Spin pumping by higher-order dipole-exchange spin-wave modes

Spin pumping(SP)and inverse spin Hall effect(ISHE)driven by parametrically-excited dipole-exchange spin waves in a yttrium iron garnet film have been systematically investigated.The measured voltage spectrum exhibits a feature of the field-induced transition from parallel pumping to perpendicular pumping because of the inhomogeneous excitation geometry.Thanks to the high precision of the SP-ISHE detection,two sets of fine structures in the voltage spectrum are observed,which can correspond well to two kinds of critical points in the multimode spin-wave spectrum for magnetic films.One is the q=0 point of each higher-order dispersion branch,and the other is the local minimum due to the interplay between the dipolar and exchange interactions.These fine structures on the voltage spectrum confirm the spin pumping by higher-order dipole-exchange spin-wave modes,and are helpful for probing the multimode spin-wave spectrum.

Spin pumping at the Co_2 FeAl_(0.5)Si_(0.5)/Pt interface

Spin pumping at the Co2FeAl0.5Si0.5/Pt and Pt/Co2FeAl0.5Si0.5 interfaces has been studied by ferromagnetic resonance technology(FMR). The spin mixing conductance of the Co2FeAl0.5Si0.5/Pt and Pt/Co2FeAl0.5Si0.5 interfaces was determined to be 3.7×1019m 2and 2.1×1019m 2 by comparing the Gilbert damping in a Co2FeAl0.5Si0.5single film, Co2FeAl0.5Si0.5/Pt bilayer film and a Pt/Co2FeAl0.5Si0.5/Pt trilayer film. Spin pumping is more efficient in the Co2FeAl0.5Si0.5/Pt bilayer film than in permalloy/Pt bilayer film.

Temperature dependence of spin pumping in YIG/NiO(x)/W multilayer

We report the temperature dependence of the spin pumping effect for Y_(3)Fe_(5)O_(12)(YIG,0.9μm)/NiO(tNiO)/W(6 nm)(tNiO=0 nm,1 nm,2 nm,and 10 nm)heterostructures.All samples exhibit a strong temperature-dependent inverse spin Hall effect(ISHE)signal I_(c)and sensitivity to the NiO layer thickness.We observe a dramatic decrease of I_(c)with inserting thin NiO layer between YIG and W layers indicating that the inserting of NiO layer significantly suppresses the spin transport from YIG to W.In contrast to the noticeable enhancement in YIG/NiO(tNiO≈1-2 nm)/Pt,the suppression of spin transport may be closely related to the specific interface-dependent spin scattering,spin memory loss,and spin conductance at the NiO/W interface.Besides,the I_(c)of YIG/Ni O/W exhibits a maximum near the TNof the AF NiO layer because the spins are transported dominantly by incoherent thermal magnons.

Inverse spin Hall effect in ITO/YIG exited by spin pumping and spin Seebeck experiments

Spin currents, which are excited in indium tin oxide(ITO)/yttrium iron garnet(YIG) by the methods of spin pumping and spin Seebeck effect, are investigated through the inverse spin Hall effect(ISHE). It is demonstrated that the ISHE voltage can be generated in ITO by spin pumping under both in-plane and out-of-plane magnetization configurations.Moreover, it is observed that the enhancement of spin Hall angle and interfacial spin mixing conductance can be achieved by an appropriate annealing process. However, the ISHE voltage is hardly seen in the presence of a longitudinal temperature gradient. The absence of the longitudinal spin Seebeck effect can be ascribed to the almost equal thermal conductivity of ITO and YIG and specific interface structure, or to the large negative temperature dependent spin mixing conductance.

Spin pumping through magnetic impurity effect

We propose a simple adiabatic quantum spin pump to generate pure spin current. The spin pump is driven by an ac gate voltage and a time-dependent magnetic impurity potential. It is found that the total pumped spin per cycle exhibits oscillations, whose magnitude decays exponentially with changing strength of the impurity potential. The proposed method may be useful for spintronic applications.

