Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms

Antiferromagnetic materials could represent the future of spintronic applications thanks to the numerous interesting features they combine: they are robust against perturbation due to magnetic fields, produce no stray fields, display ultrafast dynamics and are capable of generating large magneto-transport effects Intense research efforts over the past decade have been invested in unraveling spin transport properties in antiferromagnetic materials Whether spin transport can be used to drive the antiferromagnetic order and how subsequent variations can be detected are some of the thrilling challenges currently being addressed Antiferromagnetic spintronics started out with studies on spin transfer, and has undergone a definite revival in the last few years with the publication of pioneering articles on the use of spin-orbit interactions in antiferromagnets This paradigm shift offers possibilities for radically new concepts for spin manipulation in electronics Central to these endeavors are the need for predictive models, relevant disruptive materials and new experimental designs This paper reviews the most prominent spintronic effects described based on theoretical and experimental analysis of antiferromagnetic materials It also details some of the remaining bottlenecks and suggests possible avenues for future research

Antiferromagnetic spintronics

There are two kinds of tutorial articles: those that provide a primer on an established topic and those that let us in on the ground floor of something of emerging importance. The first type of tutorial can have a noted expert who has been gracious (and brave) enough to write a field guide about a particular topic. The other sort of tutorial typically involves researchers who have each been laboring on a topic for some years. Both sorts of tutorial articles are very much desired. But we, as an editorial board for both Systems and Transactions, know that there has been no logical place for them in the AESS until this series was started several years ago. With these tutorials, we hope to continue to give them a home, a welcome, and provide a service to our membership. We do not intend to publish tutorials on a regular basis, but we hope to deliver them once or twice per year. We need and welcome good, useful tutorial articles (both kinds) in relevant AESS areas. If you, the reader, can offer a topic of interest and an author to write about it, please contact us. Self-nominations are welcome, and even more ideal is a suggestion of an article that the editor(s) can solicit. All articles will be reviewed in detail. Criteria on which they will be judged include their clarity of presentation, relevance, and likely audience, and, of course, their correctness and scientific merit. As to the mathematical level, the articles in this issue are a good guide: in each case the author has striven to explain complicated topics in simple-well, tutorial-terms. There should be no (or very little) novel material: the home for archival science is the Transactions Magazine, and submissions that need to be properly peer reviewed would be rerouted there. Likewise, articles that are interesting and descriptive, but lack significant tutorial content, ought more properly be submitted to the Systems Magazine.

What is a tutorial

Spin Hall effects convert charge currents into spin currents and vice versa even in nonmagnetic conductors due to spin orbit coupling. This enables spin Hall effects to be utilized both for the generation and detection of spin currents and magnetization dynamics. This paper reviews the experimental characterization of these effects in metallic systems, which have so far shown the highest efficiency in using spin Hall effects for charge-to-spin interconversion. The advantages and disadvantages of complimentary measurement techniques are discussed and in addition an outlook of the possible impact on applications is presented.

Spin Hall Effects in Metals

A M was supported by the King Abdullah University of Science and Technology (KAUST) T J acknowledges support from the EU FET Open RIA Grant No 766566, the Ministry of Education of the Czech Republic Grant No LM2015087 and LNSM-LNSpin, and the Grant Agency of the Czech Republic Grant No 19-28375X J S acknowledges the Alexander von Humboldt Foundation, EU FET Open Grant No 766566, EU ERC Synergy Grant No 610115, and the Transregional Collaborative Research Center (SFB/TRR) 173 SPIN+X K G and P G acknowledge stimulating discussions with C O Avci and financial support by the Swiss National Science Foundation (Grants No 200021-153404 and No 200020-172775) and the European Commission under the Seventh Framework Program (spOt project, Grant No 318144) A T acknowledges support by the Agence Nationale de la Recherche, Project No ANR-17-CE24-0025 (TopSky) J Ž acknowledges the Grant Agency of the Czech Republic Grant No 19-18623Y and support from the Institute of Physics of the Czech Academy of Sciences and the Max Planck Society through the Max Planck Partner Group programme

/pdf/current-induced-spin-orbit-torques-in-ferromagnetic-and-3tdt106r3u.pdf

Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems

We demonstrate that the lowest threshold of spin-wave excitation in an in-plane magnetized magnetic nanocontact driven by spin-polarized current is achieved for a nonlinear self-localized spin-wave mode-standing spin-wave bullet--stabilized by current-induced nonlinear dissipation. This nonlinear mode has a nonpropagating evanescent character, is localized in the region comparable with the contact radius, and has a frequency that is lower than the frequency of the linear ferromagnetic resonance. The threshold current and generated frequency at the threshold theoretically calculated for this mode are in quantitative agreement with experiment.

