Structure and magnetism of a new hexagonal polymorph of Ba<inf>3</inf>Tb(BO<inf>3</inf>)<inf>3</inf> with a quasi-2D triangular lattice

This article reports the structural and magnetic characterisation of a new hexagonal (P63cm) low-temperature phase of Ba3Tb(BO3)3, isostructural with the heavier lanthanide borates with formula Ba3Ln(BO3)3 (Ln = Dy–Lu). The crystal structure contains a quasi-two-dimensional (2D) triangular lattice of Tb3+ ions and is predicted to display unusual magnetic behaviour as a result of the low dimensionality. Magnetic susceptibility χ(T) shows antiferromagnetic interactions (θCW = -7.15 K) and no sharp ordering transition at T ≥ 2 K, but analysis of Χ'(T), isothermal magnetisation and heat capacity suggests the possibility of short-range ordering at T ≈ 10 K. The material exhibits an inverse magnetocaloric effect at T < 4 K.EPSRC Strategic Equipment Grant EP/M000524/