具有倾斜极化层的自旋阀结构中磁翻转以及磁振荡模式的微磁模拟

基于自由层与钉扎层均为垂直磁各向异性的自旋阀结构,采用微磁学模拟与傅里叶分析相结合的技术,研究了极化层磁矩小角度倾斜情形下自由层磁矩的进动翻转特性.通过沿样品垂直膜面方向同时施加电流与磁场,观察到自由层磁矩垂直膜面方向分量的平均值随磁场的演化翻转曲线中出现了多个凹槽.模拟研究结果表明:在一定的电流范围内,凹槽出现的位置与电流大小无关;而在固定的应用电流下,凹槽出现的位置将会受到样品厚度的影响;在凹槽区域内,非一致进动模式、自旋驻波模式、局域自旋波模式等多种磁振荡模式被激发.通过傅里叶分析,得到了各种磁振荡模式的频谱,频谱中的频率分布体现出了倍频以及间谐波的频率特性.     

磁子霍尔效应

霍尔效应是凝聚态领域中古老却又极具潜力的研究领域,其起源可以追溯到数百年前. 1879年,霍尔发现将载流导体置于磁场中时,磁场带来的洛伦兹力将使得电子在导体的一侧积累,这一新奇的物理现象被命名为霍尔效应.之后,一系列新的霍尔效应被发现,包括反常霍尔效应、量子霍尔效应、自旋霍尔效应、拓扑霍尔效应和平面霍尔效应等.值得注意的是,霍尔效应能够实现不同方向的粒子流之间的相互转化,因此在信息传输过程中扮演着重要的角色.在玻色子体系(如磁子)中,相应的一系列磁子霍尔效应也被发现,他们共同推动了以磁子为基础的自旋电子学的发展.本文回顾了近年来在磁子体系中的霍尔效应,简述其现代半经典的处理方法,包括虚拟电磁场理论和散射理论等.并进一步介绍了磁子霍尔效应的物理起源,概述了不同类型磁子的霍尔效应.最后,对磁子霍尔效应的发展趋势进行了展望.     

光格中玻色-爱因斯坦凝聚的自旋磁子和自旋波

研究了一维光格中旋量玻色—爱因斯坦凝聚体的自旋磁子和自旋波。求出了自旋磁子和自发磁化强度。用经典方法求得了均匀体系的自旋波和能级以及激光调制下的自旋波和能级。特别是在连续极限近似下,求得了马丢函数波及其能级。     

光格中玻色-爱因斯坦凝聚的自旋磁子和自旋波

研究了一维光格中旋量玻色—爱因斯坦凝聚体的自旋磁子和自旋波。求出了自旋磁子和自发磁化强度。用经典方法求得了均匀体系的自旋波和能级以及激光调制下的自旋波和能级。特别是在连续极限近似下,求得了马丢函数波及其能级。     

光格中玻色-爱因斯坦凝聚的自旋磁子和自旋波北大核心CSCD

研究了一维光格中旋量玻色—爱因斯坦凝聚体的自旋磁子和自旋波.求出了自旋磁子和自发磁化强度.用经典方法求得了均匀体系的自旋波和能级以及激光调制下的自旋波和能级.特别是在连续极限近似下,求得了马丢函数波及其能级.     

在尺寸受限体系中的磁斯格明子

磁性斯格明子是具有拓扑保护性质的纳米尺度磁涡旋结构。由于其具有尺寸小、稳定性高和可操控等粒子特性,在未来构建高密度、高速度、低能耗、非易失性磁存储器件方面具有潜在的应用价值,引起了人们的广泛关注。文章就斯格明子产生的基本原理、性质,尤其是在尺寸受限条件下的稳定性机制、实空间观察、器件应用及面临的挑战等进行简单阐述。     

声表面波-自旋波耦合及磁声非互易性器件

声表面波是激发和控制自旋波的一种新兴手段,不仅激励效率高,而且传输长度可以达到毫米量级,通过引入磁声耦合还可以打破时空反演对称性,实现声表面波的非互易传播.本文对不同类型的磁声耦合的物理机制进行了梳理,对比了磁弹性耦合、自旋-涡度耦合(包括非磁性层注入交变自旋流和磁性材料自身的Barnett效应),以及磁-旋转耦合在不同模式的声表面波激发下的等效驱动磁场,讨论了这些等效驱动场的角度依赖性,以及相应功率吸收的频率依赖性.这为在实际应用中区分和利用各种磁声耦合机制提供了理论支持.此外,本文还介绍了利用磁声耦合实现声表面波非互易性传输的两种主流手段,包括利用手性失配效应和引入具有非互易性自旋波色散关系的磁结构,对比并讨论了它们各自的物理机制和优劣势,希望为设计和发展基于磁声耦合的固态声学隔离器、环形器提供参考.     

