paper

Ba8MnNb6O24: a model two-dimensional spin-5/2 triangular lattice antiferromagnet

arXiv:1905.01049 · doi:10.1103/PhysRevMaterials.3.054412

Abstract

We successfully synthesized and characterized the triangular lattice anitferromagnet Ba $_{8}$ MnNb $_{6}$ O $_{24}$ , which comprises equilateral spin-5/2 Mn $^{2 +}$ triangular layers separated by six non-magnetic Nb $^{5 +}$ layers. The detailed susceptibility, specific heat, elastic and inelastic neutron scattering measurements, and spin wave theory simulation on this system reveal that it has a 120 degree ordering ground state below T $_{N}$ = 1.45 K with in-plane nearest-neighbor exchange interaction ~0.11 meV. While the large separation 18.9 A between magnetic layers makes the inter-layer exchange interaction virtually zero, our results suggest that a weak easy-plane anisotropy is the driving force for the k $_{m}$ = (1/3 1/3 0) magnetic ordering. The magnetic properties of Ba $_{8}$ MnNb $_{6}$ O $_{24}$ , along with its classical excitation spectra, contrast with the related triple perovskite Ba $_{3}$ MnNb $_{2}$ O $_{9}$ , which shows easy-axis anisotropy, and the iso-structural compound Ba $_{8}$ CoNb $_{6}$ O $_{24}$ , in which the effective spin-1/2 Co $^{2 +}$ spins do not order down to 60 mK and in which the spin dynamics shows sign of strong quantum effects.

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