特殊功能Heusler合金的电子结构和基本物性的研究

发布时间：2018-08-12 10:11

【摘要】：Heusler合金蕴含着丰富的物理现象和应用功能,已经成为开发新型功能材料的巨大资源宝库,并在磁机、磁电、磁热等领域展现出巨大的开发和应用潜力。本论文主要工作是探索和合成具有新的功能特性的Heusler合金,深入研究它们的物理性质以及所具有的功能特性。主要成果概括如下:报道了一种新型具有晶格对称性不变相变的铁磁性形状记忆合金:半Heusler结构的CoMnGa合金。该合金在发生一级相变时,晶格对称性保持不变,而体积和磁结构发生巨大变化。Co-Mn反占位能够调控相变驱动力和相变势垒,我们通过严格的退火和淬火工艺调控了Co-Mn反占位的含量,从而成功的诱导了伴随有铁磁-亚铁磁转变的晶格对称性不变相变。通过第一性原理计算,研究了Co2TiSb1-x Snx(x=0,0.25,0.5)系列合金发生马氏体相变的可能性。通过甩带快淬的方法合成了具有L21结构的Co2TiSb1-x Snx(x=0.25,0.5)合金。并从实验上观察到了Co2TiSb0.75Sn0.25合金中的马氏体相变行为。通过理论计算,预测含有Co-Mn反占位的CoVMnAl合金是一种完全补偿的亚铁磁性半金属材料。制备出了具有30%Co-Mn反占位的CoVMnAl合金,磁性和输运性质的测量结果证实了材料的半金属性和完全补偿的亚铁磁性。CoVMnAl合金的半金属性和亚铁磁性来源于材料中的原子反占位,该方法克服了传统的反占位缺陷破坏半金属性的问题,基于原子间的反占位缺陷诱导出半金属性和亚铁磁性的方法将开发出更多新的半金属材料。通过用Fe原子连续替换CoTiSb基体中的Ti,Ti-Sb或Co原子的方法,设计出了一种具有100%自旋极化率的Fe基单原子链。发现Fe-Sb和Fe-V(空位)原子链表现出100%的自旋极化率,形成了一个极小的单自旋通道,而Fe-Fe原子链表现出自旋无能隙半导体的性质。开发出一种特殊的自旋无能隙半导体材料:Mn2.25Co0.75Ga0.5Sn0.5合金。材料具有高有序的原子排列方式、2μB的饱和磁化强度和高达720K的居里温度。Mn2.25Co0.75Ga0.5Sn0.5合金具有高于反常霍尔效应两个数量级的巨大的正常霍尔效应,该现象从未在其它磁性或非磁性材料中报道过。随着磁场强度的增加,巨大的正常霍尔效应造成总霍尔电压由负转变为正。7K下材料的反常霍尔电导率为13.7S/cm,且此时表现为正线性磁阻。随着温度升高,材料表现出由正到负的双重交叉磁阻现象,而该现象则是自旋无能隙半导体材料的典型特征。
[Abstract]:Heusler alloys, which contain abundant physical phenomena and application functions, have become a great resource for the development of new functional materials, and have shown great potential for development and application in the fields of magnetic machine, magnetoelectricity, magnetocalorimetry and so on. The main work of this thesis is to explore and synthesize Heusler alloys with new functional properties, and to study their physical properties and functional properties. The main results are summarized as follows: a new ferromagnetic shape memory alloy with lattice symmetry invariant phase transformation: CoMnGa alloy with semi-Heusler structure is reported. When the first order phase transition occurs, the lattice symmetry remains constant, while the volume and magnetic structure change greatly. The inverse position of Co-Mn can regulate the driving force and barrier of phase transition. Through strict annealing and quenching processes, we control the content of Co-Mn inverse sites, thus successfully inducing the lattice symmetry invariant phase transition accompanied by ferromagnetic and ferromagnetic transition. The possibility of martensitic transformation in Co2TiSb1-x Snx (x0. 0. 25 ~ 0. 5) alloys has been studied by first principle calculation. Co2TiSb1-x Snx alloy with L 21 structure was synthesized by rapid quenching. The martensitic transformation behavior in Co2TiSb0.75Sn0.25 alloy was observed experimentally. By theoretical calculation, it is predicted that the CoVMnAl alloy with Co-Mn antioccupation is a fully compensated ferromagnetic semi-metallic material. The magnetic and transport properties of CoVMnAl alloy with 30%Co-Mn antioccupation have been prepared. The semi-metallic properties of the material and the fully compensated ferromagnetism. CoVMnAl alloy have semi-metallic properties and ferromagnetism derived from the atomic antioccupation in the material. This method overcomes the problem that anti-occupying defects destroy the semi-metallic properties. The method of inducting semi-metallic and ferromagnetic properties based on interatomic antioccupation defects will develop more new semi-metallic materials. A Fe-based monoatomic chain with 100% spin-polarizability was designed by replacing Ti-Ti-Sb or Co atoms in CoTiSb matrix continuously with Fe atoms. It is found that the spin polarizability of Fe-Sb and Fe-V atom chains is 100%, and a single spin channel is formed, while the Fe-Fe atomic chain exhibits the properties of self spin energy gap semiconductor. A special spin-free semiconductor material, W mn 2.25Co 0.75Ga 0.5Sn0.5, has been developed. The material has a highly ordered atomic arrangement of 2 渭 B saturation magnetization and a Curie temperature of 720K. Mn2.25Co0.75Ga0.5Sn0.5 alloy has a large normal Hall effect of two orders of magnitude higher than the anomalous Hall effect. This phenomenon has never been reported in other magnetic or nonmagnetic materials. With the increase of magnetic field intensity, the anomalous Hall conductivity of the material changes from negative to positive. 7K due to the large normal Hall effect, and the anomalous Hall conductivity is 13.7s / cm, and it shows positive linear magnetoresistance. With the increase of temperature, the material exhibits a double cross magnetoresistive phenomenon from positive to negative, which is a typical feature of spin-gap semiconductor materials.
【学位授予单位】：河北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG139.6

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