Magnetic order in hedenbergite: CaFeSi2O6

Synthetic hedenbergite orders antiferromagnetically at 38 K although the principal interactions are ferromagnetic, between Fe²⁺ ions in the Ml chains of edge-sharing octahedra. The susceptibility follows a Curie-Weiss law above 100 K with θ = 35 K and p_eff = 4.98 μ_B. A fit of the 4.2 K Mossbauer spectrum yields a positive, near-axial electric field gradient and a hyperfine field of 18.8 T. The likely magnetic structure consists of ferromagnetic chains, each weakly coupled antiparallel to its four c-centred equivalents.