[S-MP47_1PO1] Physics and Chemistry of Minerals

[SMP47-P05] Study of physical properties of Fe-Si alloy at high pressureusing using synchrotron radiation Mossbauer spectroscopy

*Nanami SUZUKI¹, Eiji OHTANI¹, Naohisa HIRAO², Seiji KAMADA¹, Maki HAMADA³, Tatsuya SAKAMAKI¹, Yasuo OHISHI², Ryo MASUDA⁴, Takaya MITSUI⁵ (1.Department of Earth and planetary materials science, Graduate School of Science, 2.Japan Synchrotron Radiation Research Institute, Hyogo, 679-5198, Japan, 3.School of Natural System, College of Science and Engineering, Kanazawa University, Kanazawa, 920-119, 4.Research Reactor Institute, Kyoto University, Osaka, 590-0494, Japan, 5.Japan Atomic Energy Agency, Hyogo, 679-5148, Japan)

The Earth's core is divided into the liquid outer core and solid inner core based on seismological observations. The Earth's core has been geochemically and cosmochemically thought to be mainly composed of Fe. The density of the core is smaller than that of pure iron under the core conditions. Therefore, the core has been considered to contain light elements, such as H, S, Si, C, and O. Si is one of the most important light elements in the core. Although the phase relations and compression behaviors in the Fe-Si alloy have been studied at high pressure and temperature in order to investigate properties of the inner core, magnetic properties of the alloys have not been studied well. In order to clarify the relationship between the magnetic transition and the structural transition of the Fe-Si alloy, we made simultaneous measurements of X-ray diffraction and synchrotron Mössbauer spectroscopy of the Fe-Si alloy up to 40 GPa at room temperature. The Fe-Si alloy used for the measurements has a composition of Fe_0.95Si_0.05 enriched with ⁵⁷Fe. The starting material was synthesized by melting the mixture of ⁵⁷Fe and Fe-Si alloys under the Ar-H₂ atmosphere by laser heating. Mössbauer spectra and XRD patterns were obtained at the beamlines, BL10XU and BL11XU of SPring-8 up to 40 GPa at room temperature. Our Mössbauer data together with X-ray diffraction data revealed that the magnetic transition from magnetic to non-magnetic phase occurs at 18 GPa simultaneously with the bcc to hcp transition. The change in the sound velocity and compression behavior of the Fe-Si alloy has been reported associated with the structural transformation of the alloy from bcc to hcp. The present results imply that the change in these physical properties is caused not only by the structural change but also by the magnetic transition.