Structure and magnetism of a new hexagonal polymorph of Ba$_3$Tb(BO$_3$)$_3$ with a quasi-2D triangular lattice

TL;DR

This study introduces a new hexagonal phase of Ba$_3$Tb(BO$_3$)$_3$ with a quasi-2D triangular lattice, revealing complex magnetic interactions and potential short-range order at low temperatures.

Contribution

It reports the discovery and structural characterization of a novel hexagonal polymorph of Ba$_3$Tb(BO$_3$)$_3$, highlighting its unique magnetic properties and low-dimensional lattice structure.

Findings

Antiferromagnetic interactions with $ heta_{CW} = -7.15$ K.

No sharp magnetic ordering above 2 K, but possible short-range order near 10 K.

Inverse magnetocaloric effect observed below 4 K.

Abstract

This article reports the structural and magnetic characterisation of a new hexagonal ($P6_3cm$) low-temperature phase of Ba$_3$Tb(BO$_3$)$_3$, isostructural with the heavier lanthanide borates with formula Ba$_3$Ln(BO$_3$)$_3$ (Ln = Dy-Lu). The crystal structure contains a quasi-two-dimensional (2D) triangular lattice of Tb$^{3+}$ ions and is predicted to display unusual magnetic behaviour as a result of the low dimensionality. Magnetic susceptibility $\chi(T)$ shows antiferromagnetic interactions ($\theta_{CW} = -7.15$ K) and no sharp ordering transition at $T \geq 2$ K, but analysis of $\chi'(T)$, isothermal magnetisation and heat capacity suggests the possibility of short-range ordering at $T \approx 10$ K. The material exhibits an inverse magnetocaloric effect at $T < 4$ K.