巨磁热材料的相变调控和负热膨胀行为研究

The discovery of new type giant magnetocaloric material with strong magneto-lattice coupling has greatly promoted the development of magnetic refrigeration technology at high temperature and even around room temperature. The phase transition and lattice effect dominated by magnetic atoms in these materials provide a natural platform for the study of negative thermal expansion materials. The objective of this proposal is to develop novel multifunctional negative thermal expansion (NTE) materials with largely tunable NTE coefficient working in a wide temperature region through investigating the key physical and material factors that control the magnetostructural transition and magneto-lattice coupling, so as to meet the urgent demand for thermal compensation materials in the advanced industries. Through systematically investigating the effect of the introduction of chemical and physical pressure and magnetic atomic defects on the phase transition nature/width and spin-lattice coupling in the giant magnetocaloric materials, we can understand the key reason that regulates the magnetostructural transition and NTE behavior, and get the methodology that regulates NTE characteristics from atomic scale. Through our researches in this project, (1) we will overall understand the general rules of NTE effect of giant magnetocaloric materials and get the effective methodology that regulates magnetocaloric effect, NTE coefficient, and broaden the phase transition window; (2) Through systematically studying strain effect, defects, and composition regulated electronic structure and dynamics of phase transition, we can clarify the evolution rule of phase transition and relative machanism, and eventually guide practical applications.

具有强磁晶耦合的新型巨磁热材料的发现极大地推动了高温乃至室温区磁制冷技术的发展。这些材料所具有的由磁性原子主导的相变和晶格效应为负热膨胀材料的研究提供了天然平台。本项目拟通过深入研究调控相变和磁晶耦合的物理和材料因素，开发可工作于宽温区、负热膨胀系数大幅可调的新型多功能负热膨胀材料，以满足快速发展的新兴制造业对热补偿材料的迫切需求。通过系统研究化学压力、物理压力、磁性原子缺陷的引入对相变性质/宽度、自旋序-晶格序耦合的影响，认识调控磁共结构相变和负热膨胀行为的关键诱因，从原子尺度获得调控负热膨胀性质的多自由度手段。通过本项研究，希望（1）全面认识巨磁热材料负热膨胀效应的一般规律，找到调控巨磁热效应、负热膨胀系数和拓宽温跨的多途径调控方法。（2）通过系统研究应力场、缺陷、组分调控的电子结构和相变动力学过程及背后的物理根源，揭示相变调控机理，阐明不同体系相变演化规律和诱因，指导实际应用。

材料的磁热效应和反常热膨胀性质（负热膨胀NTE，零膨胀ZTE）在固态制冷和精密制造业具有重要应用，是凝聚态物理和材料科学领域的热点研究内容之一。具有强磁晶耦合的巨磁热材料体系由磁性原子主导的相变和晶格效应为负热膨胀材料的研究提供了极佳平台。本项目系统研究了多种材料体系的磁热效应和负热膨胀、零膨胀性质，揭示了相关机理和基本规律，为相关领域的应用提供了材料基础。主要成果包括：..1.在具有巨磁热效应的MM’X体系，首次利用非公度螺旋磁结构主导的晶格畸变实现了巨大负热膨胀，在磁热Gdx(Dy0.5Ho0.5)1-xCo2合金中实现了宽温区超低热膨胀。（Mater.Horiz. 2020:7, 804-810；Script Mater. 2020: 185, 181）.2.首次利用电场调控的应力记忆效应实现了对FeRh/PMN-PT磁热材料滞后损耗的非易失性调控。解决了样机设计中遇到的双场循环瓶颈问题。（Nano Energy 2019:59, 285-294）.3.在具有自主知识产权的巨磁热La(Fe0.92Co0.08)11.9Si1.1材料体系获得静水压大幅增强的磁热和压热效应，结合中子衍射和第一性原理计算从原子尺度揭示了相关机理。（Chem.Mater. 2020:32, 1807-1818）.4.在FeRh/PMN-PT体系实现了电场对磁热综合性能和相变温区的动态调控。在此基础上设计了电场磁场双场激励的AMR循环。（Acta Mater. 2020:191, 51-59）.5.在Mn0.87Fe0.13NiGe体系发现一种新的自旋结构，并获得了巨大负热膨胀和压磁效应。（J.Am.Chem.Soc. 2021, 143: 6798-6804）.6.澄清了长期争议的具有负热膨胀性质的巨磁热材料自旋熵变和晶格熵变的符号问题。（中国科学, 2021,51: 067520）..相关成果在J.Am.Chem.Soc.、Nano Energy 、Mater.Horiz. 、NPG Asia Mater.、Acta Mater. 、Script Mater.、ACS AMI、Appl.Phys.Lett.等刊物发表论文33篇，获授权发明专利5项(其中国际专利授权2项)，提交发明专利申请5项。国内、国际邀请报告20余次。举办学术会议2次。培养博士、硕士研究生15名，毕业博士生9名。