Metastable antiphase boundary ordering in CaFe2O4

CaFe2O4 is an S=5/2 antiferromagnet exhibiting two magnetic orders that 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, elucidating the microscopic spin Hamiltonian. In doing so, we suggest that the low-temperature A phase order (↑⏐↑⏐⏐↓⏐↓) finds its origins in the freezing of antiphase boundaries created by thermal fluctuations in a parent B phase order (↑⏐⏐↓↑⏐⏐↓). The low-temperature magnetic order observed in CaFe2O4 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.