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

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Physical Review B
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We study the ground state and spin excitations in Ba3MnSb2O9, 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∘ state. Even the easy-plane anisotropy is so small that it can only be detected by ESR in our study. In conjunction with the quasi-two-dimensionality, our study establishes that Ba3MnSb2O9 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 Z2-vortex excitations.