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

Comprehensive magnetic-field-temperature ($H$-$T$) phase diagram of solid oxygen including the $θ$ 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 $S_θ\sim S_α<S_β<<S_γ$.