Magnetic structure and phase diagram in a spin-chain system: Ca$_3$Co$_2$O$_6$

TL;DR

This paper investigates the magnetic structures and phase transitions in the frustrated spin-chain compound Ca$_3$Co$_2$O$_6$, revealing how entropy influences the crossover between different magnetic phases.

Contribution

It provides a theoretical analysis of the magnetic phase diagram of Ca$_3$Co$_2$O$_6$ based on the 2D Ising model on a triangular lattice, explaining the entropy-driven phase crossover.

Findings

Identification of low-temperature magnetic structure as ground state of 2D Ising model

Discovery of a crossover at 12 K driven by entropy in disordered chains

Formulation of general rules for phase diagrams of frustrated Ising chain systems

Abstract

The low-temperature structure of the frustrated spin-chain compound Ca$_3$Co$_2$O$_6$ is determined by the ground state of the 2D Ising model on the triangular lattice. At high-temperatures it transforms to the honeycomb magnetic structure. It is shown that the crossover between the two magnetic structures at 12 K arises from the entropy accumulated in the disordered chains. This interpretation is in an agreement with the experimental data. General rules for for the phase diagram of frustrated Ising chain compounds are formulated.