News

A Fast Random Number Generator based on MTJ

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Random numbers are essential in many information technologies, especially those concerning cyber security. Nowadays, most random numbers are the pseudo random numbers generated by mathematical algorithms. A compact, fast, and true random number generator (TRNG) is highly desirable.

It has been proposed that a TRNG can be constructed from a magnetic tunnel junction (MTJ), utilizing the thermal activated random magnetization switching. …

张家斌、陈锡恒硕士论文答辩

与会者合影2

2022年5月23日,张家斌和陈锡恒两位同学成功举行了线上硕士论文答辩,论文题目分别是《基于COMSOL的时域与频域微磁学模拟研究》和《基于微磁学理论的磁结构调控与应用》。答辩委员会成员包括同济刘要稳教授、苏州纳米所曾中明研究院、天津大学兰金副教授、复旦大学吴义政教授。

两位同学经过共两个多小时的报告和质询答辩,答辩委员会一致建议授予张家斌和陈锡恒两位同学硕士学位。恭喜张家斌和陈锡恒!



A Hopfield neural network in magnetic films with natural learning

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In order to develop its ultimate potential, artificial intelligence must shift from the software-based towards hardware-based neuromorphic algorithms. For the artificial neural network, it requires materials and devices that are capable of emulating neuron-like activation and synapses with reprogrammable weights. To the best of our knowledge, all existing approaches in implementing synapses require external computation to train the network. …

An adiabatic method to train Binary Neural Networks

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We proposed a new training method to realize binary neural networks. [1] This method can successfully train a conventional neural network into a binary one, where the neuron activations and/or weights take binary values of (+1 and -1). 

This work turned out to be compeletely in the field of Computer Science. It has little to do with Physics except the adiabatic method that is often used in physics studies. …

Skew scattering and side jump of spin wave across magnetic texture

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Continuing our investigations on the interplay between spin wave and magnetic texture, we proceed to simplify their interplay by treating both the magnetic texture and spin wave as particle-like objects, and their interaction becomes a particle-colliding process.

In magnetic system, spin wave and magnetic texture can be regarded as two types of elementary excitations with fast and slow dynamics upon homogenous background. …

陈恭正硕士论文答辩

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2020年7月25日,陈恭正同学成功举行了他的硕士论文答辩,论文题目是《铁电畴壁动力学的数值模拟研究》。陈恭正的答辩委员会成员包括同济刘要稳教授,成都电子科大严鹏教授,以及天津大学兰金教授。

经过一个多小时的报告和质询答辩,答辩委员会一致建议授予陈恭正同学硕士学位。恭喜陈恭正!


Loop theory for scattering in cavities

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Continuing our pursuit in understanding coupled systems, we developed a simple graphical loop theory in calculating transmission and reflection for a general coupled systems with multiple internal modes. This graphical method is so simple that no calculation is needed.

For its important role in the fundamental physics as well as its intriguing docking with the quantum information technology, understanding and manipulating the light-matter interaction ranging from macroscopic scale to nanoscale is a long-lasting topic in many disciplines of physics, including the condensed matter physics, atomic, molecular and optical physics. …

Spin wave computing

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The two main issues of the present computing technology are the increasingly severe energy dissipation and the limited computing speed. The origin of both issues can be traced back to the von-Neumann computing architecture, in which the data storage and processing are separately realized in the memory and the central processing unit (CPU). The necessity of communicating between them via the data bus, aka the von-Neumann bottleneck, not only decreases the computing speed, but also wastes significant amount of energy. 

New mechanism for dissipative coupling

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This work started last October during a KITS workshop held in Beijing. During the workshop, Prof. Can-ming Hu from University of Manitoba in Canada reported a non-typical energy level crossing [1], the so-called level attraction, in a YIG-cavity system. The level attraction is very different from the typical repulsive anti-crossing whenenver two energy levels intersecting each other. 

