Electron Spin Resonance in the Quasi-Two-Dimensional Triangular-Lattice Antiferromagnet Rb4Mn(MoO4)3

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We have performed electron spin resonance (ESR) measurements on single crystals of the newly synthesized Mn layered oxide Rb4Mn(MoO4)3, in which Mn2+ ions with S = 5/2 form an equilateral triangular-lattice. The magnetic properties of this compound are reported to be well reproduced by theoretical calculations in a two-dimensional Heisenberg triangular-lattice antiferromagnet (2D HTAFM) with Ising anisotropy. The compound exhibits two successive phase transitions (T_{\text{N1}}, T_{\text{N2}}, T_{\text{N1}} < T_{\text{N2}}) at zero-field. We have successfully explained the observed frequency dependence of the ESR resonance fields and the reported magnetization curves parallel and perpendicular to the easy-axis and the c-axis, at T < T_{\text{N1}} by mean-field approximation and a classical Monte Carlo simulation using a spin Hamiltonian of the 2D HTAFM with Ising anisotropy. Then, we have evaluated the anisotropy and exchange constants accurately. Consequently, we have confirmed that Rb4Mn(MoO4)3 is a quasi-2D HTAFM with Ising anisotropy.
2011-06-15