Understanding complex magnetic order in disordered cobalt hydroxides through analysis of the local structure

TL;DR

This study reveals how local structural disorder in cobalt hydroxides leads to complex magnetic behavior, despite an overall antiferromagnetic order, by analyzing local polyhedral arrangements and their magnetic contributions.

Contribution

It introduces a detailed local structural analysis method that explains magnetic properties in disordered cobalt hydroxides beyond traditional unit-cell descriptions.

Findings

Local structure analysis explains magnetic loops despite antiferromagnetic order.

Aperiodic cobalt coordination polyhedra account for uncompensated magnetic moments.

Quantitative agreement achieved between local structure model and magnetic measurements.

Abstract

In many ostensibly crystalline materials, unit-cell-based descriptions do not always capture the complete physics of the system due to disruption in long-range order. In the series of cobalt hydroxides studied here, Co(OH)$_{2-x}$(Cl)$_x$(H$_2$O)$_{n}$, magnetic Bragg diffraction reveals a fully compensated N\'eel state, yet the materials show significant and open magnetization loops. A detailed analysis of the local structure defines the aperiodic arrangement of cobalt coordination polyhedra. Representation of the structure as a combination of distinct polyhedral motifs explains the existence of locally uncompensated moments and provides a quantitative agreement with bulk magnetic measurements and magnetic Bragg diffraction.