Extended infrared absorption spectroscopy study of the magnetic properties of solid oxygen at high-pressure and low-temperature

The antiferromagnetic alpha and delta phases of solid oxygen have been investigated by means of infrared absorption spectroscopy along several isotherms, decreasing pressure at several temperatures, in the pressure range from 0.6 to 9.1 GPa between 30 and 298 K. The path followed in the P-T plane also crosses the recently proposed hypothetical phase boundary between the antiferromagnetic delta-I phase and the nonmagnetic delta-II phases. No evidence of this phase transition has been observed in the spectra and, more importantly, strong evidence of antiferromagnetic ordering of the molecular spins has been observed in the region assigned to the nonmagnetic delta-II phase.