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

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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References in corpus (5)

• Spin Dynamics of the Spin-1/2 Kagome Lattice Antiferromagnet ZnCu_3(OH)_6Cl_2
• Continuous excitations of the triangular-lattice quantum spin liquid YbMgGaO4
• Magnetic Phase Diagram of the S=1/2 Triangular-Lattice Heisenberg Antiferromagnet Ba3CoNb2O9
• Detection of XY behaviour in weakly anisotropic quantum antiferromagnets on the square lattice
• Ba8CoNb6O24: a spin-1/2 triangular-lattice Heisenberg antiferromagnet in the 2D limit