High-pressure neutron diffraction study on -FeOOH; The Spin-reorientation transition and hydrogen-bond symmetrization

Ikeda, Osamu*; Yamamoto, Hajime*; Sano, Asami   ; Sakamaki, Tatsuya*; Kuribayashi, Takahiro*; Noda, Yukio*; Suzuki, Akio*

The compression behavior of iron oxyhydroxide -FeOOH is complex, with variations in its magnetic property and bonding character. In this study, in situ powder neutron diffraction experiments were conducted on -FeOOH and -FeOOD up to pressures exceeding 20 GPa to investigate a spin-reorientation transition, hydrogen-bond symmetrization, and their correlation. The magnetic transition was observed at 8 GPa in both -FeOOH and -FeOOD. The crystal symmetry and H-bonds of -FeOOH transitioned from P21nm with asymmetric H-bonds to Pnnm with disordered H-bonds at 17.90 GPa, while -FeOOD remained asymmetric. The pressure evolution of the interatomic angles and distances indicates that the coordinate geometry of Fe transitioned toward H-bond symmetrization and would have affected the magnetic anisotropy.