The magneto-structural relationship in the tetrahedral spin chain oxide CsCoO$_2$

TL;DR

This study explores the structural and magnetic properties of CsCoO$_2$, revealing a high-temperature antiferromagnetic order and complex low-temperature relaxation phenomena linked to bond angle bifurcation.

Contribution

It combines experimental and computational methods to elucidate the magneto-structural relationship in CsCoO$_2$, highlighting the impact of bond angle bifurcation on magnetic interactions.

Findings

CsCoO$_2$ exhibits AFM order at 424 K.

No magnetic structure change at 100 K, despite structural transition.

Bond angle bifurcation weakens AFM interactions along chains.

Abstract

We have investigated the structural and magnetic transitions in CsCoO$_2$ using calorimetric measurements, neutron powder diffraction (NPD), density functional theory (DFT) calculations and muon-spin relaxation ($\mu$SR) measurements. CsCoO$_2$ exhibits three-dimensional long-range antiferromagnetic (AFM) order at 424~K, resulting in antiferromagnetic alignment of chains of ferromagnetically ordered Co-Co spin dimers. Although there is no change in magnetic structure around a structural transition at $T^{*}=100$~K, the resulting bifurcation of corner-shared Co--O--Co bond angles causes a weakening of the AFM interaction for one set of bonds along the chains. Consequently, the system undergoes a complex freezing out of relaxation processes on cooling.