Incommensurate magnetic modulations in the magnetic superconductor HoNi2B2C

Full text: The borocarbide HoNi2B2C is an unconventional superconductor of particular interest, since long-range magnetism coexists and competes with superconductivity on a common energy range [1]. Our study is based on high quality single crystals of 11B-substituted HoNi2B2C. The neutron diffraction investigations are devoted to two issues of specific relevance to HoNi2B2C. Firstly, the near re-entrant phase between 5K<T<6K which is characterized by the commensurate-incommensurate competition of different magnetic structures. Secondly, starting from the anti ferromagnetically ordered state at 2K we observed incommensurate magnetic modulations of the title compound stabilized as a function of the applied magnetic field. Comprehensive single-crystal neutron diffraction for an applied magnetic field in different directions stresses the richness of the system under investigation and revealed that the magnetic phase diagram of HoNi2B2C is more complicated than proposed so fare [2]. Furthermore we performed a spherical neutron polarimetry experiment to determine the two ICM magnetic structures of HoNi2B2C and neutron spectroscopy investigations to obtain the microscopic magnetic coupling parameters. All these studies resulted in quite a consistent and complete picture of magnetism in HoNi2B2C, however, we could not find clear evidence for a strong interaction between superconductivity and magnetism. (author)