effect on the metamagnetic transition found in high fields. (orig.)