Spin wave mode excited by spin-polarized current in a magnetic nanocontact is a standing self-localized wave bullet.

The time reversal of pulsed signals or propagating wave packets has long been recognized to have profound scientific and technological significance. Until now, all experimentally verified time-reversal mechanisms have been reliant upon nonlinear phenomena such as four-wave mixing. In this paper, we report the experimental realization of all-linear time reversal. The time-reversal mechanism we propose is based on the dynamic control of an artificial crystal structure, and is demonstrated in a spin-wave system using a dynamic magnonic crystal. The crystal is switched from an homogeneous state to one in which its properties vary with spatial period a, while a propagating wave packet is inside. As a result, a linear coupling between wave components with wave vectors k≈π/a and k′=k−2ππ/a≈−π/a is produced, which leads to spectral inversion, and thus to the formation of a time-reversed wave packet. The reversal mechanism is entirely general and so applicable to artificial crystal systems of any physical nature.

/pdf/all-linear-time-reversal-by-a-dynamic-artificial-crystal-1ncc4bx1qy.pdf

All-linear time reversal by a dynamic artificial crystal

It is shown that the generation linewidth of an auto-oscillator with a nonlinear frequency shift (i.e., an auto-oscillator in which frequency depends on the oscillation amplitude) is substantially larger than the linewidth of a conventional quasilinear auto-oscillator due to the renormalization of the phase noise caused by the nonlinearity of the oscillation frequency. The developed theory, when applied to a spin-torque auto-oscillator, gives a good description of experimentally measured angular and temperature dependences of the linewidth.

https://arxiv.org/pdf/cond-mat/0703317.pdf

Generation linewidth of an auto-oscillator with a nonlinear frequency shift: spin-torque nano-oscillator.

We experimentally demonstrate a series of fractional synchronization regimes (Devil's staircase) in a spin-torque nano-oscillator driven by a microwave field. These regimes are characterized by rational relations between the driving frequency and the frequency of the oscillation. An analysis based on the phase model of auto-oscillator indicates that fractional synchronization becomes possible when the driving signal breaks the symmetry of the oscillation, while the synchronization ranges are determined by the geometry of the oscillation orbit. Measurements of fractional synchronization can be utilized to obtain information about the oscillation characteristics in nanoscale systems not accessible to direct imaging techniques.

/pdf/fractional-synchronization-of-spin-torque-nano-oscillators-4yij8ngyjn.pdf

Fractional synchronization of spin-torque nano-oscillators.

Control of spin waves in a ferrite thin film via interfacial spin scattering was demonstrated. The experiments used a 4.6  μm-thick yttrium iron garnet (YIG) film strip with a 20-nm thick Pt capping layer. A dc current pulse was applied to the Pt layer and produced a spin current across the Pt thickness. As the spin current scatters off the YIG surface, it can either amplify or attenuate spin-wave pulses that travel in the YIG strip, depending on the current or field configuration. The spin scattering also affects the saturation behavior of high-power spin waves.

/pdf/control-of-spin-waves-in-a-thin-film-ferromagnetic-insulator-3kbks9bfr7.pdf

Vasil Tiberkevich

Papers

Spin wave mode excited by spin-polarized current in a magnetic nanocontact is a standing self-localized wave bullet.

All-linear time reversal by a dynamic artificial crystal

Generation linewidth of an auto-oscillator with a nonlinear frequency shift: spin-torque nano-oscillator.

Fractional synchronization of spin-torque nano-oscillators.

Control of spin waves in a thin film ferromagnetic insulator through interfacial spin scattering.