Helimagnetism in CrBr$_2$ and CrIBr

TL;DR

This study reveals that CrBr$_2$ and CrIBr are helimagnetic materials with temperature-dependent magnetic structures, expanding understanding of helimagnetism in layered chromium halides and showing how anion substitution influences magnetic angles.

Contribution

It demonstrates helimagnetism in CrBr$_2$ and CrIBr, and shows how the helical angle varies with Br substitution, providing new insights into magnetic interactions in these compounds.

Findings

CrBr$_2$ and CrIBr are helimagnetic with Neel temperatures of 17 K and 12 K.

The helical angle increases with Br substitution, from 89.7° to 147°.

Intermediate magnetic transitions are observed in both compounds.

Abstract

In CrX$_2$ (X=Br, I), a Jahn-Teller effect distorts the octahedral configuration of the anions about Cr, resulting in a "ribbon chain" structure. We previously observed helimagnetism in CrI$_2$ propagating along the ribbon chains, with an 80-90$^{\circ}$ rotation per Cr ion. Via neutron scattering, we report that CrBr$_2$ and the solid solution CrIBr are also helimagnetic, with N\'{e}el temperatures of 17 and 12 K, respectively, and signs of intermediate magnetic transitions in both compounds. The helical angle between spins on consecutive Cr ions along the ribbon chains increases with increasing Br substitution, from 89.7$^{\circ}$ (CrI$_2$) to 116$^{\circ}$ (CrIBr) to 147$^{\circ}$ (CrBr$_2$), possibly as a result of decreasing longer-range intrachain spin interactions with the increased electron localization of the lighter anions.