Such level attraction behavior is very similar to the two precessing ferromagnets coupled via spin-pumping and spin-transfer torque studied more than a decade ago by Prof. Yaroslav Tserkovnyak [2]. …

Spin X Workshop

Spin X Program

The first Spin X Workshop was successfully held on Oct. 7th, 2019 in Baolong Hotel, Shanghai. Ten invited speakers from China, Japan, and The Netherlands shared their research ideas on spintronics  ranging from spin mechanics, spin cavitronics, to topological effects in magnetic systems. 

The workshop atmosphere is lively with prolonged hot discussions, and extended for more than 2 hours than planned. 

We would like to thank all the speakers for their contributions to the successful gathering and exchange of ideas. 

余伟超博士赴日本东北大学任助理教授

余伟超博士将于2019年4月1日起加入日本东北大学金属研究所,担任助理教授。

余伟超博士于2013年9月加入本课题组,并于2018年6月份以出色的表现博士毕业。在赴日本履职之前,在本课题组继续从事了大半年的博士后研究。

感谢余伟超博士近六年来在复旦的出色工作,并预祝他在日本期间能够继续不断的做出优秀科研成果。

Sailing a magnetic domain wall by polarized spin waves

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Weichao and Jin had their fourth joint paper on controlling antiferromagnetic domain wall with polarized spin waves. This paper is recently published on Physical Review B (link). 

In this paper, we continue to explore the possibilities of making use of spin wave polarization in antiferromagnet. We find that the antiferromagnetic domain wall can be pushed forward when the injected spin waves is polarized along one specific linear direction, while is unaffected when  injecting the orthogonal polarization. …

兰金博士加入天津大学

兰金博士今年8月从复旦大学博士后流动站出站,结束了他学术生涯中从学生到老师的重要过度阶段,现为天津大学物理系副教授。

感谢兰金博士这四年来在复旦的出色工作,并预祝他在天津大学能够继续不断的做出优秀科研成果。

Energy storage via toplogical spin textures

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Magnetic structures have been studied extensively in the past decades, mostly concentrated in information storage, and information processing more recently. However, the exploration of the capability of magnetic structure beyond such information related applications is still lacking. Through collaboration with Prof. Yaroslav Tserkovnyak, we introduce a novel idea of using the topological nature of spin textures for energy storage, i.e. a spin battery. …

徐梵清、赵元晟本科毕业论文组内答辩

徐梵清 - 2018

2018年6月1日,2014级的徐梵清、赵元晟两位物理系本科生在组内报告了各自的本科毕业论文。他们的论文题目分别是《深入探讨 Cherenkov radiation 的物理及应用》、《磁振子弛豫与扩散的研究》。


原本每人15分钟的答辩最终都延长到了超过一个小时,最终两人的答辩超过三小时。报告和答辩过程中,两位同学与组内其他成员进行了充分富有成效的讨论。

赵元晟 - 2018


最终,徐梵清、赵元晟同学两位顺利通过答辩。毕业后,两位同学都将出国留学,预祝二位同学学业有成!


右上图:徐梵清正在报告

右下图:赵元晟正在报告


余伟超博士论文答辩

Weichao defense poster

2018年5月30日,余伟超同学成功举行了他的博士论文答辩。伟超的博士论文题目是《基于磁结构的自旋波动力学》,撰写的博士论文长达300页,囊括了伟超近五年博士生涯的许多研究成果。


伟超的答辩委员会阵容强大,由北师大夏钶教授,复旦金晓峰、吴义政、高春雷教授,同济刘要稳教授,南大吴镝教授,以及北航于海明教授等7为教授组成。


经过一个多小时的报告和质询答辩,答辩委员会一致建议授予余伟超同学博士学位。恭喜余伟超!


