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Abstract:
Classical spin systems with non-coplanar ground states typically exhibit nonlinear magnetization curves characterized by kinks and jumps. Our article briefly summarizes the most important related analytical results. In a comprehensive case study, we then address AF-square kagome and AF/FM-square kagome spin lattices equipped with additional cross-plaquette interactions. It is known that these systems have non-coplanar ground states that assume a cuboctahedral structure in the absence of a magnetic field. When a magnetic field H is switched on, a rich variety of different phases develops from the cuboctahedral ground state, which are studied in their dependence on H and a cross-plaquette coupling constant J (3) > 0 . For the AF square-kagome spin lattice, we carefully identify and describe seven phases that appear in a phase diagram with five triple points. The transitions between these phases are predominantly discontinuous, although two cases exhibit continuous transitions. In contrast, the phase diagram of the AF/FM square-kagome model shows only four phases with a single triple point, but these also lead to exotic magnetization curves. Here, too, there are two types of phase boundaries belonging to continuous and discontinuous transitions.
