Metastable antiphase boundary ordering in CaFe$_{2}$O$_{4}$

TL;DR

This study models neutron scattering data of CaFe₂O₄, revealing how competing interactions and thermal fluctuations lead to metastable antiphase boundary ordering in its magnetic phases.

Contribution

It introduces a Green's function formalism to elucidate the microscopic spin Hamiltonian and explains the origin of low-temperature A phase order as metastable boundary freezing.

Findings

Identification of the microscopic spin Hamiltonian for CaFe₂O₄

Explanation of the metastable A phase origin from boundary freezing

Demonstration of competition between exchange coupling and anisotropy

Abstract

CaFe$_{2}$O$_{4}$ is an $S=5/2$ antiferromagnet exhibiting two magnetic orders which shows regions of coexistence at some temperatures. Using a Green's function formalism, we model neutron scattering data of the spin wave excitations in this material, ellucidating the microscopic spin Hamiltonian. In doing so, we suggest that the low temperature A phase order $(\uparrow\uparrow\downarrow\downarrow)$ finds its origins in the freezing of antiphase boundaries created by thermal fluctuations in a parent B phase order $(\uparrow\downarrow\uparrow\downarrow)$. The low temperature magnetic order observed in CaFe$_{2}$O$_{4}$ is thus the result of a competition between the exchange coupling along $c$, which favors the B phase, and the single-ion anisotropy which stabilizes thermally-generated antiphase boundaries, leading to static metastable A phase order at low temperatures.