Invar behavior and negative thermal expansion linked to magnetic transition in dhcp iron hydride under high pressure conditions
Yuichiro Mori, Katsutoshi Aoki, Masahiro Takano, Hiroyuki Kagi, Ina Park, Zifan Wang, Duck Young Kim, Noriyoshi Tsujino, Sho Kakizawa, Yuji Higo
公開日: 2025/1/15
Abstract
Hydrogen incorporation into iron interstitial sites under high-pressure conditions forms iron hydride with a double hexagonal close-packed (dhcp) structure. This phase is stable over a broad pressure-temperature range and exhibits a pressure-induced ferromagnetic-paramagnetic transition. In this study, we revealed that dhcp iron hydride exhibits the Invar-like behaviour and its thermal expansion becomes negative at elevated pressures by X-ray diffraction. Our findings, supported by DFT+DMFT calculations, demonstrate that these anomalous volume changes are governed by magnetic transitions. Notably, the experimentally determined magnetic volume contribution is an order of magnitude smaller than previous theoretical predictions.