An Archimedean screw is a classical pump that exploits the equivalence of rotation and translation in helices. Similarly, a spin spiral texture can pump charge and spin by rotating at a frequency $ω$. In the present paper, we study these pumping phenomena within a microscopic quantum model by both perturbation theory and numerical simulations. Inside the spiral region, the spin polarization and charge current are linear in $ω$ whereas the spin current is $ω^2$ for small $ω$. We find that the charge current is related to the mixed momentum-phason Berry phase, which can be viewed as a novel approximate realization of a Thouless pump. It is nearly quantized in spirals with short pitch $λ$ but decays with $λ^{-1}$ for longer pitches, unlike true Thouless pumps or Archimedian screws. Moreover, we study the onset of non-adiabaticity (large $ω$), the impact of attached non-magnetic or magnetic contacts, and the real-time evolution of the transport observables. Finally, we analyze the effects of disorders which, surprisingly, might enhance the spin current but suppress the charge current.
Italian Institute of Technology（意大利理工学院）；University of Genoa（热那亚大学）；University of Groningen（格罗宁根大学）；RIKEN Center for Emergent Matter Science (CEMS)（理化学研究所 emergent matter science 中心）；Fundamental Quantum Science Program (FQSP), TRIP Headquarters, RIKEN（理化学研究所 基础量子科学计划（FQSP）TRIP总部）；Quantum Materials Theory（量子材料理论）
Controlled spin transport in magnetic stacks is required to realize pure spin current-driven logic and memory devices. The control over the generation and detection of the pure spin current is achieved by tuning the spin to charge conversion efficiency of the heavy metal interfacing with ferromagnets. Here, we demonstrate the direct tunability of spin angular momentum transfer and thereby spin pumping, in CoFeB/Pt stack, with interfacial magnetic anisotropy. The ultra-low thickness of CoFeB thin film tilts the magnetic easy axis from in-plane to out-of-plane due to surface anisotropy. The Ferr…
Non-Reciprocal Spin Pumping in Asymmetric Magnetic Trilayers
在磁性三层系统中，自旋泵通常被视为一种相互作用机制，其特征在于两个界面都有一个独特的自旋混合电导。然而，在材料中存在不同类型的界面的情况下，这种假设是有问题的。在这里，我们提出了一个一般的理论分析自旋泵的情况下，有一个以上的独特的接口。该理论被应用于分析层分辨铁磁共振实验上的三层系统Ni $_{20}$ Fe $_{80}$ /Ru/Fe $_{49}$ Co $_{49}$ V $_2$的Ru间隔层厚度是不同的，以调整间接交换耦合。结果表明，不同磁性层的三层系统中的自旋泵是非互易的，不同界面的自旋泵感生阻尼之间有很大的差异。我们的研究结果对基于磁性多层材料的自旋电子器件的动力学研究具有重要意义。
Spin transfer torque and spin pumping are central reciprocal phenomena in spintronics. These phenomena occur in hybrid systems of normal metals and magnets. Spin transfer is the conversion of spin currents in metals to a torque on the magnetization of magnets. Spin pumping is the emission of spin currents from precessing magnets. Here, we demonstrate a general way to understand these effects within a quantum out-of-equilibrium path-integral model. Our results agree with known expressions for spin transfer and spin pumping in terms of transverse (mixing) conductances when there are no fluctuati…
Chiral spin pumping is the generation of a unidirectional spin current in half of ferromagnetic films or conductors by dynamic dipolar stray fields from close-by nanomagnets. We formulate a general theory of long-range chiral interactions between magnets mediated by unidirectional traveling waves, e.g., spin waves in a magnetic film or microwaves in a waveguide. The traveling waves emitted by an excited magnet can be perfectly trapped by a second, initially passive, magnet by a dynamical interference effect. When both magnets are excited by a uniform microwave, the chiral interaction between t…
The adiabatic topological pumping is proposed by periodically modulating a semiconductor nanowire double-quantum-dot chain. We demonstrate that the quantized charge transport can be achieved by a nontrivial modulation of the quantum-dot well and barrier potentials. When the quantum-dot well potential is replaced by a time-dependent staggered magnetic field, the topological spin pumping can be realized by periodically modulating the barrier potentials and magnetic field. We also demonstrate that in the presence of Rashba spin-orbit interaction, the double-quantum-dot chain can be used to implem…
