A study of pressure-induced phase transformation on Ni-based Heusler compounds

2021 Fiscal Year Final Research Report

• Project/Area Number: 18K04685
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 26010:Metallic material properties-related
• Research Institution: Kurume Institute of Technology
• Principal Investigator: Eto Tetsujiro 久留米工業大学, 工学部, 教授 (70322295)
• Project Period (FY): 2018-04-01 – 2022-03-31
• Keywords: 強磁性形状記憶合金 / ホイスラー合金 / Ni2MnGa / マルテンサイト変態 / 磁歪 / 相図 / 高圧 / x線構造解析

Outline of Final Research Achievements

We have studied structure, transport, magnetic composition, and pressure dependence of ferromagnetic Ni-based Whistler alloy. A Ni2+xMnGa1-x sample was prepared and a magnetic-structural phase transition with a huge magnetic calorific effect was observed in non-stoichiometric compositions. In addition, a pre-martensite transformation with large magnetostriction at 0 degrees Celsius or higher was observed, which will lead to the realization of a super-magnetostriction near room temperature.
Furthermore, X-ray diffraction measurement under high pressure was performed at　radiation facility. We succeeded in observing a pressure-induced structural phase transition of Ni2MnGa for the first time in the world. By analyzing the crystal structure and elastic modulus of the high-pressure phase, we were able to obtain important findings regarding direct relationship between the lattice constant, interatomic distance, and crystal structure, and the electronic state and magnetism.

Free Research Field

固体物理学

Academic Significance and Societal Importance of the Research Achievements

Ni2MnGaに代表される強磁性ホイスラー合金は、形状記憶効果、磁歪、磁気冷凍等の新機能材料として注目されており、実用化により機械部品の小型化、および省エネルギー化が可能となる。本研究より、マルテンサイト変態や双晶磁歪の巨視的現象に関して結晶構造や電子・磁気特性などの微視的視点から新しい知見が得られたことは、物性物理学における学術研究に寄与する。
また、得られた成果は低温に留まっている構造変態点を室温近傍に上昇させるための研究指針を与えるものとなる。今後、高圧相の結晶構造や体積弾性率等の結果をバンド計算へ反映することで、合金の組成や添加元素の最適化に向けて高精度なフィードバックが可能となる。