Phase Diagram of a Two-Dimensional Heisenberg Antiferromagnet in a Magnetic Field

Abstract

An analytical study is made on a two-dimensional classical isotropic Heisenberg antiferromagnet in a uniform magnetic field. This model is expected to show the Kosterlitz-Thouless phase transition due to a XY-like degeneracy of a canted spin-flop ground state. It is shown that the transition temperature approaches zero logarithmically as the field approaches zero.