Spin transport characteristics modulated by the GeBi interlayer in Y_(3)Fe_(5)O_(12)/GeBi/Pt heterostructures

For the past few years,germanium-based semiconductor spintronics has attracted considerable interest due to its potential for integration into mainstream semiconductor technology.The main challenges in the development of modern semiconductor spintronics are the generation,detection,and manipulation of spin currents.Here,the transport characteristics of a spin current generated by spin pumping through a GeBi semiconductor barrier in Y_(3)Fe_(5)O_(12)/GeBi/Pt heterostructures were investigated systematically.The effective spin-mixing conductance and inverse spin Hall voltage to quantitatively describe the spin transport characteristics were extracted.The spin-injection efficiency in the Y_(3)Fe_(5)O_(12)/GeBi/Pt heterostructures is comparable to that of the Y_(3)Fe_(5)O_(12)/Pt bilayer,and the inverse spin Hall voltage exponential decays with the increase in the barrier thickness.Furthermore,the band gap of the GeBi layer was tuned by changing the Bi content.The spin-injection efficiency at the YIG/semiconductor interface and the spin transportation within the semiconductor barrier are related to the band gap of the GeBi layer.Our results may be used as guidelines for the fabrication of efficient spin transmission structures and may lead to further studies on the impacts of different kinds of barrier materials.

Influence of pump intensity on atomic spin relaxation in a vapor cell

Atomic spin relaxation in a vapor cell, which can be characterized by the magnetic resonance linewidth(MRL),is an important parameter that eventually determines the sensitivity of an atomic magnetometer. In this paper, we have extensively studied how the pump intensity affects the spin relaxation. The experiment is performed with a cesium vapor cell, and the influence of the pump intensity on MRL is measured at room temperature at zero-field resonance. A simple model with five atomic levels of a Λ-like configuration is discussed theoretically, which can be used to represent the experimental process approximately, and the experimental results can be explained to some extent. Both the experimental and the theoretical results show a nonlinear broadening of the MRL when the pump intensity is increasing. The work helps to understand the mechanism of pump induced atomic spin relaxation in the atomic magnetometers.

Spin-current pump in silicene

We report a theoretical study of pumped spin currents in a silicene-based pump device, where two time-dependent staggered potentials are introduced through the perpendicular electric fields and a magnetic insulator is considered in between the two pumping potentials to magnetize the Dirac electrons. It is shown that giant spin currents can be generated in the pump device because the pumping can be optimal for each transport mode, the pumping current is quantized. By controlling the relevant parameters of the device, both pure spin currents and fully spin-polarized currents can be obtained.Our results may shed a new light on the generation of pumped spin currents in Dirac-electron systems.

Optical pumping and population transfer of nuclear-spin states of caesium atoms in high magnetic fields

Nuclear-spin states of gaseous-state Cs atoms in the ground state are optically manipulated using a Ti：sapphire laser in a magnetic field of 1.516 T, in which optical coupling of the nuclear-spin states is achieved through hyperfine interactions between electrons and nuclei. The steady-state population distribution in the hyperfine Zeeman sublevels of the ground state is detected by using a tunable diode laser. Furthermore, the state population transfer among the hyperfine Zeeman sublevels, which results from the collision-induced modification δa（S·I） of the hyperfine interaction of Cs in the ground state due to stochastic collisions between Cs atoms and buffer-gas molecules, is studied at different buffer-gas pressures. The experimental results show that high-field optical pumping and the small change δa（S · I） of the hyperfine interaction can strongly cause the state population transfer and spin-state interchange among the hyperfine Zeeman sublevels. The calculated results maybe explain the steady-state population in hyperfine Zeeman sublevels in terms of rates of optical-pumping, electron-spin flip, nuclear spin flip, and electron-nuclear spin flip-flop transitions among the hyperfine Zeeman sublevels of the ground state of Cs atoms. This method may be applied to the nuclear-spin-based solid-state quantum computation.

The origin of spin current in YIG/nonmagnetic metal multilayers at ferromagnetic resonance

Spin pumping in yttrium-iron-garnet（YIG）/nonmagnetic-metal（NM） layer systems under ferromagnetic resonance（FMR） conditions is a popular method of generating spin current in the NM layer.A good understanding of the spin current source is essential in extracting spin Hall angle of the NM and in potential spintronics applications.It is widely believed that spin current is pumped from precessing YIG magnetization into NM layer.Here,by combining microwave absorption and DC-voltage measurements on thin YIG/Pt and YIG/NM_1/NM_2（NM_1 =Cu or Al,NM_2 =Pt or Ta）,we unambiguously showed that spin current in NM,instead of from the precessing YIG magnetization,came from the magnetized NM surface（in contact with thin YIG）,either due to the magnetic proximity effect（MPE） or from the inevitable diffused Fe ions from YIG to NM.This conclusion is reached through analyzing the FMR microwave absorption peaks with the DC-voltage peak from the inverse spin Hall effect（ISHE）.The voltage signal is attributed to the magnetized NM surface,hardly observed in the conventional FMR experiments,and was greatly amplified when the electrical detection circuit was switched on.

