The local atomic and magnetic structures of the compounds AMnO2 (A = Na, Cu), which realize a geometrically frustrated, spatially anisotropic triangular lattice of Mn spins, have been investigated by atomic and magnetic pair distribution function analysis of neutron total scattering data. Relief of frustration in CuMnO2 is accompanied by a conventional cooperative symmetry-lowering lattice distortion driven by N\'eel order. In NaMnO2, however, the distortion has a short-range nature. A cooperative interaction between the locally broken symmetry and short-range magnetic correlations lifts the magnetic degeneracy on a nanometer length scale, enabling long-range magnetic order in the Na-derivative. The degree of frustration, mediated by residual disorder, contributes to the rather differing pathways to a single, stable magnetic ground state in these two related compounds. This study demonstrates how nanoscale structural distortions that cause local-scale perturbations can lift the ground state degeneracy and trigger macroscopic magnetic order.
@article{arxiv.2001.09917,
title = {Nanoscale degeneracy lifting in a geometrically frustrated antiferromagnet},
author = {Benjamin A. Frandsen and Emil S. Bozin and Eleni Aza and Antonio Fernandez Martinez and Mikhail Feygenson and Katharine Page and Alexandros Lappas},
journal= {arXiv preprint arXiv:2001.09917},
year = {2020}
}