Figure 1: Properties of the model Hamiltonian.
From: Critical exponents and scaling invariance in the absence of a critical point
(a) Sketch of some equilibrium magnetization curves m(T, b) as a function of the applied field b theoretically expected for an unfrustrated ferromagnet below Tc (black lines). The equilibrium curves are described coming from large fields, as indicated by arrows. Note the jump when b=0 is crossed for T<Tc, highlighted by dots. A pictorial curve representing the paramagnetic behaviour, T>Tc, is also displayed (red line). (b) Two ground-state configurations (linked by the 
symmetry) of the model defined by Hamiltonian (1) in the absence (g=0) and (c) in the presence (g≠0) of frustration. (d) Sketch of some equilibrium magnetization curves m as a function of the applied field b for a frustrated system at different temperatures (blue lines). The discontinuity expected in the unfrustrated case at b=0 gives way to a linear behaviour, as a result of the frustrating effect of dipolar interaction. The red line is the same as in the plot a.
