自旋序诱导的多铁性氧化物单晶磁热效应的研究与调控

Magnetic refrigeration technology based on the magnetocaloric effect (MCE) has received much attention due to its energy-efficient and environment-friendly features. For years, magnetic refrigeration materials, as a key part of the technology, have been hotly investigated in the field of the condensed matter physics and material science. The richness of the MCE and the prospects for practical application involved in multiferroic materials are currently attracting considerable interest from both experimental and theoretical point of view. The project aims at the MCE of the multiferroic transition metal materials DyFeO3、GdFeO3 and CuFeO2. The high-quality single crystals are grown by using a floating-zone technique; the quality of the crystals is carefully checked by using the x-ray diffraction and Laue photograph, and simultaneously cut precisely along the crystallographic axes; the fundamental physical properties of these crystals are characterized by the magnetization and specific heat measurements under different magnetic fields and temperatures. Combining the theoretical calculations, the magnetic properties、 magnetocaloric properties and magnetic refrigerant capacity under different magnetic field are detailedly analyzed. Then it is attempted to clarify the physical mechanism of the MCE and whether these materials could be considered as candidates for magnetic refrigerant at low temperatures. In addition, the MCE of these materials with partial substitution of elements will be further investigated. It can provide basic insights on improving performance in magnetic refrigeration efficiency with large magnetic entropy change and high magnetic refrigerant capacity over the existing multiferroic materials, and it is also very helpful for the deeply understanding of the fundamental physical origin of the MCE of these multiferroic materials.

基于磁热效应的磁制冷技术因其高效节能以及环保等优点而备受关注，作为该技术关键的磁制冷材料一直以来都是凝聚态物理和材料科学研究的热点。近年来多铁性材料磁热效应的研究成为实验和理论工作中新的亮点。本项目针对多铁性过渡金属氧化物 DyFeO3、GdFeO3以及CuFeO2 的磁热效应展开研究。利用光学浮区法制备高品质的单晶样品，利用 X 射线衍射以及 Laue 照相等技术对单晶样品进行质量的表征和精确的定向；利用磁学以及比热测量系统对样品在不同磁场和温度下的物性做细致地测量。结合理论计算，研究不同磁场下体系的磁性、磁熵变以及磁制冷能力；弄清影响磁热效应的物理机制，分析体系是否具备成为低温磁制冷材料的潜力。进一步通过元素掺杂或替代对多铁性过渡金属氧化物磁热效应的性能进行调控，探索具有更高磁熵变以及更强磁制冷能力的多铁性材料，深入对影响体系磁热效应的微观物理机制的理解，为探索新型磁制冷材料提供思路。

本项目针对多铁性过渡金属氧化物 DyFeO3、GdFeO3以及ErMnO3 的磁热效应展开研究。利用光学浮区法制备高品质的单晶样品，利用 X 射线衍射以及 Laue 照相等技术对单晶样品进行质量的表征和精确的定向；利用磁学以及比热测量系统对样品在不同磁场和温度下的物性做细致地测量。结合理论计算，研究不同磁场下体系的磁性、磁熵变以及磁制冷能力；进一步通过元素掺杂或替代对多铁性过渡金属氧化物磁热效应的性能进行调控，弄清影响磁热效应的物理机制。此外，通过传统的固相反应法制备了TbFeO3和Na0.5Bi0.5Cu3Ti4O12陶瓷样品。利用温谱，阻抗谱和模量谱等手段对陶瓷样品进行了介电性能研究。我们发现了大量的介电弛豫过程，并分析得出产生介电响应的物理机制。我们还报道了GaAs单晶中的巨介电行为，该行为与传统的氧化物材料所表现出的巨介电行为有所不同，因此可以将GaAs单晶中介电行为视为一类新型的巨介电行为。