Magnetic Correlations in the Triangular Antiferromagnet TbInO$_3$

TbInO$_3$ crystallizes with a hexagonal $P6_3cm$ structure in which layers of edge-sharing triangles of magnetic Tb$^{3+}$ ions are separated by non-magnetic [InO$_5$]$^{7-}$ units. TbInO$_3$, therefore, realizes an excellent opportunity to explore the behavior of a two-dimensional magnetic triangular lattice, a canonical model of geometric frustration. Here we present our study of a polycrystalline sample of TbInO$_3$. Our high resolution powder neutron diffraction data (HRPD, ISIS) of TbInO$_3$ confirm that the triangular layers of Tb$^{3+}$ remain undistorted to at least $0.46$ K. Magnetic susceptibility data follow Curie-Weiss behavior over a wide range of $T$ with ${\theta}=-17.19(3)$ K indicating the dominance of antiferromagnetic correlations. The susceptibility data also show an absence of conventional long-range spin order down to at least $0.55$ K, reflecting the frustrated nature of TbInO$_3$. Elastic magnetic diffuse neutron scattering (SEQUOIA, SNS) is observed below ${\sim}15$ K, due to the presence of static two-dimensional spin correlations. The spectrum of crystal field excitations in TbInO$_3$ appears to have an exotic form due to the existence of two crystallographically distinct Tb$^{3+}$ sites and leads to a strong Ising anisotropy of the spin symmetry.