下面照片(左起):刘要稳、高春雷、金晓峰、夏钶、余伟超、肖江、于海明、吴义政、吴镝

Weichao defense group

Rashba Spin-orbit Magnetoresistance by interface engineering

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The spin Hall magnetoresistance (SMR) is a magnetoresistance (MR) effect in a heavy metal/ferromagnetic insulator bilayer structure. In SMR, the longitudinal resistance of the heavy metal depends on the orientation of the magnetization in the ferromagnetic insulator, and more specifically depends on the projection of the magnetization to the plane spanned by the current direction and the interface normal. …

Antiferromagnetic domain wall polarizing spin waves

spin wave polarizer

Jin and Weichao had their third joint paper on manipulating spin wave polarizations using antiferromagnetic doamin walls. This paper is recently published on Nature Communications (link). 

In this paper, we extend our explorations on novel spin wave devices to functional units that harness the polarization degree of freedom of spin waves. We proposed that the antiferromagnetic domain wall can act as a spin wave polarizer and a spin wave retarder --- two basic polarization manipulation components, thus realizes the full control of the polarization degree of freedom of spin waves, mimicking their optical counterparts.

蔡畅嘉毕业论文组内答辩

IMG 20170606 091803

2013级本科生蔡畅嘉毕业论文今天组内答辩,蔡畅嘉的毕业论文题目是《基于马尔科夫过程的交通决策》。

蔡畅嘉毕业后将赴美国留学,预祝他学业有成!



Spin Summit 2017 Workshop

Spin Summit 2017 - Group Photo

Spin Summit 2017 is the first workshop of the Spin Summit series focusing on the fundamental and applied aspects of spintronics. 

The meeting will take place in August 2017 in the scenic mountain of Jinggangshan, Jiangxi Province, China, which is far away from noisy metropolitan areas and an ideal location for escaping the heat wave at the height of summer. The aim of the workshop is to promote effective and mutually beneficial interactions among participants with plenty of formal and informal discussion time

Spin-Wave Fiber

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Weichao and Jin had their second joint paper on spin wave fiber, published on Physical Review B (Rapid Communications) [link]. In the paper, we continued our pursuit of novel spin wave devices. In this case, we propsoed a spin wave fiber that can transmit spin waves via total reflections at magnetic domain walls (see below), mimicing the optical fiber.

Magnonics is promising for the next generation energy-saving information technology and hence attracted increasing attention of broad researchers in recent years. …

Spin-Wave Diode

Spin Wave Circuits

Jin and Weichao had their joint paper on spin wave diode published on Physical Review X [link]. In the paper, we proposed a novel design of rewritable magnonics hardware architecture and the demonstration of a spin wave diode upon this design.

Magnonics is promising for the next generation energy-saving information technology and hence attracted increasing attention of broad researchers in recent years. The aim of magnonics is to achieve unified information storage and processing using magnons, or spin waves, which are collective quasi-particle excitations of the magnetic moments and can propagate without much energy dissipation. …

Spin Hall effect by surface roughness

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Lingjun had his paper about inducing spin Hall effec by merely rough surface of metallic thin film published on Physical Review B 91, 045407 (2015).

The spin Hall and its inverse effects, driven by the spin orbit interaction, provide an interconversion mechanism between spin and charge currents. Since the spin Hall effect generates and manipulates spin current electrically, to achieve a large effect is becoming an important topic in both academia and industries. …

New exaplaination for the 'spin Hall magnetoresistance'

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Vahram had his paper about intrinsic magnetoresistance in metal films on ferromagnetic insulators published on Physical Review B  90, 161412(R) (2014).

In this paper we predict a magnetoresistance induced by the interfacial Rashba spin orbit coupling in a normal metal/ferromagnetic insulator bilayer system. This new magnetoresistance depends on the angle between current and magnetization directions as the recent discovered "spin Hall magnetoresistance" mechanism caused by a combined action of spin Hall and inverse spin Hall effects. …

Vahram finished his postdoc term

Vahram, from Armenia, joined our group as postdoc fellow in early 2012, and had accomplished several papers on spin quantum dots and spin transport in magnetic thin film structures. Vahram finished his postdoc term in August, and now is awaiting to join Prof. Ke Xia’s group for another postdoc position.

Wish you a successful future!

