Collinear ordering of easy-axis triangular lattice antiferromagnets

Antiferromagnetically coupled moments on the frustrated triangular lattice typically order in a coplanar state at low temperature. Here, we demonstrate that the presence of not-very-large easy axis single ion anisotropy leads to an interesting orientationally ordered collinear state in triangular lattice antiferromagnets with moments $S \ge 3/2$. This ordered state breaks the symmetry of $\pi/3$ rotations about a lattice site, while leaving intact the translational symmetry of the lattice.