稀土掺杂AT2X2型层状结构材料中的磁性、结构及其关联性研究

Structure is the major factor affecting the nature of material, the change of structure will lead to different physical properties. The discovery of 122-type iron-based superconductors (FeSCs) has attracted people's interest in investigating AT2X2 materials. In addition to superconductivity, magnetism becomes the most studied object in this type of material, and whose studies is mainly focused on ACo2Pn2 system. There have some theoretical and experimental results in ACo2P2 system to investigate the effect of structure on magnetism, while there still have no systematical understanding about their relationship. Besides, compared with ACo2P2, more experimental investigation are needed in the ACo2As2 system.. In this project, we will choose CaCo2As2 as our targeted material. Through tuning the structure and physical properties with rare-earth doping, we can investigate the correlation between magnetism and structure. We plan to introduce different rare-earth element doping into CaCo2As2 and study the influence of temperature, magnetic field, doping on the crystal structure, magnetism and electronic structure, respectively. Then we can obtain the magnetic phase diagram, analysis and establish the basic physical image about the relationship between structure and magnetism in CaCo2As2 system. Besides, by comparing with FeSCs, the results in this project could provide some experimental evidence or clues in understanding the reason why only iron-based compounds exist high-temperature superconductivity among AT2X2 material.

材料结构是影响其性质的主要因素，结构的变化会导致出现不同的物理性质。122体系铁基超导体的发现吸引了人们对AT2X2型材料的研究，其中有关磁性的研究成为了除超导电性外最备受关注的对象。磁性的研究主要集中于钴磷族化合物ACo2Pn2，现已有一系列工作研究了ACo2P2中结构对磁性的影响，但还没有形成系统的认识；同时,相对于ACo2P2中众多的研究成果，ACo2As2体系还需进一步的实验研究。本项目将以层状结构的CaCo2As2为对象，用稀土掺杂的方法来调控体系的结构与物性，研究其磁性与结构的关联作用。我们将制备不同体系掺杂的CaCo2As2样品，研究温度、磁场、掺杂对体系晶格结构、磁性、电子结构等影响的异同，得到磁性随掺杂变化的相图，并建立起三者之间关联的基本图像。本项目成果也将与铁基超导相关结果进行比较，为理解AT2X2材料中只有铁基化合物具有高温超导电性的原因提供一定的实验证据与线索。

材料的结构与其物理性质息息相关，具有AT2X2层状结构的122体系铁基超导的发现吸引了人们对具有同类结构材料的研究兴趣，其中磁性成为了除超导电性外最备受关注的对象。CaCo2As2由于具有坍塌的四方相结构，具有和其他ACo2As2(A=Sr，Ba)完全不同的磁性质。本项目以CaCo2As2为主要对象，通过引入稀土掺杂的方式来调控其物理性质，研究了掺杂、温度、磁场等对其结构与磁性的影响机理，主要研究内容包括：.(1)利用助溶剂法制备了稀土Pr，La，Sm掺杂的Ca1-xRxCo2As2高质量单晶；(2)发现Pr的引入会使得CaCo2As2由A型反铁磁态转变为铁磁态，且随着Pr掺杂浓度的增加，体系出现Co3d与Pr4f电子自旋的反铁磁耦合作用，最终还给出了Ca1-xPrxCo2As2掺杂依赖的磁相图；(3)在Ca1-xLaxCo2As2中发现Co的3d电子自旋由于稀土La的引入也转变为铁磁有序，且该体系的结构和铁磁居里点与La掺杂浓度之间存在明显的正相关关系；(4)不同于Pr/La掺杂体系，在Ca1-xSmxCo2As2中我们发现Co的3d电子自旋并未表现出磁有序态，其铁磁有序主要来自于Sm4f电子自旋的贡献，同时Sm掺杂使得体系的易磁化方向由最初的面外变成了面内。本项目的开展在揭示稀土掺杂Ca1-xRxCo2As2体系的结构、磁性及其关联性机理的同时，也将为铁基超导及相关磁性材料物性调控的研究提供实验和理论参考。