Study on postcritical homo-transition mechanism for zero hysteresis and innovation of multiferroic shape-change materials

2023 Fiscal Year Final Research Report

• Project/Area Number: 20K20544
• Research Category: Grant-in-Aid for Challenging Research (Pioneering)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 26:Materials engineering and related fields
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: Hosoda Hideki 東京工業大学, 科学技術創成研究院, 教授 (10251620)
• Project Period (FY): 2020-07-30 – 2024-03-31
• Keywords: 臨界状態 / 相変移 / ホモ遷移挙動 / 磁性形状記憶合金 / 単結晶 / 複合材料 / アクチュエーター / 磁歪

Outline of Final Research Achievements

The postcritical homo transition represents a phase transition occurring within the supercritical state between solid phases. Although The postcritical homo transition in the supercritical state does not entail a phase transformation, it involves changes in phase states. Then, this can be potentially suitable as sensors and actuators, particularly for high-speed applications. In this research, we have mainly used magnetic shape memory alloys of NiFeCoGa and NiMnGa, to reveal the phase transitions and to develop advanced sensor/actuator composite materials. For NiFeCoGa, this phenomenon is only observed when compressed along the crystalline orientation parallel to [001]. Besides, we have explored other materials showing similar behavior, as well as to create composite materials based on NiMnGa alloy particles for giant magnetostrain.

Free Research Field

材料工学

Academic Significance and Societal Importance of the Research Achievements

機能変換材料は、機能と形状変化が対応するマルチフェロイック材料であり、デバイス性能の飛躍が期待できる。この機能が相変態による物性値の変化で起こる場合、相変態に伴う熱の出入りや界面の発生により速度の制限や寿命に限界がある。しかし、これが超臨界状態で起こる場合、相変態が消失し、熱の出入りや界面が無くなる。これをポストクリティカル（臨界点以降）状態といい、相変態なしで状態変異するためホモ遷移という。材料全体が中間状態を遷移して相変移すれば、ヒステリシス損が無くなり、超伝導のようにロスのない究極の機能変換が達成できる。この基礎学理の解明は学術的価値があり、本機能を持つ材料は工学的に社会に貢献できる。