如何突破传统电子器件的局限，设计出性能更稳定、功耗更低、读写速度更快和度更高的器件是当前的研究热点。自旋电子器件将电子的自旋自由度考虑进来，为微电子技术带来了新的活力。然而，为了使自旋电子器件满足日益增长的行业需求，需要探索性能更优的材料。反铁磁材料因其本征频率高、无杂散场和抗外磁场干扰等特点，吸引了研究人员的广泛关注。磁化动力学中的阻尼特性反映了磁性能的耗散，是提高自旋电子学器件性能的关键。理论分析可以为器件性能的优化提供有参考价值的依据，所以，我们在第一性原理计算的框架下，对反铁磁材料中的磁化动力学行为和相关的输运现象进行了研究。本文的主要内容由以下三个方面组成：
借助于第一性原理输运计算，我们对块体反铁磁材料中的阻尼效应和输运现象进行了研究。首先，我们将铁磁耗散散射理论推广到反铁磁体系中，得到了反铁磁体系中和磁化动力学过程相关的耗散散射理论。然后，我们系统地计算了反铁磁材料铂锰(PtMn)，铱锰(IrMn)，钯锰(PdMn)和铁锰(FeMn)中的阻尼系数，并对其中的物理机制进行了讨论。随后，我们将温度效应考虑进来，讨论了温度对反铁磁材料中阻尼系数和各项异性磁电阻的影响。最后，以双子格子反铁磁共振为例，说明了真实的阻尼系数对反铁磁共振线宽的影响。
通过将理论计算与实验测量结果相结合，我们进一步研究了反铁磁厚度对铁磁|反铁磁异质结中阻尼系数的影响。实验测量发现，随着反铁磁厚度的增加，异质结中的阻尼呈现出先增大后减小的趋势，异于通常对于铁磁|反铁磁异质结中阻尼系数的认识。通过第一性原理输运计算，我们系统地研究了不同反铁磁相对铁磁|反铁磁异质结中阻尼系数的影响，说明了实验中的异常行为源自界面处的交换偏置效应。交换偏置场的存在促使反铁磁跟随铁磁材料发生受迫进动，受迫进动会向铁磁层泵浦出自旋流，降低由于铁磁泵浦对阻尼带来的影响，从而得到上述异常的行为。
通过第一性原理计算，我们研究了补偿反铁磁衬底锂锰氧化物(Li2MnO3)对磁近邻耦合单层二硒化钨(WSe2) 中输运性质和自旋极化现象的影响。结果显示，由于晶格不匹配，补偿反铁磁界面可以破坏WSe2中的时间反演对称性，导致WSe2中具有剩余的净磁矩，进而可在WSe2的价带观察到自旋极化。将计算结果与低能有效哈密顿量模型所得到的结果进行对比，确定了自旋极化是由WSe2中谷简并度的破缺所致，并指出补偿反铁磁界面也能为WSe2供较大的有效磁场。进一步，通过引入应力，发现自旋极化可以被应力很好地调控。通过瓦尼尔函数方法，我们发现可在WSe中探测到自旋极化的反常霍尔效应，同时，也可观测到Li2MnO3贡献的晶体霍尔效应。

How to break through the limitations of traditional electronic devices and design devices with more stable performance, lower power consumption, faster read and write speed and higher density is a hot topic in the current research. Spintronic devices take into account the spin freedom of electrons, bringing new vitality to microelectronics technology. However, in order to enable spintronics to meet the growing needs of industry, we need to explore better performing materials. Antiferromagnetic materials have attracted wide attention from researchers because of their high intrinsic frequency, absence of stray fields, and resistance to external magnetic field interference. The damping characteristics in magnetization dynamics reflect the dissipation of magnetic energy and are key to improving the performance of spintronics devices. Theoretical analysis can provide a valuable basis for the optimization of device performance. So, within the framework of first-principles calculations, we study the magnetization dynamic behavior and related transport phenomena in antiferromagnetic materials. The main content of this thesis consists of the following three aspects:
Using first-principles transport calculations, we studied the damping effects and transport phenomena in antiferromagnetic materials. First of all, we generalize the ferromagnetic dissipative scattering theory to the antiferromagnetic system, and obtain the dissipative scattering theory related to the antiferromagnetic magnetization dynamics. We then systematically calculated the damping coefficient in the antiferromagnetic material PtMn, PdMn， IrMn and FeMn and discussed the physical mechanisms in it. Subsequently, we consider the temperature effect and discuss the effect of temperature on the damping coefficient and anisotropic magnetoresistance in antiferromagnetic materials. Finally, taking the antiferromagnetic resonance as an example, the effect of the real damping coefficient on the antiferromagnetic resonance linewidth is illustrated.
By combining theoretical calculations with experimental measurements, we further investigate the effect of antiferromagnetic thickness on the damping coefficient in ferromagnetic|antiferromagnetic heterostructure. The experimental measurements show that with the increase of the antiferromagnetic thickness, the damping in the heterostructure shows a trend of first increasing and then decreasing, which is different from the usual understanding of the damping coefficient in the ferromagnetic|antiferromagnetic heterostructure. Through first-principles transport calculations, we systematically investigate the influence of different antiferromagnets phase on the damping coefficients in the heterostructure, and show that the abnormal behavior in the experiment is due to the exchange bias effect at the interface. The existence of the exchange bias field causes the antiferromagnetism to follow the ferromagnetic material to undergo forced precession, and the forced precession will pump the spin current to the ferromagnetic layer, reducing the influence of the ferromagnetic pumping on the damping, thereby got the above abnormal behavior.
Through first-principles calculations, we investigate the effects of the compensated antiferromagnetic substrate Li2MnO3 on the transport properties and spin-polarization phenomena in monolayer WSe2. The results show that due to lattice mismatch, compensated antiferromagnetic interface can break the time-reversal symmetry in WSe2, resulting in a residual net magnetic moment in WSe2, which in turn can observe spin polarization in the valence band of WSe2. By comparing the results with those obtained from the effective low energy Hamiltonian model, it is confirmed that the spin polarization is caused by the breaking of the valley degeneracy in WSe2, and it is pointed out that the compensated antiferromagnetic interface can also provides a large effective magnetic field for the WSe2. Furthermore, by introducing stress, it is found that the spin polarization can be well tuned. By means of the Wannier function method, we find that the spin-polarized anomalous Hall effect can be detected in WSe2. At the same time, the crystalline Hall effect contributed by Li2MnO3 can also be observed.