The combination of parametric pumping and spin-transfer torque is a powerful approach that enables high-level control over magnetic excitations in thin-film ferromagnets. The excitation parameters, such as pumping power and external field strength, affect the instabilities of individual magnon modes. We theoretically explore how the simultaneous effects of parametric pumping and spin transfer torque influence these magnetic instabilities in a thin-film ferromagnet. Within the Landau-Lifshitz-Gilbert framework, we perform micromagnetic simulations of magnon excitations in yttrium iron garnet by…
A mechanism of current-induced magnetization reversal based on the parametric resonance is described. The source of the magnetization reversal is a current-induced magnetic field, which is applied perpendicularly to the easy axis of magnetic anisotropy of a ferromagnetic nanomagnet. The current-induced magnetic field was measured in a FeCoB nanomagnet to be 60 Gauss at a current density of 65 mA/um2. Two mechanisms of the magnetization reversal are described and calculated. The first mechanism is the reversal by a RF electrical current, which modulated at a frequency close to the precession fr…
Spin pumping damping and magnetic proximity effect in Pd and Pt spin-sink layers
我们研究了顺磁层（Pd，Pt）与铁磁Ni $_{81}$ Fe $_{19}$薄膜直接和间接接触时所产生的自旋泵浦阻尼。我们发现在直接接触Ni $_{81}$ Fe $_{19}$ /（Pd，Pt）结中，界面相关的吉尔伯特阻尼增强$Δα$与重金属自旋吸收层厚度t $_\textrm{N}$近似线性相关，而当Ni $_{81}$ Fe $_{19}$和（Pd，Pt）被\unit [3]{nm} Cu隔开时，则观察到指数相关.我们属性的准线性厚度依赖性的存在下，在Pt，Pd附近的界面与Ni $_{81}$ Fe $_{19}$，量化使用X-射线磁性圆二色性（XMCD）测量的感应力矩。我们的结果表明，在这些系统中，纯自旋流的散射是构型相关的，不能用单一的特征长度来描述。
We investigate magnetization dynamics in asymmetric interlayer exchange coupled Py/Ru/Py trilayers using both vector network analyzer-based and electrically detected ferromagnetic resonance techniques. Two different ferromagnetic resonance modes, in-phase and out-of-phase, are observed across all three regimes of the static magnetization configurations, through antiparallel alignment at low fields, the spin-flop transition at intermediate fields, and parallel alignment at high fields. The nonmonotonic behavior of the modes as a function of the external field is explained in detail by analyzing…
Probing Interfacial Spin Dynamics and Temperature Dependent Asymmetry in Spin Pumping Across Ni80Fe20/Cu/Cr1.12Te2 Interfaces
Department of Physics, Indian Institute of Technology Kanpur（印度坎普尔理工学院物理系）；Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University（南洋理工大学国立教育学院自然科学与科学教育）
We study the effects of the coupling between magnetization dynamics and the electronic degrees of freedom in a heterostructure of a metallic nanomagnet with dynamic magnetization coupled with a superconductor containing a steady spin-splitting field. We predict how this system exhibits a non-linear spin torque, which can be driven either with a temperature difference or a voltage across the interface. We generalize this notion to arbitrary magnetization precession by deriving a Keldysh action for the interface, describing the coupled charge, heat and spin transport in the presence of a precess…
Optical pump-probe techniques are used to generate and measure electron spin polarization in a gallium arsenide epilayer in which the electron spin coherence time exceeds the mode-locked laser repetition period. Resonant spin amplification occurs at magnetic fields at which the electron spin polarization excited by successive laser pulses add constructively. Measurements of Kerr rotation as a function of applied magnetic field reveal nuclear spin polarization that aligns either with or against the external magnetic field depending on whether the applied magnetic field is being decreased or inc…
