Spin orbit effects

  • YIG delay lines:


Microwave wireless telecommunications are the backbone of the information age. They enable the exchange of data between connected objects. The Internet of Things is expected to connect as much as 80 billion objects by 2020. Accommodating such large number of handsets requires a paradigm shift in the performance of microwave analog front-end technology (MAFET). The future revolves around cognitive communication, where smart components are opportunistically allocating communication channels adaptively. But the development of a new cognitive-MAFET is limited by the standard trade-off between selectivity and agility 2 interdependent quantities linked by the damping coefficient. Our aim is to overcome this by developing novel microwave garnet functions with tunable loss  by focusing upon the outstanding ultra-low damping properties of YIG. The main deliverable of the project is to fabricate a traveling spin-wave delay line, whose delay time is increased beyond the natural spin-wave decay, which presently limits this technology.








FIG : The YIG delay line with tunable loss. SWs are excited under the left RF input antenna (gray). They propagate along the YIG (green), patterned as a magnonic crystal (anti-dot array shown as black holes) that acts as a λ/2 reflection grating. An electrode with strong spin-orbit interaction, made of Pt (yellow), is deposited on top for signal amplification by stimulated emission. SWs are converted back to an electromagnetic signal at the right output antenna after an extended delay. Interference between variable delays allows for a precise frequency filtering.

The innovative objective of this project is to extend to the microwave frequency range the concept of doped transmission used by optical telecommunication. A first aim is to develop a loss-compensated spin-wave propagation medium. A second aim is to pattern this medium into a micron-size wave guide in order to achieve an analog delay line of unprecedented quality and integrable into the future electronics. The core idea is to join a magnetic insulator and a normal metal. In such a double-layered structure the magnetic insulator – Yttrium-Iron Garnet (YIG) – provides a low-loss propagation medium where an input microwave electromagnetic signal is converted into a slowly propagating spin-wave. A key property is that intrinsic losses of the traveling spin-wave are partially or even fully compensated allowing the delay time to be increased beyond the natural spin-wave decay, which presently is a key issue that limits this technology. The oscillatory signal will be amplified by an injected flow of angular momentum (or pure spin current) from an out-of-equilibrium spin accumulation layer produced by the electrons moving in an adjacent metallic layer. The spin current will be created by the spin-Hall effect (requires strong spin-orbit metals or alloys: e.g. Pt, Ta or CuIr and AuW). The net result of the spin current will be to amplify (or to reduce, depending on the sign of the applied current) the propagating signal by the process of stimulated emission at the metal/insulator interface. Delays of few microseconds could then be potentially achieved over micrometer distances. In the future, such delay line could be used as the elementary building block for other high performance microwave devices such as an ultra-low phase noise oscillator or a voltage controlled tunable filter. Target applications lie in radar and telecommunication technology, which are looking for electronically tuned ultra-narrow band, non-reciprocal devices, combining both high-agility and ultra-narrow selectivity.


  • YIG tuned oscillators:


Up to now, the majority of commercially available YIG Tuned Oscillators (YTO) use a millimetric size YIG sphere perfectly polished. We plan to replace them by micro-structured YIG devices  patterned out from ultra-thin YIG films fabricated by Liquid Phase Epitaxy.  Miniature YTO, whose scope would be new sources of very high RF performance with low power consumption for mobile or embedded applications in the field of radar or telecommunications. Our objective is to incorporate a YIG film micro-structured in a miniature electromagnet (approx. 1cm size) with a active circuit to make it self-oscillate.


The project aims at developing miniature high frequency oscillators with outstanding specifications : ultra-high frequency selectivity, tunability over several octaves, energy efficiency, ultra-low phase noise and very stable output. To reach this target, we will capitalize on our progress realized in the growth of YIG thin films having very low losses. The originality is to fabricate a YIG tuned oscillator (YTO) based on a resonating YIG planar microstructure obtained by lithography of a thin film. Thanks to scale effects expected through reducing the size of the component, it becomes possible to tune its frequency over 4 octaves by using a miniature electromagnet which will consume less than 100 mW and/or by using permanent magnets displaced by a piezo-electric actuator. Technological applications lie in embedded wide band electronics for radar and wireless communication, with fallout for defense in electronic war by developing new components for counter-measurement and spectral analysis, and civil fallout in cognitive telecommunication with sweep generators and frequency synthesizers.  The second objective is to lift the technological barrier concerning the figure of merit of an analog oscillator, which is limited by the trade-off between selectivity and agility. Both quantities are indeed interdependent, since they are related through the damping parameter of the component. Thanks to a recently discovered physical effect, which has been deeply studied within the ANR ASTRID Trinidad project, it becomes possible to integrate a new functionality to the YTO. It is to use spin-orbit effects in a metallic layer adjacent to the YIG by injecting an electrical current in order to tune the quality factor in a few tens of nanoseconds. Implementing this functionality in YTO would be a technological breakthrough as it would solve the dichotomy between agility and selectivity

Olivier Klein (SPINTEC), Ursula Ebels (SPINTEC), Liliana Prejbeanu (Simulation), Daria Gusakova (Simulation),  Laurent Vila (SP2M), Mairbek Chschiev (SPINTEC)


Figure 1



Patent US 20070247243: Microwave Oscillator Tuned With a Ferromagnetic Thin Film (O. Klein and V.V. Naletov)



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