Antiferromagnetic transitions in high-T_c materials

The Neel ordering transition of the 2D spin-¹/₂ Heisenberg antiferromagnet is studied in the small in-plane anisotropy limit through extensive quantum Monte Carlo simulations on lattices as large as 96*96. At an Ising-like anisotropy energy h^A=0.0025, the system orders at T_c/kT=0.295. This striking effect and related results agree with a wide class of experiments and give some insight into these materials.