Crystal structure of frustrated antiferromagnet UNi4B

Abstract Crystal structure of a frustrated antiferomagnet UNi 4 B was investigated precisely by the X-ray diffraction on a Czochralski-grown high-quality single crystal. The unit cell was unambiguously determined as orthorhombic with the lattice parameters a = 6.968 , b = 17.1377 , and c = 14.8882 A . These orthorhombic lattice parameters are approximately related to the reported hexagonal unit cell parameters a hex and c hex as a = 2 c hex , b = 2 3 a hex and c = 3 a 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 UNi 4 B 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.