MASTER

Microwave Amplification by Spin Transfer Emission Radiation

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 Obiettivo del progetto (Objective)

'The intended aim of this project is to explore the application potential of novel Spin-Transfer Oscillators (STO) as tunable and ultra-narrow band microwave radiation sources for mobile and wireless telecommunication technology. The main technological interest of STO devices, which correspond to nano-structured magnetic multilayer pumped by a spin-polarized electrical current and emitting microwave radiation, is their compatibility with monolithic integration. Our proposal specifically addresses the bottleneck issue of power conversion efficiency between dc current pumping and microwave emission of radiation. We propose to take advantage of the phase-locking mechanisms between coupled oscillators to increase significantly the device performance. Our primary objective is to engineer large arrays of coherently coupled oscillators. To achieve this goal, we shall investigate in detail 4 different types of coupling mechanism between neighboring oscillators which may induce phase-locking of the ensemble: 1) coupling through the self-generated microwave current, 2) coupling through the dipolar magnetic field, 3) coupling through the spin-diffusion of the conduction electrons, 4) coupling mediated by spin-waves. Achieving phase-locking between neighboring oscillators also requires substantial progress in our understanding of the fundamental mechanisms that are involved during momentum-transfer from spin-polarized current to the magnetic moments. Our secondary objective is to address both experimentally and theoretically 3 knowledge gaps: identifying (spatio-temporal profile and relaxation times) the fundamental spin-wave eigen-modes excited by a dc current in nano-structured magnetic heterojunctions; understanding the fundamental mechanism underlying non-local effects associated with the diffusion of spin-polarized electrons and its action on the dynamics of the whole system; investigating the magnetization dynamics of a nano-structure in the non-linear regime.'

Introduzione (Teaser)

The demand for smart devices is leading to an increasing downsizing of electronic circuits. EU-funded scientists studied novel nano-oscillators instead of conventional oscillators to overcome the barrier of miniaturisation.

Descrizione progetto (Article)

The generation of oscillations over the microwave frequency range is one of the most important applications of spintronic devices. Such devices exploit electron spin as well as their charge, thus overcoming the increasing limitations of conventional electronics. Of particular interest to wireless communications are spin-transfer nano-oscillators (STNOs).

Scientists initiated the EU-funded project http://iramis.cea.fr/spec/Phocea/Page/index.php?id=23 (MASTER) (Microwave amplification by spin transfer emission radiation) to explore the potential of STNOs for use as tunable and ultra-narrow band microwave radiation sources for mobile and wireless telecommunication technology. The focus was on addressing existing challenges related to insufficient power, too much (phase) noise and narrow frequency ranges.

Taking advantage of large arrays of coherently coupled oscillators (oscillating together at the same frequency), scientists sought to significantly increase device performance. To optimise results, they studied four different mechanisms of coupling between neighbouring oscillators.

Project research resulted in identification of the optimal configuration of N oscillators for synchronisation. Through coupling the magnetisation motion of the two layers that constitute an STNO, scientists achieved the targeted power output and linewidth. They reported enhanced performance up to N=4. The performance characteristics of the optimised array were studied both theoretically and experimentally.

The project developed innovative spin-wave spectroscopic techniques that can excite and detect the magnetisation dynamics of individual STNO independently of spin-transfer effects. These techniques were fundamental to understanding the basic mechanisms involved in spin momentum transfer.

Another achievement was the development a high-performance solver for performing micromagnetic simulations on a very large array of coherently coupled STNOs. In addition, the project created a simple theoretical framework for transport in magnetic multilayers.

SNTOs can cover a different range of frequencies, are easy to fabricate and are compatible with conventional silicon complementary metal-oxide semiconductor technology. These nano-oscillators may soon replace conventional voltage-controlled oscillators that are used in resonant circuits. Another spintronic microwave system could be a dynamic magnetic read head in data storage. A wideband instantaneous frequency detector in the low- and high-frequency ranges for cognitive radio or radar systems is yet another beneficiary of SNTO technology.