Magnon Raman scattering in solid oxygen under high pressure

Pressure and temperature dependence of magnon and libron Raman peaks of sol id 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 ene rgy with increasing pressure and disappears around 2.9 GPa, which means tha t antiferromagnetic character continues at least up to 2.9 GPa. Pressure co efficients of the magnon energy change at 0.07 and 1.3 GPa which suggests t he occurrence of a slight change in spin arrangement in the antiferromagnet ic 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 m agnon peak disappears by 7-10K lower than the alpha-beta phase boundary at the pressure lower than 1 GPa. The vanishing temperature becomes nearly con stant (around 40 K) at higher pressure regions. It suggests that a new spin arrangement different from the alpha phase is realized before the transiti on to the beta phase occurs.