Antiferromagnetic solid oxygen studied by positive muons

We present a zero magnetic field muon spin rotation study of α-O2 (antiferromagnetic phase of solid oxygen) in the temperature range of 10-24 K. Static magnetic order has been observed below the α-β transition temperature (Tαβ = 23.8 K). The temperature dependence of the muon precession frequency exhibits behavior characteristic of a two-dimensional Heisenberg spin-1 system with the anisotropy parameter α ∼ 10-2 quite similar to that of antiferromagnetic phase of the high-temperature superconductor parent compounds. A unique local field at the muon site has been determined to be B0 = 1.27(5) kG at low temperatures. (orig.)