Antiferromagnets are promising candidates as active components in spintronic applications. They share features with ferrimagnets in that opposing spin orientations exist in two or more sublattices. Spin transfer torque and spin pumping are essential ingredients in antiferromagnetic and ferrimagnet spintronics. This paper develops an out-of-equilibrium quantum theory of the spin dynamics of collinear magnets containing many spins coupled to normal metal reservoirs. At equilibrium, the spins are parallel or antiparallel to the easy axis. The theory, therefore, covers collinear antiferromagnets and ferrimagnets. We focus on the resulting semi-classical spin dynamics. The dissipation in the spin dynamics is enhanced due to spin-pumping. Spin accumulations in the normal metals induce deterministic spin-transfer torques on the magnet. Additionally, each electron's discrete spin angular momentum causes stochastic fluctuating torques on the antiferromagnet or ferrimagnet. We derive these fluctuating torques. The fluctuation-dissipation theorem holds at high temperatures, including the effects of spin-pumping. At low temperatures, we derive shot noise contributions to the fluctuations.
Spin Current Generation Controlled by the Néel State in a Compensated Ferrimagnet
Institute for Solid State Physics, University of Tokyo（东京大学固体物理研究所）；Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences（中国科学院大学 Kavli 理论科学研究所）；CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences（中国科学院大学 拓扑量子计算卓越中心）；Advanced Science Research Center, Japan Atomic Energy Agency（日本原子能研究开发机构 先进科学研究部）；RIKEN Center for Emergent Matter Science (CEMS)（理化学研究所 涌现物质科学中心）
Observation of Coherently Coupled Cation Spin Dynamics in an Insulating Ferrimagnetic Oxide
许多技术上有用的磁性氧化物是亚铁磁绝缘体，其由化学上不同的阳离子组成。在这里，我们研究了不同的磁性阳离子在亚铁磁性NiZnAl铁氧体（Ni $_{0.65}$ Zn $_{0.35}$ Al $_{0.8}$ Fe $_{1.2}$ O $_4$）在连续微波激发下的自旋动力学。具体来说，我们采用时间分辨的X射线铁磁共振分别探测Fe $^{2+/3+}$和Ni $^{2+}$阳离子在不同的亚晶格网站。我们的研究结果表明，旋进阳离子时刻保持刚性，共线配置内$\approx$ 2 $^\circ$。此外，对于铁氧体中的所有磁性阳离子，有效自旋弛豫在$<$ 10%以内是相同的。因此，我们验证了经常假设的“类铁磁”的动力学共振驱动的亚铁磁氧化物，从不同的阳离子的磁矩旋进作为一个连贯的，集体磁化。
Critical size limits for collinear and spin spiral magnetism in CoCr$_2$O$_4$
CoCr $_2$ O $_4$的多铁性是由于锥形自旋-螺旋磁有序的出现引起了电极化的强度。磁性基态具有复杂的尺寸依赖性行为，当达到临界颗粒尺寸时其崩溃。在这里，磁相稳定性的CoCr $_2$ O $_4$在3.6 - 14.0 nm的尺寸范围内的详细介绍了使用结合的中子衍射与XYZ极化分析和宏观磁化强度测量。我们建立了形成自旋螺旋和亚铁磁结构的临界相干畴尺寸，并揭示了无公度自旋螺旋矢量随颗粒尺寸的演化。我们进一步证实了纳米晶CoCr $_2$ O $_4$在自旋螺旋相中存在铁电极化。
Effect of interfacial spin mixing conductance on gyromagnetic ratio of Gd substituted Y$_{3}$Fe$_{5}$O$_{12}$
由于Y $_3$ Fe $_5$ O $_{12}$及其替代物具有低的本征阻尼，常被用作自旋泵实验中的铁磁层。自旋泵是在铁磁材料和非磁性金属界面产生的界面自旋电流，受自旋混合电导参数$G^{\uparrow\downarrow}$控制。$G^{\uparrow\downarrow}$已被证明可增强铁磁层的阻尼。理论分析表明，$G^{\uparrow\downarrow}$对旋磁比的影响仅来自于其可忽略的虚部。本文研究了$G^{\uparrow\downarrow}$引起的亚铁磁晶格的不同阻尼对Gd取代Y $_3$ Fe $_5$ O $_{12}$旋磁比的影响。
