Magnetic Ordering in Solid Oxygen up to Room Temperature

magnetic ordering under high pressure in the � (‘‘orange’’) phase, i.e., in the range 6–8 GPa and 20–240 K. We show that � -O2 contains in total three different magnetic structures, all of them being antiferromagnetic and differing in the stacking sequence of O2 sheets along the c axis. This structural diversity can be explained by the quasi-two-dimensional nature of � -O2 and the strong orientation dependence of the magnetic exchange interaction between O2 molecules. The results show that � -O2 is a room temperature antiferromagnet.