Abstract
We present an extensive powder and single-crystal neutron scattering investigation of the crystallographic structure and magnetic order of the frustrated metallic f-electron magnet UNi4B. We carry out a full refinement of the crystallographic structure and conclude that the low-temperature lattice symmetry is orthorhombic [space group Pmm2; cell parameters: a = 6.963(4), b = 14.793(9), c = 17.126(8) angstrom].
We determine the magnetically ordered structure, concluding that below T-N = 19.5 K, the material undergoes a transition into a partially ordered antiferromagnetic state. The magnetic structure is consistent with the existence of toroidal order in this material.
We further test the proposal of a second magnetic transition occurring at 330 mK, concluding that the thermodynamic anomalies observed at these temperatures do not reflect modifications of the magnetic structure. Our study provides a consistent picture of the interrelationship of structural and magnetic properties in the frustrated magnet UNi4B previously unresolved.