Low-temperature magnetic behaviour on the triangular lattice in hexagonal Ba$_3$Tb(BO$_3$)$_3$

TL;DR

This study investigates the low-temperature magnetic properties of Ba$_3$Tb(BO$_3$)$_3$, revealing no long-range order and suggesting a singlet ground state with weak XY anisotropy due to geometric frustration on a triangular lattice.

Contribution

It provides the first detailed experimental and theoretical analysis of magnetic frustration and ground state characteristics in Ba$_3$Tb(BO$_3$)$_3$ on a quasi-2D triangular lattice.

Findings

No magnetic order down to 75 mK and 1.5 K.

Ground state is a singlet with a low-lying doublet.

Tb ions exhibit weak XY single-ion anisotropy.

Abstract

The hexagonal polymorph of Ba$_3$Tb(BO$_3$)$_3$ contains Tb$^{3+}$ ions on a quasi-2D triangular lattice, resulting in geometric magnetic frustration. Powder samples of Ba$_3$Tb(BO$_3$)$_3$ have been investigated using specific heat, powder neutron diffraction (PND), inelastic neutron scattering (INS) and muon-spin relaxation spectroscopy ($\mu$SR). No long-range magnetic ordering is observed down to the lowest measured temperatures of 75 mK in PND and specific heat data and 1.5 K in the $\mu$SR data. Modelling the INS spectrum using a point charge model suggests that the ground state is a singlet with a low-lying doublet on each of the two crystallographically independent Tb$^{3+}$ sites and that both the Tb ions display weak XY single-ion anisotropy.