Miniature quad-channel spin-exchange relaxation-free magnetometer for magnetoencephalography

A miniature quad-channel optically pumped atomic magnetometer(OPM) has been developed based on the spinexchange relaxation-free(SERF) mechanism. With a vapor cell of size 8 mm×8 mm×8 mm, we have incorporated four SERF magnetometer channels, which provides sufficient spatial resolution for magnetoencephalography(MEG). The four channels share the same laser beam for the best cancellation of common mode noise due to laser fluctuations. With gradient measurement, the sensitivities of the four sensors are better than 6 fT/Hz^(1/2), which is also good enough for MEG measurement. The vapor cell is heated to 160℃ by a novel nonmagnetic current-heating structure. Our sensor with high spatial resolution and compact size is particularly suitable for MEG systems.

Study of the optimal duty cycle and pumping rate for square-wave amplitude-modulated Bell–Bloom magnetometers

We theoretically and experimentally study the optimal duty cycle and pumping rate for square-wave amplitudemodulated Bell–Bloom magnetometers.The theoretical and the experimental results are in good agreement for duty cycles and corresponding pumping rates ranging over 2 orders of magnitude.Our study gives the maximum field response as a function of duty cycle and pumping rate.Especially,for a fixed duty cycle,the maximum field response is obtained when the time averaged pumping rate,which is the product of pumping rate and duty cycle,is equal to the transverse relaxation rate in the dark.By using a combination of small duty cycle and large pumping rate,one can increase the maximum field response by up to a factor of 2 or π /2,relative to that of the sinusoidal modulation or the 50% duty cycle square-wave modulation respectively.We further show that the same pumping condition is also practically optimal for the sensitivity due to the fact that the signal at resonance is insensitive to the fluctuations of pumping rate and duty cycle.

Optical pumping nuclear magnetic resonance system rotating in a plane parallel to the quantization axis

A model of an optical pumping nuclear magnetic resonance system rotating in a plane parallel to the quantization axis is presented. Different coordinate frames for nuclear spin polarization vector are introduced, and theoretical calculation is conducted to analyze this model. We demonstrate that when the optical pumping nuclear magnetic resonance system rotates in a plane parallel to the quantization axis, it will maintain a steady state with respect to the quantization axis which is independent of rotational speed and direction.

Optical pumping nuclear magnetic resonance system rotating in a plane parallel to the quantization axis

Requested by the authors, the article entitled ＂Optical pumping nuclear magnetic resonance system rotating in a plane parallel to the quantization axis＂, published in Chinese Physics B, 2017, Vol. 26, Issue 9, Article No. 093301, has been withdrawn from the publication. The authors found that the axes in the rotating frame xy＇z are not all time-invariant, so Eq. （12） obtained from Eq. （11） is incorrect, and the conclusion is inaccurate.

Ni/Pt异质结界面的自旋阻塞效应

相比于电荷流的高功耗,自旋流可以高效地传输能量与信息的同时避免焦耳热的产生,因此基于自旋流的电子器件成为未来电子信息器件研发的重要方向之一.自旋流及其输运现象的相关研究是自旋电子学器件的开发基础.本文着眼于铁磁金属镍(Ni)与非磁重金属(Pt)构建的异质结结构,研究了异质结界面的自旋输运特性,发现其对扩散自旋流的全阻塞效应.本工作以基于钇铁石榴石(yttrium iron garnet,YIG)的YIG/Ni/Pt三层器件开展,采用自旋泵浦技术激发扩散自旋流注入到镍中,同时检测与分析器件中的逆自旋霍尔电压,并与YIG/Ni双层器件中的信号进行对比分析.结果证明YIG/Ni/Pt三层器件中的铂金属层仅起分流作用而对逆自旋霍尔电流无贡献,即镍层中的扩散自旋流被阻塞于Ni/Pt异质结界面.本工作加深了对界面处自旋流输运的认识,铁磁性金属/非磁重金属自旋流阻塞界面的发现也为自旋电子器件的设计及新功能开发提供了新的思路与手段.

