铁磁性元素掺杂CaB6单晶体的制备及性能表征

In this project, a series of structural models of the alkaline-earth metal boride crystals with magnetic semiconductor property will be designed by first principles calculations. The forming possibility of these crystals under high pressure and their physical properties will be also predicted. We will explore the forming process of large alkaline-earth metal (Ca, Sr) borides crystals doped by transition metal Mn and magnetic Fe, Co, Ni using a special liquid-solid reaction between the metal and B under high pressure in combination with the structure analyses technic. Some new alkaline-earth metal boride magnetic semiconductors with larger size will be synthesized. The essential physical properties for these magnetic semiconductors will be measured in a temperature range of 2-1000K by a physical property measurement system (PPMS), thermal constants measuring apparatus (TC-7000H) and Seebeck coefficient measuring apparatus (ZET-2). We will elucidate the relation between the physical properties and the crystal structure, chemical bond state and electronic distribution to investigate forming mechanism of ferromagnetism and semiconductor properties found in these magnetic semiconductors. Basing on the research results obtained in this project, we should be able to synthesize several new metal borides with outstanding magnetic semiconductor property, which is a basic so as to further understand the formation and physical property of quantum spin state crystal materials, and exploit them in spintronic devices.

本项目将采用第一性原理的计算方法，设计出系列的碱土金属硼化物基磁性半导体结构模型，预测其高压下形成的可能性和基本物理性质；通过高温高压液固反应合成技术，结合物相结构分析手段，从实验上探索过渡金属Mn和磁性金属Fe、Co、Ni掺杂碱土金属硼化物单晶体的形成规律，合成出系列新型碱土金属(Ca、Sr)硼化物磁性半导体大尺寸单晶材料；采用物理性能测试系统(PPMS)和高温热导仪(TC-9000H)及Seeback系数测定仪等现代测试分析手段，研究所制备磁性半导体单晶体在2-1000K温度范围内的基本物理性质，阐明物理性质与晶体结构、价键结构和电子结构的关系，探索铁磁性元素掺杂碱土金属硼化物单晶体磁性和半导体性的形成机理。本项目开展的研究工作将在实验上制备系列具有优异磁性半导体性能的碱土金属硼化物晶体材料，为深入理解自旋电子材料的形成规律和物理性能以及自旋电子学器件的开发应用奠定研究基础。

采用基于第一性原理开发的材料预测软件CALYPSO、MS、VASP和Wien2k等，构建了多种碱金属、碱土金属和过度金属硼化物等多种新结构，并对其晶体结构、能带结构、声子振动特性、费米面附近电子自旋态和高压形成规律等基本物理性质进行了广泛探索。应用六面顶大腔体合成技术成功合成了多种Mn掺杂Ca-B体系和碱金属硼碳体系化合物毫米级单晶材料，应用物理性能测试系统（PPMS）等技术，对所获得的单晶材料的基础电学性能和磁阻效应及霍尔效应等磁学性能等进行了系统研究，基本阐明了物理性能与价键结构的关系；但对Mn掺杂Ca-B体系的磁学方面出现的新现象形成机制还需要进一步深入分析。由于疫情的影响，导致研究组所购置的大型超高压合成系统调试延期，因此，合成的单晶材料尺寸仅达到毫米级。我们已经掌握了高温高压条件下大尺寸金属硼化物单晶的制备技术，预期在未来的两年内可获得厘米级多种金属硼化物单晶材料，届时可获得(Ca1-xMx)B6（x=0.005~0.05）单晶材料磁性半导体性能的详细研究结果，为后续的应用开发奠定基础。

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