Explaining Magnetization and Hysteresis limit cycles in CCO with spin graphs

Calcium Cobalt Oxide Ca3Co2O6 (CCO) is known to exhibit stair-step magnetization jumps when exposed to an external magnetic field at low temperatures. As the field is swept, three magnetization plateaus of width H~1.2T emerge before saturation. These plateaus can be explained by treating the system as a frustrated 2D antiferromagnetic triangular Ising model, but many unexplained features persist: Notably, we find that CCO displays hysteric limit cycles when magnetic fields are repeatedly swept across plateau boundaries, and sudden magnetization jumps beyond the usual plateaus when fields are swept quickly. We explain these features through a novel mapping of the metastable spin states in the model Hamiltonian to distinct graph structures among spins anti-aligned with the applied field.