不同轴向游隙下涡轮泵球轴承动态特性研究

针对不合理的轴向游隙会恶化轴承的工作环境、降低轴承寿命并影响到涡轮泵球轴承-转子系统的稳定运行的问题,根据轴向游隙与接触角间的数学关系,将轴向游隙引入轴承部件的几何分析中,并基于Hertz接触定理和各部件间的相互作用,建立了考虑轴向游隙的涡轮泵球轴承动态特性计算模型。依据部件间变形几何关系进行变量缩减,简化了解析形式刚度矩阵的建立流程,降低了迭代计算的复杂度。以涡轮泵某型号球轴承为例,对不同载荷工况下轴向游隙对接触载荷、刚度和旋滚比的影响进行计算分析。计算结果表明:当轴向游隙增大,滚球与内、外滚道间的接触载荷均会降低,轴向刚度增大,径向刚度减小,所有滚球旋滚比均会升高,各滚球旋滚比之间的差异也会增大;当轴承所受径向力较大或转速较高时,轴向游隙越大,轴承刚度和旋滚比随外载荷改变而变化的程度越明显。所建立的模型和动力学典型算例的计算结果偏差最大不超过2.02%,整体偏差较低,证明了所建立的模型在轴承动态参数计算上的有效性和稳定性,同时也表明了在数值求解及迭代矩阵建立上采取的简化措施是可行的。

光泵磁力计-脑磁图的应用研究进展

脑磁图作为一种无创获取大脑信号的新技术,可精准反映大脑的神经活动,但传统脑磁图设备的低温超导环境与高运维成本限制了这一技术的发展。光泵磁力计作为一种新型的磁场强度检测装置,具有造价成本低、信噪比高、无需低温液氦冷却等诸多优势,有望助推脑磁图技术广泛应用。在陈述脑磁图概念的基础上,从技术角度说明光泵磁力计-脑磁图系统的实现原理,梳理该系统存在的命名问题,并从神经语音解码、脑磁源重建、功能神经成像、脑机接口和临床辅助等方面综述了该系统的应用研究进展,总结该新型脑磁图系统独特优势,并展望这种技术的未来潜在应用,最后分析了目前此类研究中可能存在的问题。

激光泵浦铯-氦磁强计的噪声抑制

介绍了一种利用单模激光进行泵浦的铯-氦磁强计。由于单模激光比铯元素放电灯具有更高的泵浦效率,这种铯-氦磁强计得到了比传统的放电灯铯-氦磁强计更强的磁共振信号。通过测量各试验因素中引入的磁噪声,发现激光的光功率涨落是目前磁噪声的主要来源;通过分析信噪比与光强的关系,得到了最优化的光强;通过主动光强降噪技术,在最佳试验条件下,铯-氦磁强计的噪声峰峰值可以优于0.02 nT。结果表明,通过提升激光功率的稳定性,激光泵浦式的铯-氦磁强计非常有潜力得到比质子磁强计更高的准确度,可作为恒定弱磁场计量标准的新一代主标准器。

SERF原子自旋惯性测量检测误差分析及抑制

在无自旋交换弛豫(SERF)原子自旋惯性测量装置中,检测系统的性能是决定输出信号灵敏度和稳定性极限的关键因素。为有效抑制SERF原子自旋惯性测量的低频随机噪声,在横向电子自旋极化率稳态解和旋光角表达式的基础上,建立检测相关的输出信号误差机理模型,明确了检测系统影响最终测量信号噪声的主要因素。研究结果表明:检测光入射气室时的初始光强作为信号背景直接引起刻度系数的波动而非作用于电子自旋,而检测光的非理想线偏振导致电子自旋产生横向抽运效果和横向光频移作用,从而引入测量误差。针对检测系统影响测量信号噪声的主要参数,设计了参数优化路径:先通过优化检测光频率,提高惯性测量刻度系数,后通过检测光功率的优化,减小横向抽运效应、横向光频移作用及检测光背景波动。实验表明:通过对比输出信号的Allan方差,优化后SERF原子自旋惯性测量的零偏不稳定性减小了1.8倍,速率斜坡噪声系数从0.124 (°)/h^(2)减小至0.041 (°)/h^(2),达到了抑制测量信号低频随机噪声的效果。

超极化气体肺部磁共振成像

磁共振成像(MRI)技术具有非侵入、无放射性的特点,在临床疾病诊断中具有独特的优势,但是肺部空腔的特殊结构使传统质子MRI无法对其直接成像.自旋交换光抽运(SEOP)方法可以使惰性气体原子的极化度增强4个量级以上,从而使肺部的气体MRI成为可能.该文介绍了超极化惰性气体肺部MRI的最新研究进展,包括超极化气体磁共振相关参数的测量方法、肺部通气结构成像、肺部气体交换功能成像,同时比较了常用于肺部MRI气体的优点和缺点.