Development of an energy-domain 57Fe-Mossbauer spectrometer using synchrotron radiation and its application to ultrahigh-pressure studies with a diamond anvil cell

An energy-domain Fe-57-Mossbauer spectrometer using synchrotron radiation (SR) with a diamond anvil cell (DAC) has been developed for ultrahigh-pressure measurements. The main optical system consists of a single-line pure nuclear Bragg reflection from an oscillating (FeBO3)-Fe-57 single crystal near the Neel temperature and an X-ray focusing device. The developed spectrometer can filter the Doppler-shifted single-line Fe-57-Mossbauer radiation with a narrow bandwidth of neV order from a broadband SR source. The focused incident X-rays make it easy to measure a small specimen in the DAC. The present paper introduces the design and performance of the SR Fe-57-Mossbauer spectrometer and its demonstrative applications including the newly discovered result of a pressure-induced magnetic phase transition of polycrystalline (Fe3BO6)-Fe-57 and an unknown high-pressure phase of (GdFe2)-Fe-57 alloy placed in a DAC under high pressures up to 302 GPa. The achievement of Mossbauer spectroscopy in the multimegabar range is of particular interest to researchers studying the nature of the Earth's core.