Static and dynamical properties of the spin- 52 nearly ideal triangular lattice antiferromagnet Ba3MnSb2O9

We study the ground state and spin excitations in ${\mathrm{Ba}}_{3}{\mathrm{MnSb}}_{2}{\mathrm{O}}_{9}$, an easy-plane $S=5/2$ triangular lattice antiferromagnet. By combining single-crystal neutron scattering, electric spin resonance (ESR), and spin wave calculations, we determine the frustrated quasi-two-dimensional spin Hamiltonian parameters describing the material. While the material has a slight monoclinic structural distortion, which could allow for isosceles-triangular exchanges and biaxial anisotropy by symmetry, we observe no deviation from the behavior expected for spin waves in the in-plane ${120}^{\ensuremath{\circ}}$ state. Even the easy-plane anisotropy is so small that it can only be detected by ESR in our study. In conjunction with the quasitwo dimensionality, our study establishes that ${\mathrm{Ba}}_{3}{\mathrm{MnSb}}_{2}{\mathrm{O}}_{9}$ is a nearly ideal triangular lattice antiferromagnet with the quasiclassical spin $S=5/2$, which suggests that it has the potential for an experimental study of $Z$- or ${Z}_{2}$-vortex excitations.