铁磁纳米线中磁化强度的磁怪波

本文介绍了铁磁纳米线中磁化强度的一些新激发态,包括各向同性铁磁的Akhmediev呼吸子、Kuznetsov-Ma孤子和怪波、自旋极化电流驱动下各向异性铁磁纳米线中的怪波动力学.在各向同性情况下,展示了形如四片花瓣的磁孤子的空间周期过程和自旋波背景的局域化过程;在极限情况下,得到了磁怪波解并阐明了其形成机制.在各向异性...     

磁子学中的拓扑物态与量子效应

近年来,随着物联网、云计算、大数据以及人工智能等新兴技术的快速发展,人们对计算能力的要求越来越高.传统半导体器件在小型化、节能和散热等方面面临着巨大的挑战,因此亟需寻找一种全新的信息载体代替电子进行信息传输与处理.自旋波是磁矩进动的集体激发,其量子化的准粒子称为磁子.磁子的传播不依赖于传导电子的运动,因此不会产生焦耳热,能够克服日益显著的器件发热问题,因此磁子器件在低功耗信息存储与计算领域具有重要的应用前景.本文介绍磁子学近年来的一些重要研究进展,主要包括自旋波的手性传播,自旋波与磁孤子非线性散射导致的磁子频率梳,磁孤子的拓扑边界态和高阶角态,以及磁子量子态、基于磁子的混合量子体系和腔磁子学.最后,对磁子学的未来发展趋势及其前景进行分析与展望.     

有机自旋阀的磁电阻性质研究

考虑到有机半导体中极化子和双极化子特殊的电荷-自旋关系,从自旋扩散方程和欧姆定律出发,理论研究了"铁磁/有机半导体/铁磁"有机自旋阀结构中的磁电阻性质.计算发现,磁电阻在数值上随有机半导体层中极化子比率的增加而增大,随有机半导体层厚度的增加而迅速减小.同时发现自旋相关界面电阻能在很大程度上提高系统的磁电阻.讨论了铁磁层和有机半导体电导率比率、铁磁层极化率等对系统磁电阻性质的影响. 关键词： 磁电阻 有机自旋电子学 极化子     

Squeezing States of Magnons in a Ferromagnet

In this paper, we conduct an investigation into magnon self-squeezing states in a ferromagnet. In these states, the quantum fluctuations of the spin components can be lower than the zero-point quantum fluctuations of the coherent states. Through calculating the expectation values of spin fluctuations we gain the condition of achieving magnon self-squeezing. We introduce the mean-field theory for dealing with the nonlinear interaction term of Hamiltonian of magnon system.     

From microelectronics to spintronics and magnonics

In this review, the recent developments in microelectronics, spintronics, and magnonics have been summarized and compared. Firstly, the history of the spintronics has been briefly reviewed. Moreover, the recent development of magnonics such as magnon-mediated current drag effect (MCDE), magnon valve effect (MVE), magnon junction effect (MJE), magnon blocking effect (MBE), magnon-mediated nonlocal spin Hall magnetoresistance (MNSMR), magnon-transfer torque (MTT) effect, and magnon resonant tunneling (MRT) effect, magnon skin effect (MSE), etc., existing in magnon junctions or magnon heterojunctions, have been summarized and their potential applications in memory and logic devices, etc., are prospected, from which we can see a promising future for spintronics and magnonics beyond micro-electronics.     

