Change of antiferromagnetic structure near a quantum critical point in CeRh1-x Cox In5

The elastic neutron-scattering experiments were carried out on the solid solutions CeRh1-x Cox In5 to clarify the nature of the antiferromagnetic (AF) state in the vicinity of the quantum critical point: xc ∼0.8. The incommensurate AF order with the wave vector of qh = (1/2,1/2,∼0.3) observed in pure CeRhIn5 is weakly suppressed upon doping with Co, and a commensurate qc = (1/2,1/2,1/2) and an incommensurate q1 = (1/2,1/2,∼0.42) AF structures evolve at intermediate Co concentrations. The AF orders with qc and q1 are enhanced at x=0.7, and furthermore, the qh AF order vanishes. These results suggest that the AF correlations with the qc and q1 modulations are significantly enhanced in the intermediate x range, and may be connected with the evolution of the superconductivity observed above x∼0.3.