Reaching the equilibrium state of frustrated triangular Ising magnet Ca3Co2O6

TL;DR

This study investigates the magnetic equilibrium state of Ca3Co2O6, a frustrated Ising magnet, using field-cooling and quantum annealing, successfully reaching the predicted 1/3 magnetization and aligning experiments with simulations.

Contribution

The paper demonstrates that field-cooling can reach the equilibrium state in Ca3Co2O6, and compares quantum annealing effects with Monte Carlo simulations, advancing understanding of frustrated magnet ground states.

Findings

Field-cooling achieves the predicted 1/3 magnetization.

Quantum annealing shows no measurable effect up to 7 T.

Simulations agree well with experimental results.

Abstract

Ca3Co2O6 is a frustrated magnet consisting of a triangular arrangement of chains of Ising spins. It shows regular magnetization steps vs magnetic field every 1.2 T that are metastable with very slow dynamics. This has puzzled the community for many years and given rise to numerous potential theories. Here we approach the problem by seeking the elusive magnetic equilibrium state at T = 2 K. To this end, we explore two approaches: (1) bypassing the slow dynamics produced by changing fields by instead field-cooling directly to the target temperature, and (2) quantum annealing in transverse magnetic fields. While we observe no measurable effect of the quantum annealing in fields up to 7 T, which is likely due to the large Ising anisotropy of Co spins in this material, we find that for the field cooling in longitudinal fields we achieve the predicted equilibrium 1/3 magnetization. We perform Monte Carlo simulations of the ground state phase diagram and we also simulate the quantum annealing process and find good agreement between experiment and theory. Thus we present an investigation of the elusive ground state properties of the canonical frustrated triangular system Ca3Co2O6.