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arXiv · 1905.01049

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

R. Rawl·L. Ge·Z. Lu·Z. Evenson·C. R. Dela Cruz·Q. Huang·M. Lee·E. S. Choi·M. Mourigal·H. D. Zhou·J. Ma
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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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R. Rawl, L. Ge, Z. Lu, Z. Evenson, C. R. Dela Cruz, Q. Huang, M. Lee, E. S. Choi, M. Mourigal, H. D. Zhou, J. Ma. 2019-05-30. Ba8MnNb6O24: a model two-dimensional spin-5/2 triangular lattice antiferromagnet. https://doi.org/10.1103/physrevmaterials.3.054412

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