Magnetic structure of solid oxygen in the vicinity of the <i>α</i>-<i>β</i> transition point

The stability of the collinear antiferromagnetic structure of solid α-O2 against changes in the parameter ϰ = J3/J1 (J3 and J1 are the constants of the intra- and inter-sublattice exchange interaction between two nearest neighbors from the same basal plane) is investigated. It is shown that the collinear two-sublattice structure is stable for 0 &amp;lt; ϰ &amp;lt; 1/2. A second-order phase transition to a helical magnetic structure whose period in the direction of the monoclinic axis is, generally speaking, incommensurable with the lattice constant occurs at the point ϰ = 1/2. The pitch of the helix in this direction is equal to φ = 2 arccos (2ϰ)−1. A continuous transition to a triangular structure with φ = 2π/3 occurs at the point ϰ = 1. According to the estimates obtained, the helical phase exists in a narrow neighborhood of the α–β transition point (ΔT ≈0.2°K).

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