Successive phase transitions and phase diagrams for the quasi-two-dimensional easy-axis triangular antiferromagnet Rb₄Mn(MoO₄)₃

R. Ishii^1a, S. Tanaka¹, K. Onuma², Y. Nambu^3,4, M. Tokunaga¹, T. Sakakibara¹, N. Kawashima¹, Y. Maeno², C. Broholm^3,4, D. P. Gautreaux⁵, J. Y. Chan⁵ and S. Nakatsuji¹

¹ Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa - Chiba 277-8581, Japan
² Department of Physics, Kyoto University - Kyoto 606-8502, Japan
³ Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University Baltimore, MD 21218, USA
⁴ NIST Center for Neutron Research, National Institute of Standards and Technology (NIST) Gaithersburg, MD 20899, USA
⁵ Department of Chemistry, Louisiana State University - Baton Rouge, LA 70803, USA

^a rmorisaki@issp.u-tokyo.ac.jp

Received: 5 November 2010
Accepted: 3 March 2011

Abstract

Using magnetic, thermal and neutron measurements we show that Rb₄Mn(MoO₄)₃ is a quasi-2D triangular Heisenberg antiferromagnet with easy-axis anisotropy and successive transitions bracketing an intermediate collinear phase. An accurate quantitative account of the phase diagram is achieved through Monte Carlo simulation of a spin Hamiltonian with easy-axis anisotropy D=0.22J.