在铁基超导体被发现之前，磁性一直以来被认为对超导电性起到抑制作用，由强磁性 离子组成的铁基超导体系的出现则打破了人们这一传统的认知。在铁基超导体中，超导电 性是随着静态反铁磁序的被压制而逐渐显现，一些体系的相图中反铁磁相与超导相之间还 存在相互交叠的区域，并且在这一区域内观测到了两者之间存在着某种竞争/共存相互关 系的实验证据，自旋涨落也普遍被视为声子的替代而成为超导电子的配对胶。其相图中另 一重大发现则是在施加单轴压力退孪晶的铁基材料中观测到了电子向列相，其与体系的 磁序、轨道和晶格之间均表现出一定的关联，并且很有可能对超导电性也存在一定的影 响。在不同体系的非常规超导体内人们还都观测到了与高温超导电性相紧密关联的集体 激发——中子自旋共振峰，目前对其微观起源的探究也是研究热点之一。通过探究铁基 超导体内其它有序相对中子自旋共振峰的作用，我们可以很好地了解其微观特性，并进 一步理解高温超导电性的本质。在本文工作中，我们选用了具有代表性的“122”体系电 子型欠掺杂样品，Ba(Fe1−xCox)2As2（x=0.048 和 0.054），其在相图中位于反铁磁相与超导 电相相互交叠的区域，此前在对其输运测量和能带测量过程中均观测到了与体系向列相 相关联的各向异性，因此该样品可以很好的满足我们探究中子自旋共振峰和向列相之间 联系的目的。此外，我们还选用存在较强向列极化率的欠掺杂组分样品（x=0.026），探究 了施加面内单轴压力对材料的磁有序结构的影响。我们还进一步对具有简单晶格结构的 “11”体系铁硫族化合物的相图进行探究，目前对位于 Fe1+yTe1−xSex 体系相图中超导相和 反铁磁相之间过渡区域内的磁性本质还存在着一些争论，我们则选用位于这一掺杂区间的 Fe1.07Te0.8Se0.2 样品探究其短程磁序的本质。

本文的研究内容及结果主要包含以下几个部分：

• 我们利用非弹性中子散射技术对施加单轴应力退孪晶的 Ba(Fe1−xCox)2As2（x=0.048 和 0.054）单晶样品进行测量。我们通过分析位于面内具有四重旋转对称性的（1,0）和 （0,1）位置处的低能自旋激发，我们发现其表现出的各向异性随着温度的升高而逐渐减 弱，并且各向异性可以持续到温度 T≫TS。这一现象与前人在该体系中所观测到的沿 a、 b 方向电阻率之间的差异随温度的变化以及轨道序中不同电子轨道间能量差随温度变化 趋势基本相同。 

• 在 Ba(Fe1−xCox)2As2（x=0.048 和 0.054）材料中，我们在体系低能磁谱位置处观测到清 晰的中子自旋共振峰，并且其信号只出现在面内的（1,0）位置，此位置则对应为费米面 上的 dyz 轨道沿 Γ-X 方向的嵌套波矢。由此我们可以得到在该体系中中子自旋共振峰表 现出明显的轨道选择特性，并只源自于 dyz 轨道电子的贡献。 • 通过分析上述材料的低能能谱特点，我们可以得到体系中的向列相以及其在轨道自由度 上所表现出的轨道序会对体系的费米面结构及形状进行调整，进而调节费米面的嵌套条 件，这就导致体系在进入向列相后表现出自旋激发各向异性以及中子自旋共振峰的轨道 选择特性。

• 我们利用极化中子散射技术对施加单轴应力的 Ba(Fe0.974Co0.026)2As2 单晶样品进行测量 （∆T = TS -TN≈10K）。通过分析在自旋翻转模式下沿自旋三个极化方向的磁散射信号对 温度和能量依赖关系，我们发现当体系经过 TN 时，除了沿 a 轴方向的磁涨落 Ma 会发 生发散现象外，沿 c 轴的 Mc 也会发生发散，这与在 BaFe2As2 中观测到的现象相一致， 这表明单轴压力诱导材料磁序易轴发生偏转的现象在铁基超导体中是较为广泛存在的。

• Ba(Fe0.974Co0.026)2As2 材料的极化中子散射实验结果还表明，在温度降低至 T* 以下，低 能磁激发信号强度在自旋的三个极化方向存在明显的区别；而在 TN 以下，三个方向的 自旋能隙大小也是存在明显差异的。这些磁各向异性特征表明了自旋轨道耦合在铁基超 导材料中的重要性。

• 我们利用输运测量方法对 Fe1.07Te0.8Se0.2 材料的直流磁化率和交流磁化率实部随温度和 直流场的变化关系进行了测量，此外还利用中子衍射技术测量了材料在其非公度磁波矢 位置处的磁性序参量随温度的变化趋势，以及该趋势对谱仪能量分辨率的响应，得到了 材料中短程磁序的本质实为自旋玻璃态的坚实证据。

• 通过对 Fe1.07Te0.8Se0.2 材料在 O2 气氛中进行退火处理而得到 FeTe0.8Se0.2 材料，测量两者的磁矩随温度的变化关系我们得到材料中过量的 Fe 对体系的超导电性起到抑制作用， 并且其与面内 Fe 之间的磁相互作用可能是形成自旋玻璃态的原因。

