# $H$-$T$ phase diagram of solid oxygen

## TL;DR

This paper presents a detailed $H$-$T$ phase diagram of solid oxygen, including the $ heta$ phase, derived from ultrahigh-field and magnetocaloric effect measurements, revealing entropy relations among phases.

## Contribution

It provides the first comprehensive $H$-$T$ phase diagram of solid oxygen including the $ heta$ phase, addressing experimental challenges and clarifying phase entropy relations.

## Key findings

- Phase diagram includes the $ heta$ phase.
- Entropy relation: $S_ heta o S_eta o S_eta o S_eta o S_eta$.
- Addresses experimental issues like non-equilibrium and MCE effects.

## Abstract

Comprehensive magnetic-field-temperature ($H$-$T$) phase diagram of solid oxygen including the $\theta$ phase is discussed in the context of the ultrahigh-field measurement and the magnetocaloric effect (MCE) measurement. The problems originating from the short duration of the pulse field, non-equilibrium condition and MCEs, are pointed out and dealt with. The obtained phase diagram manifests the entropy relation between the phases as $S_\theta \sim S_\alpha<S_\beta<<S_\gamma$.