Structure and magnetism of the triangular lattice material YbBO₃

YbBO₃is a member of the orthoborate family of materials which contains a triangular arrangement of Yb³⁺ions. Here we study the physical properties of YbBO₃with neutron diffraction, inelastic neutron scattering, specific heat, and ac susceptibility measurements. The neutron diffraction measurements confirm that our samples of YbBO₃crystallize in the monoclinic space groupC2/c(#15) which contains two crystallographically distinct Yb³⁺sites decorating a slightly distorted triangular lattice. Heat capacity and ac susceptibility measurements indicate a potential transition to magnetic order at 0.4 K. In agreement with these observations, neutron diffraction measurements at 0.044 K observe magnetic Bragg peaks which can be indexed by a propagation vector of (0 0 1). Although determining a unique spin configuration corresponding to the observed magnetic Bragg peaks is not possible, model refinements indicate that the ordered moments are likely in the range of 0.4-0.9 μBand, notably, require moments on both Yb sites. In addition to the magnetic Bragg peaks, diffuse scattering at lowQis observed indicating that the transition does not correspond to complete long range magnetic order. The two-site picture for YbBO₃is further evidenced by the number of crystal field excitations observed by inelastic neutron scattering measurements. Together these results show that YbBO₃is a two-site triangular lattice material with signatures of long-range order as well as shorter ranged spin correlations.