Raman spectroscopic investigations of the antiferromagnetic α phase of solid oxygen at low pressure (up to 1.25 GPa)

Abstract

Elementary magnon, libron and vibron excitations as well as combined two-libron excitations of solid α oxygen have been investigated by means of Raman scattering at several isobars in the pressure range up to 1.25 GPa. We deduced the band frequency, bandwidth and relative band intensity of all modes as a function of temperature and pressure. On the basis of these results we can exclude the possibility of all second-order phase transitions in the low temperature, low pressure range of oxygen stated in the literature. The disappearance of the sublattice magnetization σ could be estimated from the frequency of the higher energy magnon mode at the critical pressure ∼7.7 GPa which is in the vicinity of the phase transition from the antiferromagnetic ordered δ phase to the non-magnetic ε phase. The change of several spectroscopic features under increasing pressure clearly indicates that anharmonic contributions in the libron potential are altered.