Paper on spin pumping in antiferromagnet published on PRL

AFM spin pumping

Our paper that predicts significant spin pumping in antiferromagnet has been recently published on Physical Review Letters [link]. 

Spin pumping in ferromagnet is very well known. However, the spin pumping in antiferromagnet is generally believed to be vanishing because of the two compensating sublattices. This simple thinking is actually wrong. In this paper, we argue that the spin pumping from the two compensating sublattice actually constructively enhance each other instead of cancelling. …

Guo Wei, Shi Haosheng, Zhou Lingjun graduated

On May 27, 2014, Guo Wei, Shi Haosheng, and Zhou Lingjun have successfully defended their thesis. All of them will graduate this summer. 

Guo Wei has landed on a physics teaching job at the international sector at Pu Dong Shang De School. Shi Haosheng will continue on his Ph. D. study at North Carolina State University in USA. Zhou Lingjun will pursue his Ph. D. study at University of Manitoba in Canada. 

Paper on spin wave excitation in ferromagnetic insulators published on PRB

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Our paper studying the spin wave excitation in ferromagnetic insulators by a spin Hall current is published on Physical Review B 88, 184403 (2013).

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In this paper, we study a Pt|YIG bilayer structure (see the figure on the right), where a charge current J_c induces a spin Hall current J_stt, which exerts spin-transfer torque on the YIG magnetization, and excites spin waves. In this paper, we developed a self-consistent theory that takes into account the spin diffusion in Pt, and the spin wave dynamics in YIG with the spin pumping and dipole-dipole interaction considered. …

Paper about dynamical spin-spin coupling in quantum dots published on EPL

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Recently Vahram’s paper about dynamical spin-spin coupling of quantum dots is published on Europhysics Letters 104, 17008 (2013).

In this paper, we predict a new type of indirect dynamical spin-spin interaction between two quantum dots that reside in a common electron continuum bath with a rotating magnetic field applied. The two dots are coupled in the following way: spin is pumped to the continuum from one quantum dot due to the rotating field, the pumped spin is then absorbed by the other dot, and vice versa.  …

Mr. Yu Weichao joins our group

Mr. Yu Weichao, graduated from Tongji University, joins our group in 2013 Fall to start his Ph. D. study in spintronics. Mr. Yu is going to work on magnonics simulation.

Welcome to the group!

Paper about spin transport in metallic thin film published on PRB (Rapid)

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Recently, our paper about spin transport in metallic thin film sandwiched by insulators is published on Physical Review B 87, 081407(R) (2013) (Rapid Communications).

In this paper, we predicted theoretically that, when a normal metallic thin film (without bulk spin-orbit coupling, such as Cu or Al) is sandwiched by two insulators (See right figure), two prominent effects arise due to the interfacial spin-orbit coupling: a giant spin-Hall conductivity due to the surface scattering and a transverse electric polarization due to the spin-dependent phase shift in the spinor wave functions.

Paper about spin torque oscillator published on PRB (Rapid)

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Our recent paper about field-free spin torque oscillator using synthetic-ferromagnet is published on Physical Review B 87, 020409(R) (2013) (Rapid Communications).

In this paper, we predict that a ferromagneticaly coupled synthetic-ferromagnet (see the right figure) can be excited into dynamical precessional states by an applied current without external magnetic fields.

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A spin-torque microwave oscillator is a device which can generate microwave frequency signals based on

Paper about spin wave excitation published on PRL

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Our recent paper about the spin wave excitation by spin current in magnetic insulator thin films has been accepted and published on Physical Review Letters (link). 

This paper predicts a new type of surface spin waves (highlighted as in the yellow panels in the picture on the right) induced by the easy-axis surface anisotropy, and the required excitation current is small while the resulting excitation power is large.


Spin Seebeck effect paper published on Nature Materials!

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Our experiment + theory paper on spin Seebeck effect is published on Nature Materials (link), along with another paper on the spin Seebeck effect on ferromagnetic semiconductors.

And the spin Seebeck topic appears on News and Views on Nature Materials issue.


© Jiang Xiao 2014