Magnetoelastic nature of solid oxygen epsilon-phase structure

TL;DR

This paper reveals that the epsilon-phase of solid oxygen has a magnetoelastic structure stabilized by strong antiferromagnetic exchange interactions, explaining its unique crystal structure and distinguishing it from other phases.

Contribution

It provides a new explanation for the epsilon-phase's structure based on magnetic interactions and magnetoelastic forces, resolving long-standing structural mysteries.

Findings

Epsilon-phase's structure is stabilized by antiferromagnetic exchange interactions.

Magnetoelastic forces cause transformation of O2 molecule arrangements.

Distinction between epsilon-phase and other phases due to magnetic stabilization.

Abstract

For a long time a crystal structure of high-pressure epsilon-phase of solid oxygen was a mistery. Basing on the results of recent experiments that have solved this riddle we show that the magnetic and crystal structure of epsilon-phase can be explained by strong exchange interactions of antiferromagnetic nature. The singlet state implemented on quaters of O2 molecules has the minimal exchange energy if compared to other possible singlet states (dimers, trimers). Magnetoelastic forces that arise from the spatial dependence of the exchange integral give rise to transformation of 4(O2) rhombuses into the almost regular quadrates. Antiferromagnetic character of the exchange interactions stabilizes distortion of crystal lattice in epsilon-phase and impedes such a distortion in long-range alpha- and delta-phases.