Proceedings

EPJ B Highlight - Spinning towards robust microwave generation on the nano scale

Snapshots of an ensemble of 100 spin-torque oscillators at different points in time, plotting values of inductance (L) against capacitance (C). Red dots show individual oscillators.

New study explains why it is not possible to couple nano-scale microwave generators known as spin-torque oscillators together in series to generate a macroscopic strength signal

Spin-torque oscillators (STOs) are nanoscale devices that generate microwaves using changes in magnetic field direction, but those produced by any individual device are too weak for practical applications. Physicists have attempted - and, to date, consistently failed - to produce reliable microwave fields by coupling large ensembles. Michael Zaks from Humboldt University of Berlin and Arkady Pikovsky from the University of Potsdam in Germany have now shown why connecting these devices in series cannot succeed, and, at the same time, suggested other paths to explore. Their work was recently published in EPJ B.

The physics behind spin-torque oscillations is the same as that behind the hard disk drive of the computer on which you are very likely reading this text. It is a quantum mechanical effect known as 'giant magnetoresistance', in which changing the external magnetic field around a stack of layers of alternating ferromagnetic and non-magnetic metals gives rise to substantial changes in electrical resistance.

If the electric force produced is strong enough and the magnetic layers are free to rotate, magnetic oscillation occurs and microwaves are generated; this is the STO effect. However, only synchronised oscillations from large ensembles of oscillators can produce microwaves that are sufficiently powerful to be useful. Zaks and Pikovsky's work illustrates why it has proven so difficult to synchronise them.

To do so, the physicists simulated the motion of an ensemble of serially coupled STOs using the equations of non-linear dynamics. Their analysis revealed that the ensembles were always too unstable for the oscillations to remain coherent. In particular, they found that the random fluctuations of electric current that affect all oscillators simultaneously - so-called 'common noise' - do not stabilise the oscillations, as some had predicted. Instead, in some cases, sufficiently strong fluctuations were able to suppress the oscillations altogether.

Zaks and Pikovsky have dubbed this newly discovered phenomenon 'noise-induced oscillation death'. Armed with new theoretical knowledge on this system, they are now investigating other methods for coupling these nanoscale machines to produce robust microwaves on the macro scale.

This was our first experience of publishing with EPJ Web of Conferences. We contacted the publisher in the middle of September, just one month prior to the Conference, but everything went through smoothly. We have had published MNPS Proceedings with different publishers in the past, and would like to tell that the EPJ Web of Conferences team was probably the best, very quick, helpful and interactive. Typically, we were getting responses from EPJ Web of Conferences team within less than an hour and have had help at every production stage.
We are very thankful to Solange Guenot, Web of Conferences Publishing Editor, and Isabelle Houlbert, Web of Conferences Production Editor, for their support. These ladies are top-level professionals, who made a great contribution to the success of this issue. We are fully satisfied with the publication of the Conference Proceedings and are looking forward to further cooperation. The publication was very fast, easy and of high quality. My colleagues and I strongly recommend EPJ Web of Conferences to anyone, who is interested in quick high-quality publication of conference proceedings.

On behalf of the Organizing and Program Committees and Editorial Team of MNPS-2019, Dr. Alexey B. Nadykto, Moscow State Technological University “STANKIN”, Moscow, Russia. EPJ Web of Conferences vol. 224 (2019)

ISSN: 2100-014X (Electronic Edition)

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