Reaching the equilibrium spin structure of Ca₃Co₂O₆ Ising triangular frustrated magnet at low temperatures

Understanding the observed metastable magnetization steps vs magnetic field with very slow dynamics in Ca₃Co₂O₆ Ising triangular frustrated magnet poses a long-standing challenge. We make a step forward in solving this puzzle by conducting a detailed study of the ground state of this spin system in temperatures below 4 K. Our work shows that the ground state can be reached at low temperatures by cooling down Ca₃Co₂O₆ single crystal in fields ranging from 0.125T to 3.6T oriented parallel to its easy-magnetization axis. Through this procedure we achieve a predicted ground state at 2 K and explore stability of this state by time-relaxation measurements. We do not however succeed in approaching the ground state with quantum annealing in transverse magnetic fields of up to 7 T, likely due to the large Ising anisotropy of the Co spins. We compare our equilibrium experimental data for Ca₃Co₂O₆ spin system to the quantum Monte Carlo simulations of a modified version of the Axial Next-Nearest-Neighbor Ising (ANNNI) model. This modified ANNNI model is derived for Ca₃Co₂O₆ by interleaving three chains to form one effective spin chain with frustrated nearest, next-nearest and next-next-nearest neighbor interactions.