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

Abstract

We have performed electron spin resonance (ESR) measurements on single crystals of the newly synthesized Mn layered oxide Rb 4 Mn(MoO 4 ) 3 , in which Mn 2+ 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 N1 , T N2 , T N1 < T 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 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 Rb 4 Mn(MoO 4 ) 3 is a quasi-2D HTAFM with Ising aniso...