H-T phase diagram of solid oxygen

The 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, nonequilibrium conditions and MCEs, are pointed out and dealt with. The obtained phase diagram manifests the entropy relation between the phases as S_θ ∼ S_α < S_β << S_γ