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Structure and magnetism of the triangular lattice material YbBO3

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Journal of Physics: Condensed Matter
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YbBO3 is a member of the orthoborate family of materials which contains a triangular arrangement of Yb3+ ions. Here we study the physical properties of YbBO3 with neutron diffraction, inelastic neutron scattering, specific heat, and ac susceptibility measurements. The neutron diffraction measurements confirm that our samples of YbBO3 crystallize in the monoclinic space group $C2/c$ (#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 $\mu_\text{B}$ and, notably, require moments on both Yb sites. In addition to the magnetic Bragg peaks, diffuse scattering at low Q is observed indicating that the transition does not correspond to complete long range magnetic order. The two-site picture for YbBO3 is further evidenced by the number of crystal field excitations observed by inelastic neutron scattering measurements. Together these results show that YbBO3 is a two-site triangular lattice material with signatures of long-range order as well as shorter ranged spin correlations.