Crystal structure of frustrated antiferromagnet UNi4B

Crystal structure of a frustrated antiferomagnet UNi4B was investigated precisely by the X-ray diffraction on a Czochralski-grown high-quality single crystal. The unit cell was unambiguously determined as ortborhombic with the lattice parameters a = 6.968, b = 17.1377, and c = 14.8882 angstrom. These orthorhombic lattice parameters are approximately related to the reported hexagonal unit cell parameters a(hex) and C-hex as a = 2c(hex), b = 2 root 3a(hex) and c = 3a(hex). They are also consistent with the previously reported weak superlattice reflections measured by the neutron scattering assuming the hexagonal lattice. We have found that four different uranium sites with the different local environment exist. Therefore UNi4B can no more be regarded as a pure frustrated system as previously assumed and its magnetic properties should be reanalyzed based on the correct structure. (c) 2007 Elsevier B.V. All rights reserved.