Introduction of spin torques

2017 ◽  
Author(s):  
T. Kimura
Keyword(s):  
Angular Momentum ◽  
Giant Magnetoresistance ◽  
Spontaneous Magnetization ◽  
Magnetic Domain ◽  
Magnetic Multilayers ◽  
Transfer Effect ◽  
Spin Transfer Torque ◽  
Spin Transfer ◽  
Spin Angular Momentum ◽  
Spin Torques

This chapter discusses the spin-transfer effect, which is described as the transfer of the spin angular momentum between the conduction electrons and the magnetization of the ferromagnet that occurs due to the conservation of the spin angular momentum. L. Berger, who introduced the concept in 1984, considered the exchange interaction between the conduction electron and the localized magnetic moment, and predicted that a magnetic domain wall can be moved by flowing the spin current. The spin-transfer effect was brought into the limelight by the progress in microfabrication techniques and the discovery of the giant magnetoresistance effect in magnetic multilayers. Berger, at the same time, separately studied the spin-transfer torque in a system similar to Slonczewski’s magnetic multilayered system and predicted spontaneous magnetization precession.

scholarly journals Current-induced spin–orbit torques

2011 ◽  
Vol 369 (1948) ◽  
pp. 3175-3197 ◽  
Author(s):  
Pietro Gambardella ◽  
Ioan Mihai Miron
Keyword(s):  
Angular Momentum ◽  
Exchange Coupling ◽  
Spin Transfer Torque ◽  
Spin Transfer ◽  
Spin Torque ◽  
Inversion Symmetry ◽  
Spin Orbit ◽  
Great Flexibility ◽  
Combined Action ◽  
Proper Material

The ability to reverse the magnetization of nanomagnets by current injection has attracted increased attention ever since the spin-transfer torque mechanism was predicted in 1996. In this paper, we review the basic theoretical and experimental arguments supporting a novel current-induced spin torque mechanism taking place in ferromagnetic (FM) materials. This effect, hereafter named spin–orbit (SO) torque, is produced by the flow of an electric current in a crystalline structure lacking inversion symmetry, which transfers orbital angular momentum from the lattice to the spin system owing to the combined action of SO and exchange coupling. SO torques are found to be prominent in both FM metal and semiconducting systems, allowing for great flexibility in adjusting their orientation and magnitude by proper material engineering. Further directions of research in this field are briefly outlined.

Modelling spin transfer torque and magnetoresistance in magnetic multilayers

2007 ◽  
Vol 19 (16) ◽  
pp. 165212 ◽  
Author(s):  
A Manchon ◽  
N Ryzhanova ◽  
N Strelkov ◽  
A Vedyayev ◽  
B Dieny
Keyword(s):  
Magnetic Multilayers ◽  
Spin Transfer Torque ◽  
Spin Transfer

scholarly journals A New Circuit Model for Spin-Torque Oscillator Including Perpendicular Torque of Magnetic Tunnel Junction

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Hyein Lim ◽  
Sora Ahn ◽  
Miryeon Kim ◽  
Seungjun Lee ◽  
Hyungsoon Shin
Keyword(s):  
Tunnel Junction ◽  
Giant Magnetoresistance ◽  
New Technology ◽  
Magnetic Tunnel Junction ◽  
Spin Transfer Torque ◽  
Spin Transfer ◽  
Spin Torque ◽  
Mean Oscillation ◽  
Proposed Model ◽  
Level Model

Spin-torque oscillator (STO) is a promising new technology for the future RF oscillators, which is based on the spin-transfer torque (STT) effect in magnetic multilayered nanostructure. It is expected to provide a larger tunability, smaller size, lower power consumption, and higher level of integration than the semiconductor-based oscillators. In our previous work, a circuit-level model of the giant magnetoresistance (GMR) STO was proposed. In this paper, we present a physics-based circuit-level model of the magnetic tunnel junction (MTJ)-based STO. MTJ-STO model includes the effect of perpendicular torque that has been ignored in the GMR-STO model. The variations of three major characteristics, generation frequency, mean oscillation power, and generation linewidth of an MTJ-STO with respect to the amount of perpendicular torque, are investigated, and the results are applied to our model. The operation of the model was verified by HSPICE simulation, and the results show an excellent agreement with the experimental data. The results also prove that a full circuit-level simulation with MJT-STO devices can be made with our proposed model.

