Crossover Phase Diagram of 2D Heisenberg Ferro- and Antiferromagnets

We propose a single crossover phase diagram applicable to 2D collinear Heisenberg antiferromagnets (AFMs) and ferromagnets (FMs), and show that the scaling regimes of AFMs and FMs are in one-to-one correspondence. The phase diagram is split into classical and quantum regions. Our two key results are: (i) in the classical region, the AFMs and FMs exhibit nearly identical behavior near their respective ordering wavevectors, which we observe for S=1 and higher using series expansions; and (ii) in the quantum region, quantum critical (QC) regime is present not only for the AFMs, but for FMs as well.