Before the discovery of the iron-based superconductors, the magnetism was usually treated as detrimental to the superconductivity, the emergence of the iron-based superconductors composed of the strong magnetic iron ions breaks the people's traditional perspective as above. In the Iron-based superconductors, the superconductivity emerges gradually as the static antiferromagnetic order is suppressed, furthermore, people found there is a overlapped area in the phase diagrams of the iron-based superconductors between the antiferromagnetic and superconducting phases and observed experimental phenomena about some certain competing or coexist interactions there, the spin excitation is also commonly seen as a substitute for the phonon as the pairing glue for the superconducting electrons. Another significant discovery in the phase diagrams of the iron-based superconductors is the discovery of the electronic nematic phase, it is correlated to the magnetic order, orbit, and lattice of the system and could likely affect the superconductivity. A collective excitation, the neutron spin resonance, which is found to be closely correlated with the high-temperature superconductivity, has also been observed in different systems of unconventional superconductors, the research on its microcosmic origin is also one of the hot topics at present. By exploring the interactions between other ordered phases and the neutron spin resonance in the iron-based superconductors, we can have a clear understanding of the spin resonance's microscopic characteristics and a more particular knowledge of the nature of the high-TC superconductivity. In the work of this thesis, we chose the representative electron underdoped samples in the "122" system in the iron-based superconductors, Ba(Fe1−xCox)2As2 (=0.048 and 0.054), they locate at the overlapped area between the antiferromagnetic and superconducting phases in the phase diagrams, the anisotropy associated with the nematic phase of the system was previously reported in the transport and energy band measurements, therefore, these samples can well meet our purpose of exploring the relationship between the neutron spin resonance and the nematic phase. In addition, we chose the electron underdoped samples (x=0.026), which have relatively strong nematic susceptibility, to explore the influence of the uniaxial pressure on their magnetic order.We also explored the phase diagrams of the "11" system of the iron chalcogenides, which equipped with a more simple lattice structure, there still have been some controversies about the nature of the magnetic order in the transition region between the superconducting and the antiferromagnetic phases in the phase diagram of the Fe1+yTe1−xSex system, we chose the Fe1.07Te0.8Se0.2 samples, which locate in this doping interval, to explore the nature of the short-range magnetic order in this system.

The research contents and results of this thesis mainly include the following parts:

• We measured the detwinned Ba(Fe1−xCox)2As2 (x=0.048 and 0.054) single crystals applied with uniaxial pressure by the inelastic neutron scattering method. Through analyzing the spin excitation with low energy at the in-plane tetragonal symmetric positions (1,0) and (0,1), we found that the anisotropy between them gradually vanishes with the increasing temperature, and it can persist at the temperature T ≫ TS . This phenomenon is consistent with the previous observations in this system, including the temperature dependence of the difference in resistivity along with a and b directions and the energy difference between different electron orbitals in the orbital order.

• We observed the clear neutron spin resonance signal at the low energy magnetic spectrum of the system and the signal only emerges at the in-plane (1,0) position, which corresponds to the nesting vector of the dyz orbital at the Fermi surface along the Γ——X direction. Therefore, we conclude that the spin resonance in this system shows clear orbital selective characteristic and only contributed by the electrons in the dyz orbital.

• Through the analysis of the low energy spectrum characteristics of the samples mentioned above, we can deduce that the nematic phase and the orbital order which is the representation of the nematic in the degree of orbital freedom, will adjust the Fermi surface structure and the shape of it, the nesting condition will be further adjusted too, these result in the orbital selectivity of the spin resonance and the anisotropy of the spin excitation when the system enters into the nematic phase.

• We measured the Ba(Fe0.974Co0.026)2As2 applied with the uniaxial pressure by the polarized neutron scattering method (∆T = TS -TN≈10K). Through analyzing the temperature and energy dependence of the scattering intensity of the three spin polarized directions in spin flip mode, we found that when the system goes through TN, not only the Ma, which is the magnetic fluctuation along the a axis, will diverge, the Mc, which is along c axis, will do too, this phenomenon is coincide with the discovery in BaFe2As2, which means the phenomenon of the tilting of the magnetic easy axis induced by the in-plane uniaxial pressure is relatively common in iron-based superconductors.

• The results of the polarized neutron scattering experiments on Ba(Fe0.974Co0.026)2As2 also show that, the scattering intensities of low energy magnetic excitation in three spin polarized directions exhibit obvious differences when cooling down below T*; when cooling further below TN, the spin gaps in three directions are also different. These magnetic anisotropy phenomena show the importance of spin-orbital coupling in iron-based superconductors.

• We measured the temperature and the magnitude of the DC field dependence of the DC magnetic susceptibility and the real part of the AC magnetic susceptibility of Fe1.07Te0.8Se0.2 by transport measurements, moreover, we measured the temperature dependence of the magnetic order parameter at the incommensurate magnetic wave vector and its response to the instrument resolution by the neutron diffraction method. The solid evidences are obtained through the results above that the magnetic nature of the material is actually a spin glass state.

• By annealing Fe1.07Te0.8Se0.2 in O2 atmosphere, FeTe0.8Se0.2 sample was obtained. We measured the temperature dependence of the magnetic moments in both the annealed and unannealed samples and found that the excess Fe in the crystals is detrimental to the superconductivity, furthermore, the magnetic interaction between the excess Fe and the one in the Fe-Fe plane might account for the origin of the spin glass state in the system.