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Despite its relevance to metal\u2013hydrogen interactions and magnetically driven elasticity, the extensive investigation of this phase is almost limited to room temperature. Here, we performed x-ray diffraction measurements at high pressure and high temperature, identifying the singularity in the temperature\u2013volume relationship as the Curie temperature (TC). Pressurization lowered the TC of dhcp-FeHx and produced pronounced volume anomalies, indicating that pressure enhanced magnetoelastic coupling. Density functional theory combined with dynamical mean-field theory (DFT + DMFT) reproduced the spontaneous magnetization and its negative pressure dependence of TC, consistent with our experimental results. This establishes a methodology for determining magnetic transition temperatures and magnetoelastic coupling effects and highlights dhcp-FeHx as a unique model system for providing new insights into itinerant-electron magnetism.<\/jats:p>","DOI":"10.1063\/5.0340829","type":"journal-article","created":{"date-parts":[[2026,7,7]],"date-time":"2026-07-07T13:16:46Z","timestamp":1783430206000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":1,"title":["Pressure-induced thermal expansion anomalies in dhcp iron hydride associated with magnetoelastic coupling"],"prefix":"10.1063","volume":"165","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-5441-9945","authenticated-orcid":false,"given":"Yuichiro","family":"Mori","sequence":"first","affiliation":[{"name":"Graduate School of Science, The University of Tokyo 1 , 7\u20133\u20131 Hongo, Bunkyo-ku, Tokyo 113\u20130033,","place":["Japan"]},{"name":"The Department of Earth and Planetary Science, Faculty of Arts and Sciences, Yale University 2 , New Haven, Connecticut 06511,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0000-5968-4062","authenticated-orcid":false,"given":"Katsutoshi","family":"Aoki","sequence":"additional","affiliation":[{"name":"Graduate School of Science, The University of Tokyo 1 , 7\u20133\u20131 Hongo, Bunkyo-ku, Tokyo 113\u20130033,","place":["Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8587-1213","authenticated-orcid":false,"given":"Hiroyuki","family":"Kagi","sequence":"additional","affiliation":[{"name":"Graduate School of Science, The University of Tokyo 1 , 7\u20133\u20131 Hongo, Bunkyo-ku, Tokyo 113\u20130033,","place":["Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0008-2463-7280","authenticated-orcid":false,"given":"Masahiro","family":"Takano","sequence":"additional","affiliation":[{"name":"Graduate School of Science, The University of Tokyo 1 , 7\u20133\u20131 Hongo, Bunkyo-ku, Tokyo 113\u20130033,","place":["Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0161-711X","authenticated-orcid":false,"given":"Ina","family":"Park","sequence":"additional","affiliation":[{"name":"Center for Computational Quantum Physics (CCQ), Flatiron Institute 3 , New York, New York 10010,","place":["USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0003-4841-2952","authenticated-orcid":false,"given":"Zifan","family":"Wang","sequence":"additional","affiliation":[{"name":"Center for High Pressure Science and Technology Advanced Research 4 , Shanghai 201203,","place":["People\u2019s Republic of China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0765-6374","authenticated-orcid":false,"given":"Duck Young","family":"Kim","sequence":"additional","affiliation":[{"name":"Center for High Pressure Science and Technology Advanced Research 4 , Shanghai 201203,","place":["People\u2019s Republic of China"]},{"name":"Division of Advanced Nuclear Engineering, Pohang University of Science and Technology 5 , Pohang 37673,","place":["Republic of Korea"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9242-2240","authenticated-orcid":false,"given":"Noriyoshi","family":"Tsujino","sequence":"additional","affiliation":[{"name":"Japan Synchrotron Radiation Research Institute, SPring-8 6 , 1\u20131\u20131 Kouto, Sayo-cho, Sayo-gun, Hyogo 679\u20135198,","place":["Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7838-4065","authenticated-orcid":false,"given":"Sho","family":"Kakizawa","sequence":"additional","affiliation":[{"name":"Japan Synchrotron Radiation Research Institute, SPring-8 6 , 1\u20131\u20131 Kouto, Sayo-cho, Sayo-gun, Hyogo 679\u20135198,","place":["Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4221-8783","authenticated-orcid":false,"given":"Yuji","family":"Higo","sequence":"additional","affiliation":[{"name":"Japan Synchrotron Radiation Research Institute, SPring-8 6 , 1\u20131\u20131 Kouto, Sayo-cho, Sayo-gun, Hyogo 679\u20135198,","place":["Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"317","published-online":{"date-parts":[[2026,7,7]]},"reference":[{"key":"2026070709132653500_c1","volume-title":"The Metal-Hydrogen System: Basic Bulk Properties","year":"2006"},{"key":"2026070709132653500_c2","doi-asserted-by":"publisher","first-page":"104430","DOI":"10.1103\/physrevb.86.104430","article-title":"Hydrogen-induced modification of the electronic structure and magnetic states in Fe, Co, and Ni monohydrides","volume":"86","year":"2012","journal-title":"Phys. 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