high pressure
An energy-domain 57Fe-Mössbauer 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 57FeBO3 single crystal near the Néel temperature and an X-ray focusing device. The developed spectrometer can filter the Doppler-shifted single-line 57Fe-Mössbauer 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 57Fe-Mössbauer spectrometer and its demonstrative applications including the newly discovered result of a pressure-induced magnetic phase transition of polycrystalline 57Fe3BO6 and an unknown high-pressure phase of Gd57Fe2 alloy placed in a DAC under high pressures up to 302 GPa. The achievement of Mössbauer spectroscopy in the multimegabar range is of particular interest to researchers studying the nature of the Earth's core.