Study of magnon mode characteristics in solid oxygen by high resolution spectroscopy

The higher energetic magnon at 27 cm-1 was systematically investigated by far-IR-absorption and Raman scattering in α-O2 (T = 11-24 K). The softening of the magnon frequency - described in mean field theory - can be explained by a weakening of the exchange interaction due to thermal expansion and by a loss of magnetic order due to thermal fluctuations. Bandwidth as a function of temperature can be fitted by a power law, with a zero bandwidth at T = 0 K (Γ = aT4.4). Dephasing processes via magnon-magnon scattering are the only meaningful relaxation mechanisms of this magnon mode. The integrated band intensity, normalized to our low temperature value, directly follows the spin-spin correlation function and describes the long range magnetic order parameter in α-O2. The spectral characteristics, band frequency and band intensity (ω and I) prove that the α - β phase transition (at Tαβ = 23.8 K) is not purely magnetic