Compression and magnetic properties of Fe-Si alloys at high pressure

Abstract:

The Earth’s core is considered to be mainly composed of Fe. Since the density of the core is smaller than that of pure Fe under the core conditions, the core has been considered to contain light elements. Si is one of the most important light elements in the core. Although the phase relations and compression behaviors of Fe-Si alloys 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 and structural transitions in the Fe-Si alloys, we made simultaneous measurements of X-ray diffraction and synchrotron Mössbauer spectroscopy of the Fe-Si alloys up to 40 GPa at room temperature. The Fe-Si alloys used for the measurements have compositions with Fe_0.95Si_0.05 and Fe_0.88Si_0.12 enriched in ⁵⁷Fe. The starting material was synthesized by melting of 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. Our Mössbauar data together with X-ray diffraction data revealed that the transition from magnetic to non-magnetic phase occurs at 18 GPa simultaneously with the transition from bcc to hcp phase in Fe_0.95Si_0.05. Moreover, the transition pressure increases with increasing the Si content in the alloys. The present results imply that the changes in physical properties such as sound velocity and compression are caused not only by the structural change from bcc to hcp but also by the magnetic transition from magnetic to nonmagnetic.