The magnetism and elasticity of ε-FeOOH across the pressure-induced electronic spin transition

Abstract

We conducted in-situ synchrotron X-ray experiments on iron oxyhydroxide ε-FeOOH to study the effects of the pressure-induced electronic spin transition on magnetism and elasticity. Polycrystalline ε-FeOOH was compressed in diamond anvil cells, and Mossbauer spectra and inelastic X-ray scattering were measured up to 120 and 49.9 GPa, respectively. On compression, the Mossbauer spectra showed a transition from a single magnetic sextet to a single doublet with the coexistence region 30?48 GPa, suggesting the low-spin state without magnetic ordering. The longitudinal elastic wave velocity V L calculated using the acoustic phonon dispersion exhibited a ~5% decrease at 38 GPa, which is almost the middle of the coexistence pressure region observed by Mossbauer absorption, indicating an elastic softening by the spin transition. The V L drop would be attributed to the elastically soft low-spin domain inferred by the large pressure dependence of the center shift of the low-spin doublet.journal articl