Phonon-modulated magnetic interactions and spin Tomonaga-Luttinger liquid in the p-orbital antiferromagnet CsO2

TL;DR

This paper investigates the complex magnetic behavior of CsO2, revealing how lattice vibrations and orbital ordering influence spin interactions, leading to a Tomonaga-Luttinger liquid state and demonstrating CsO2 as a model for molecular magnetic solids.

Contribution

It uncovers the coupling between spin, lattice, and orbital degrees of freedom in CsO2, highlighting the transition from a square lattice to spin chains and the emergence of a spin liquid state.

Findings

Nonmonotonic temperature dependence of exchange coupling above Ts1

Observation of spin Tomonaga-Luttinger-liquid behavior below Ts1

Identification of p-orbital ordering effects on magnetic interactions

Abstract

The magnetic response of antiferromagnetic CsO2, coming from the p-orbital S=1/2 spins of anionic O2- molecules, is followed by 133Cs nuclear magnetic resonance across the structural phase transition occuring at Ts1=61 K on cooling. Above Ts1, where spins form a square magnetic lattice, we observe a huge, nonmonotonic temperature dependence of the exchange coupling originating from thermal librations of O2- molecules. Below Ts1, where antiferromagnetic spin chains are formed as a result of p-orbital ordering, we observe a spin Tomonaga-Luttinger-liquid behavior of spin dynamics. These two interesting phenomena, which provide rare simple manifestations of the coupling between spin, lattice and orbital degrees of freedom, establish CsO2 as a model system for molecular solids.