Incommensurate antiferromagnetism in the intermetallic superconductor HoNi2B2C

We report high-resolution x-ray and neutron-scattering studies of the antiferromagnetism of the rare-earth superconductor, HoNi2B2C (T-C=8.5 K). At low temperatures, T<5 K, the superconductivity coexists with a long-range ordered, commensurate Neel state. In the incommensurate antiferromagnetic state, 5 K<T<7 K, we find two phase coexistence between an a-axis modulation and a c-axis basal plane spiral-like structure. The c-axis structure is characterized by two wave vectors. Short-range ordered fluctuations of the commensurate phase, observed for T>5 K, are interpreted in terms of local strains.