Magnetic phase diagram, critical behavior, and two-dimensional to three-dimensional crossover in the triangular lattice antiferromagnet RbFe(MoO4)2

We have studied the magnetic and thermodynamic properties as well as the NMR spectra of the quasi-two-dimensional (quasi-2D) Heisenberg antiferromagnet RbFe(MoO4)(2). The observed temperature dependence of the order parameter, the critical indices, and the overall magnetic H-T phase diagram are all in a good agreement with the theoretical predictions for a 2D XY model. The temperature dependence of the specific heat at low temperature demonstrates a crossover from a T (2) law characteristic of a two-dimensional antiferromagnet to a three-dimensional T (3) law. (c) 2006 American Institute of Physics.