scholarly journals DATA STORAGE: REVIEW OF HEUSLER COMPOUNDS

SPIN ◽  
2012 ◽  
Vol 02 (04) ◽  
pp. 1230006 ◽  
Author(s):  
ZHAOQIANG BAI ◽  
LEI SHEN ◽  
GUCHANG HAN ◽  
YUAN PING FENG
Keyword(s):  
Data Storage ◽  
Giant Magnetoresistance ◽  
Functional Materials ◽  
Recent Decade ◽  
Spin Transfer Torque ◽  
Spin Transfer ◽  
Magnetic Data ◽  
Heusler Compounds ◽  
Storage Devices ◽  
The Family

In the recent decade, the family of Heusler compounds has attracted tremendous scientific and technological interest in the field of spintronics. This is essentially due to their exceptional magnetic properties, which qualify them as promising functional materials in various data-storage devices, such as giant-magnetoresistance spin valves, magnetic tunnel junctions, and spin-transfer torque devices. In this article, we provide a comprehensive review on the applications of the Heusler family in magnetic data storage. In addition to their important roles in the performance improvement of these devices, we also try to point out the challenges as well as possible solutions, of the current Heusler-based devices. We hope that this review would spark further investigation efforts into efficient incorporation of this eminent family of materials into data storage applications by fully arousing their intrinsic potential.

Spin–Orbit Torques in Metallic Magnetic Multilayers: Challenges and New Opportunities

SPIN ◽  
2017 ◽  
Vol 07 (03) ◽  
pp. 1740013 ◽  
Author(s):  
Tao Wang ◽  
John Q. Xiao ◽  
Xin Fan
Keyword(s):  
Giant Magnetoresistance ◽  
Rapid Development ◽  
Measurement Techniques ◽  
Random Access ◽  
Magnetic Multilayers ◽  
Spin Transfer Torque ◽  
Spin Torque ◽  
Great Effort ◽  
Spin Orbit ◽  
Practical Applications

Two decades after the discovery of the giant magnetoresistance that revolutionizes the hard disk drive, the rapid development of spin torque-based magnetic random access memory has once again demonstrated the great potential of spintronics in practical applications. While the industrial application is mainly focusing on the implementation of current-induced spin transfer torque (STT) in magnetic tunnel junctions, a new type of spin torque emerges due to the spin–orbit interaction in magnetic multilayers. A great effort has been devoted by the scientific community to study the so-called spin–orbit torque (SOT), which is not only of interest to fundamental science, but also exhibits potential for the application of current-induced magnetization switching. In this paper, we will review recent development in the SOTs including the fundamental understanding, materials development and measurement techniques. We will also discuss the challenges of using the SOT in potential applications, particularly on the switching of perpendicularly magnetized films.

scholarly journals Revealing angular momentum transfer channels and timescales in the ultrafast demagnetization process of ferromagnetic semiconductors

2019 ◽  
Vol 116 (39) ◽  
pp. 19258-19263
Author(s):  
Zhanghui Chen ◽  
Jun-Wei Luo ◽  
Lin-Wang Wang
Keyword(s):  
Angular Momentum ◽  
Density Functional ◽  
Dominant Role ◽  
Spin Transfer ◽  
Theory Approach ◽  
Spin Angular Momentum ◽  
Spintronic Devices ◽  
Electron Phonon Coupling ◽  
Stage Process

Ultrafast control of magnetic order by light provides a promising realization for spintronic devices beyond Moore’s Law and has stimulated intense research interest in recent years. Yet, despite 2 decades of debates, the key question of how the spin angular momentum flows on the femtosecond timescale remains open. The lack of direct first-principle methods and pictures for such process exacerbates the issue. Here, we unravel the laser-induced demagnetization mechanism of ferromagnetic semiconductor GaMnAs, using an efficient time-dependent density functional theory approach that enables the direct real-time snapshot of the demagnetization process. Our results show a clear spin-transfer trajectory from the localized Mn-d electrons to itinerant carriers within 20 fs, illustrating the dominant role of sp−d interaction. We find that the total spin of localized electrons and itinerant carriers is not conserved in the presence of spin-orbit coupling (SOC). Immediately after laser excitation, a growing percentage of spin-angular momentum is quickly transferred to the electron orbital via SOC in about 1 ps, then slowly to the lattice via electron–phonon coupling in a few picoseconds, responsible for the 2-stage process observed experimentally. The spin-relaxation time via SOC is about 300 fs for itinerant carriers and about 700 fs for Mn-d electrons. These results provide a quantum-mechanical microscopic picture for the long-standing questions regarding the channels and timescales of spin transfer, as well as the roles of different interactions underlying the GaMnAs demagnetization process.

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