Development of magnetic refrigerant materials in liquid H2 - liquid N2 temperature range by utilizing a first-order magnetic transition

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K05254
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 29010:Applied physical properties-related
• Research Institution: Kyushu University
• Principal Investigator: Wada Hirofumi 九州大学, 理学研究院, 教授 (80191831)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 磁気冷凍材料 / 磁気熱量効果 / 液体水素 / 一次相転移

Outline of Final Research Achievements

The purpose of the present study is development of magnetic refrigerant materials working in liquid H2 - liquid N2 temperature range. The target values of the magnetic entropy change and the thermal hysteresis are 30 J/ K kg and 1 K, respectively. We focused on Gd5Ge4, which undergoes a first-order magnetic transition (FOMT) from a ferromagnetic state to an antiferromagnetic state on heating. We succeed in developing magnetic refrigerant materials with the target values between 40 and 120 K by substituting Si for Ge. We noticed that the substitution of Si for Ge increases both the FOMT transition temperature and the magnetic entropy change. This is unusual, because the entropy change is expected to decrease, when the FOMT transition temperature is raised. We have successfully explained this behavior by taking account of temperature dependence of magnetic entropy change in both the ferromagnetic and antiferromagnetic states.

Free Research Field

磁性物理学

Academic Significance and Societal Importance of the Research Achievements

本研究ではあらたに低温で巨大磁気熱量効果を有する磁気冷凍材料を開発することができた．この結果は水素や天然ガスの液化に磁気冷凍を応用する上で大変有益であり，その意義は大きい．磁気冷凍材料に一次相転移を示す物質を使うという考えはわれわれによって提案されているが，これまで室温磁気冷凍材料の候補となる物質はすべて一次相転移物質であり，またその中で日本の寄与が大きいことは特筆される．また本研究では一次相転移温度が上昇するとき磁気エントロピー変化が増大するメカニズムも解明することができた．このことは今後の物質開発においても有用であり，その学術的意義も大きいといえる．