Magnetic Field Dependence of the Hall effect in the Frustrated Magnet UNi₄B

The strongly correlated material UNi₄B contains a hexagonal uranium lattice with noncollinear and frustrated magnetic order below 20 K and at zero magnetic field. Only two-thirds of the uranium moments order while the remaining one-third form a paramagnetic chain perpendicular to the hexagonal lattice. The originally proposed zero-field toroidal moment arrangement, however, has been questioned in several recent studies, and the high-field magnetic ordering remains undetermined. Further, when a magnetic field is applied along perpendicular directions within the hexagonal plane, UNi₄B shows distinct magnetic transitions due to small distortions that lower the symmetry from hexagonal to orthorhombic. Here, we report the Hall resistivity of UNi₄B, collected with a magnetic field up to 16 T applied along the principal orthorhombic axes. We discuss magnetic phases where the response deviates from the ordinary Hall effect and the corresponding symmetry implications for the magnetic order of UNi₄B. Additional insights into the magnetic properties of UNi₄B are provided by neutron scattering data.