Magnetic spin-flop transition of ε-FeOOH at 8 GPa

Moessbauer spectra of polycrystallineε-⁵⁷FeOOH were measured up to 14.6 GPa at room temperature using the energy-domain synchrotron ⁵⁷Fe Moessbauer source at BL11XU in SPring-8. Based on measurements with/without an external magnetic field,ε-FeOOH appears to be antiferromagnetic at ambient pressure and temperature. On compression, the quadrupole shift 2ε shifted from negative to positive at ∼8 GPa, which is consistent with a magnetic spin rotation. Previous XRD studies did not detect any transitions at this pressure; thus we infer the change in 2ε to be the third pressure-induced transition without major structural change in addition to the hydrogen-bond symmetrization and electronic spin transition. (author)