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 $\mathrm{U}{\mathrm{Ni}}_4\mathrm{B}$. 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: $a=6.963\left(4\right)$, $b=14.793\left(9\right)$, $c=17.126\left(8\right)$ Å]. We determine the magnetically ordered structure, concluding that below $T_{\mathrm{N}}=19.5\mathrm{K}$, 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 $330\mathrm{mK}$, 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 $\mathrm{U}{\mathrm{Ni}}_4\mathrm{B}$ previously unresolved.

• Received 12 April 2021
• Accepted 18 May 2021

DOI:https://doi.org/10.1103/PhysRevB.103.184426