Magnon bands in twisted bilayer honeycomb quantum magnets

We study the magnon bands of twisted bilayer honeycomb quantum magnets using linear spin wave theory. Although the interlayer coupling can be ferromagnetic or antiferromagnetic, we keep the intralayer one ferromagnetic to avoid possible frustration. For the interlayer ferromagnetic case, we find the magnon bands have similar features with the corresponding electronic energy spectrums. Although the linear dispersions near the Dirac points are preserved in the magnon bands of twisted bilayer magnets, their slopes are reduced with the decrease of the twist angles. On the other hand, the interlayer antiferromagnetic couplings generate quite different magnon spectra. The two single-layered magnon spectra are usually decoupled due to the opposite orientations of the spins in the two layers. We also develop a low-energy continuous theory for very small twist angles, which has been verified to fit well with the exact tight-binding calculations. Our results may be experimentally observed due to the rapid progress in two-dimensional magnetic materials.     

The phenomenon of even bulk modes variance in a ferromagnetic A--A bilayer system

The eigenproblems of spin waves in a symmetrical ferromagnetic bilayered system with periodic boundary conditions are solved using the interface-rescaling approach (IRA). The results show that interface coupling between two sublayers would not change the excitation energy of odd bulk modes, but change excitation energy of even bulk modes. We call this peculiar phenomenon the phenomenon of even bulk mode variance (PEBMV). There are two kinds of mechanisms which cause PEBMV: phase reversal and phase translation of the magnon at the interface, corresponding, respectively, to the antiferromagnetic and ferromagnetic interface coupling cases. PEBMV embodies the selective effect of the interface on different bulk magnons.     

Bose–Einstein condensation of magnons in ferromagnetic thin films

Experimental evidence for Bose–Einstein condensation (BEC) of magnons at room temperature in a thin film of yttrium iron garnet (YIG) excited by parallel pumping is already available and different features of the experimental results have been explained qualitatively [Nature 443, 430 (2006)]. In the present work, we explain quantitatively different aspects of this experimental observation through spin wave treatment. In the case of parallel pumping field, we have developed a formula for the time required for the formation of magnon BEC in a thin film of ferromagnetic material. This relation is found to be in good agreement with known experimental results. In a similar treatment we predict the condition for the formation of BEC of magnons in the case of perpendicular pumping.     

计算顺磁-铁磁相变临界磁场的一种方法

利用线性自旋波方法并结合Hellmann-Feynman定理引入一种计算量子磁性系统临界磁场的方法.计算两种特殊模型的临界磁场,并将理论结果与数值结果进行比较,理论值与数值结果高度吻合,验证了理论方法的准确性.     

Magnon Blockade and Magnon–Atom Entanglement Induced by a Qutrit Coupled to a Ferromagnetic YIG Sphere

Hybridized magnonic–photonic systems promise novel applications for future information processing technologies. Here, a hybrid magnonic system comprising of a qutrit (Λ-type three-level atom) and a ferromagnetic YIG sphere is considered. Indeed, the whole system is driven by two light fields under the influence of the thermal environment. The indirect magnon–atom interaction is established via the virtual photon exchange. The associated Lindblad master equation is derived and its solution is found to investigate the nonclassical feature, especially in the steady-state solution. Generally, the system shows considerable nonclassicality, that is, strong magnon antibunching and magnon blockade. In fact, the feasibility of using such a hybrid system to prepare a single-magnon source based on magnon blockade effects we theoretically demonstrated. Besides, the considered system may be exploited to generate robust and stable magnon–atom entanglement. The appearance of magnon blockade and magnon–atom entanglement in the Λ-type atom may have its origin in the fact that the atom is trapped in different superposition states, induced by the quantum interference phenomenon. The proposed model and the corresponding results may open up an intriguing prospect to prepare a single-magnon source and provide further benefits through concatenating with photons in optomagnonic systems.     

自旋Seebeck效应简介

自旋电子学作为一个新兴的学科,是未来电子学发展的重要方向之一.而近年来发现的自旋泽贝克（Seebeck）效应则为自旋电子学的研究提供了不少新现象.文章通过对自旋Seebeck效应的一些科研进展的介绍,较详尽地阐明了自旋Seebeck效应的定义和常用的利用逆自旋霍尔（Hall）效应来进行观测的机制与方法,并对不同种类材料中的自旋Seebeck效应及其可能的成因进行了分析介绍.