稀土-过渡族化合物磁热效应的物理机理研究

The refrigeration technique based on the magnetocaloric effect (MCE) of magnetic materials has prominent advantages over the conventional technique in the sense of its high efficiency and friendly environment. The study on the relative physics problems of magnetocaloric effect will has an important meaning for exploring novel magnetic refrigeration materials with large magnetocaloric effect. In this project, we will investigate the effect of phase transition process induced by multifield (magnetic field, pressure, temperature) on magnetocaloric effect in first-order magnetic transition systems, such as La(Fe,Si)13-based compounds, the rule of change in lattice entropy change induced by multifield, the physics origin of thermal/magnetic hysteresis, the effective way of obtaining large magnetocaloric effect in rare-earth intermetallic compounds. Through our effort in this project, we will (1) understand the influencing mechanisms of phase transition, magnetization process, itinerant electron metamagnetic transition controlled by multifield on magnetocaloric effect in materials with first-order magnetic transition, (2) understand the different contributions of magnetic entropy change, lattice entropy change and electronic entropy change in different magnetocaloric systems, obtain the effective means for changing lattice entropy change and avhieve the increase of total entropy change, (3) understand the machanism of hysteresis loss, obtain the effective means of reducing hysteresis and effectively increase refrigeration capacity in magnetocaloric materials, and (4) understand the relations between the crystal structure, magnetic structure, magnetic phase transition and magnetocaloric effect in rare-earth intermetallic compounds, synthesize novel magnetocaloric materials with large magnetocaloric effect.

基于磁热效应的磁制冷技术具有广阔的应用前景，深入研究磁热效应的物理机理，对探索大磁热效应的新型磁制冷材料具有重要意义。本项目拟重点研究具有大磁热效应的一级相变体系（例如LaFeSi）在多场诱导下影响相变过程、相变性质的物理因素及其对磁热效应的影响，多场调控下晶格熵变的变化规律，一级相变体系中出现热滞/磁滞的现象及原因，以及探索获得稀土金属间化合物大磁热效应的有效途径。通过本项研究1）清楚多场作用下一级相变材料中相变过程和相变性质以及交换作用、磁化过程、变磁转变等对磁热效应的影响机制；2）清楚不同体系中磁熵变、晶格熵变、电子熵变的贡献，获得改变晶格熵变的方法，实现体系总熵变的共振增强；3）清楚一级相变体系中产生磁滞、热滞的因素，获得克服和抑制材料磁滞、热滞的方法，有效提高磁热效应材料的制冷能力；4）清楚稀土金属间化合物的晶体结构、磁结构、磁相变与磁热效应的关系，合成出新型高性能磁热效应材料。

与普通的气体制冷相比，基于磁热效应的磁制冷技术具有高效节能和绿色环保的优点，越来越受到国内外研究者的重视，新型磁制冷材料的探索和磁热效应的研究一直是国际上研究的热点课题。在具有一级相变的磁热效应材料中，LaFeSi系列是国际上普遍认为具有重要应用前景的磁制冷工质之一，也是我国具有自主知识产权的材料。本项目系统研究了间隙原子C和H对LaFeSi和LaFeAl稀土化合物磁性和磁热效应的影响，进一步清楚了一级相变材料中在多场诱导下影响相变过程、相变性质的物理因素及其与磁热效应的关系，清楚了一级相变体系中产生磁滞、热滞的因素和获得克服和抑制材料磁滞、热滞的方法，有效提高了磁热效应材料的制冷能力，通过工艺改进研制出了实用性粘接LaFe基高性能磁制冷材料。我们还系统研究了具有低温相变的二元稀土基金属间化合物(RGa，RSi，R12Co7，RMn2等)和稀土-过渡金属-主族金属三元化合物(RTSi，RTAl，RT2Si2，R2CoGa3等，其中R代表稀土元素, T 代表过渡金属)的磁性和磁热效应，弄清楚了稀土金属间化合物的晶体结构、磁结构、磁相变与磁热效应的关系，以及不同体系中磁熵变、晶格熵变、电子熵变对磁热效应的贡献，还合成出了多种新型低温相变高性能磁热效应材料，可望在液氦、液氢、液氮以及天然气制冷等方面获得应用。本项目共发表学术文章52篇，其中SCI文章50篇，获国家发明专利授权12项，申请国家发明专利3项。组织全国磁热效应和磁制冷技术学术会议2次，参加国内外学术会议10次以上。毕业博士研究生3名，在读博士研究生1名。获2014年度陈嘉庚技术科学奖。