Emergence of novel phase of solid oxygen in ultrahigh magnetic Held

Faraday discovered the magnetism of molecular oxygen in 1850, and since then, oxygen has attracted significant interests as a ubiquitous but exotic molecular magnet. In solid oxygen, the magnetic energy through the exchange interaction is comparable to the van der Waals cohesive energy, resulting in a strong spin-lattice correlation. We reported the discovery of a magnetic-field-induced phase transition of solid oxygen using ultrahigh magnetic fields up to 186 T. This is the first experiments demonstrating the phase control through the spin by applying a magnetic field. Magneto-optical absorption measurements of the α phase at low temperatures revealed that visible light absorption suddenly ceases and the background transparency dramatically improves above the critical field. The large hysteresis in these data indicates a first-order transition with a relaxation time on the order of microseconds. The results strongly suggest the reconstruction of the O₂ molecular geometry by the magnetic field, which causes that the antiferromagnetic phase collapses and the field-induced phase should have an isotropic crystal structure. Since all of the known phases of O₂ are induced in high pressure, the discovery of a field-induced phase is noteworthy in the long history of solid O₂ studies.