Thermodynamics of two-dimensional quantum magnets with collinear order parameter

We review recent theoretical investigations of the thermodynamics of two-dimensional quantum magnets on bipartite lattices. Despite the simple, semiclassical nature of the ground state, different types of low temperature scaling can occur in these systems. None of these scaling proposals allows for a conclusive description of experimental and numerical data. However, these are well reproduced assuming a wide nonuniversal crossover region smoothly connected to the high temperature limit. This provides evidence that for a quantitative description of experimental results and numerical data at finite temperatures nonuniversal effects are much more important then previously thought.