Magnon Raman scattering in solid oxygen under high pressure

Pressure and temperature dependence of magnon and libron Raman peaks of solid oxygen was studied at pressures from 0 to 4 GPa and temperatures from 1.8 to 110 K. Tn 1.8 K, the magnon peak shifts continuously toward higher energy with increasing pressure and disappears around 2.9 GPa, which means that antiferromagnetic character continues at least up to 2.9 GPa. Pressure coefficients of the magnon energy change at 0.07 and 1.3 GPa which suggests the occurrence of a slight change in spin arrangement in the antiferromagnetic phase. The determined coefficients are 12.8 (0-0.07 GPa), 11.8 (0.07-1.3 GPa), and 8.1 cm(-1)/GPa (1.3-2.9 GPa). With increasing temperature, the magnon peak disappears by 7-10K lower than the alpha-beta phase boundary at the pressure lower than 1 GPa. The vanishing temperature becomes nearly constant (around 40 K) at higher pressure regions. It suggests that a new spin arrangement different from the alpha phase is realized before the transition to the beta phase occurs.