Successive phase transitions and magnetization plateau in the spin-1 triangular-lattice antiferromagnet Ba2La2NiTe2O12 with small easy-axis anisotropy

The crystal structure and magnetic properties of the spin-1 triangular-lattice antiferromagnet ${\mathrm{Ba}}_{2}{\mathrm{La}}_{2}{\mathrm{NiTe}}_{2}{\mathrm{O}}_{12}$ are reported. Its crystal structure is trigonal $R\overline{3}$, which is the same as that of ${\mathrm{Ba}}_{2}{\mathrm{La}}_{2}{\mathrm{NiW}}_{2}{\mathrm{O}}_{12}$ [Y. Doi et al., J. Phys.: Condens. Matter 29, 365802 (2017)]. However, the exchange interaction $J/{k}_{\mathrm{B}}\ensuremath{\simeq}19$ K is much greater than that observed in the tungsten system. At zero magnetic field, ${\mathrm{Ba}}_{2}{\mathrm{La}}_{2}{\mathrm{NiTe}}_{2}{\mathrm{O}}_{12}$ undergoes successive magnetic phase transitions at ${T}_{\mathrm{N}1}=9.8$ K and ${T}_{\mathrm{N}2}=8.9$ K. The ground state is accompanied by a weak ferromagnetic moment. These results indicate that the ground-state spin structure is a triangular structure in a plane perpendicular to the triangular lattice owing to the small easy-axis-type anisotropy. The magnetization curve exhibits the one-third plateau characteristic of a two-dimensional triangular-lattice Heisenberg-like antiferromagnet. Exchange constants are also evaluated using density functional theory (DFT). The DFT results demonstrate the large difference in the exchange constants between tellurium and tungsten systems and the good two-dimensionality of the tellurium system.