In situ synchrotron 57Fe Mössbauer spectroscopy of RFe2 (R = Y, Gd) hydrides synthesized under ultra-high-pressure hydrogen

•We report the high pressure Mössbauer studies of C15 Laves RFe2 (R = Y, Gd) hydrides.•Two-step magnetic transition was found in C15 Laves RFe2 under high pressure H2.•Pressure induced magnetic transition of RFe2 hydride was not affected by R atom.

In situ synchrotron radiation 57Fe Mössbauer spectroscopy was used to study the C15 Laves phases RFe2 (R = Y, Gd) under ultra-high-pressure hydrogen in a diamond anvil cell. In both cases, the 57Fe isomer shift showed a rapid increase at a few GPa, and once again showed a small increase at above P ∼ 10 GPa. The quadrupole splitting also showed stepwise changes. As a marked effect, a two-step magnetic transition was clearly observed for RFe2 (R = Y, Gd). The results indicate that two different hydride phases appear in the RFe2–H reaction system under the hydrogen pressure (up to 34 GPa).