Change of antiferromagnetic structure near a quantum critical point in CeRh1-xCoxIn5

The elastic neutron-scattering experiments were carried out on the solid solutions CeRh1-xCoxIn5 to clarify the nature of the antiferromagnetic (AF) state in the vicinity of the quantum critical point: x(c)similar to 0.8. The incommensurate AF order with the wave vector of q(h)=(1/2,1/2,similar to 0.3) observed in pure CeRhIn5 is weakly suppressed upon doping with Co, and a commensurate q(c)=(1/2,1/2,1/2) and an incommensurate q(1)=(1/2,1/2,similar to 0.42) AF structures evolve at intermediate Co concentrations. The AF orders with q(c) and q(1) are enhanced at x=0.7, and furthermore, the q(h) AF order vanishes. These results suggest that the AF correlations with the q(c) and q(1) modulations are significantly enhanced in the intermediate x range, and may be connected with the evolution of the superconductivity observed above x similar to 0.3.