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Spin transfer dynamics in nano-oscillators: from the detection of RF signals to the harvesting and t

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General information

Reference : UMR137-VINCRO-003
Workplace : PALAISEAU
Date of publication : Tuesday, February 05, 2019
Scientific Responsible name : Vincent Cros
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 April 2019
Proportion of work : Full time
Remuneration : 1 768,55 € gross monthly

Description of the thesis topic

Spin transfer oscillators are spintronic devices (typically magnetic tunnel junctions) in which the strong coupling between a spin current and a magnetization can be used to generate the excitation of magnetic dynamic modes. A major research effort has recently been made to evaluate the possibility of using the RF current emitted by a STNO to develop new types of nano-RF oscillators. During this PhD, we focus on another aspect of spin transfer that allows to generate a dc voltage by a rectification effect (called spin diode) when an STNO is subjected to a rf current whose frequency corresponds to one of the magnetic resonance modes of the system. We have recently been able to highlight in vortex oscillators not only these spin diode effects but also the resonant expulsion of the vortex core. These two effects are observed for a vortex frequency range between 100 MHz and 1 GHz, but we can also observe them at 2.5 and 5 GHz.
The ambition of the thesis will be to study the potential of using spin diode mechanism and vortex core expulsion for harvesting and transmission of energy in the radio frequency range. We will be interested in the response of a system comprising two nano-oscillators electrically connected when they are subjected to an RF signal in the case where one of the oscillators is in the spin diode regime and the other in the vortex expulsion regime. The objective will be to show that we can recover energy transported by radiofrequency (RF) waves of low power for example in the WI-FI frequency range (around 2.4 GHz or 5 GHz). The device relies on the resonant excitation of magnetic modes (each in a specific frequency range) by spin transfer, which is then converted into voltage. Fundamentally, even though the two effects, ie spin diode and vortex expulsion, have been observed on several vortex-based STNOs, many questions remain open especially on the mechanisms of expulsion / renucleation and their time scales. associates. From a more application point of view, one of the objectives will be to increase the number of electrically connected STNOs devices to form networks in order to improve the output level (dc) but also the sensitivity to very weak RF signals. To test this new feature, one of the goals will be to connect our energy recovery system to an object requiring a battery, such as a sensor, to show the effectiveness of the system and compare it with competing technologies.

The main ambition of the thesis will be to study the potential of using spin diode mechanism and vortex core expulsion for harvesting and transmission of energy in the radio frequency range. We will be interested in the response of a system comprising two nano-oscillators electrically connected when they are subjected to an RF signal in the case where one of the oscillators is in the spin diode regime and the other in the vortex expulsion regime. The objective will be to show that we can recover energy transported by radiofrequency (RF) waves of low power for example in the WI-FI frequency range (around 2.4 GHz or 5 GHz). The device relies on the resonant excitation of magnetic modes (each in a specific frequency range) by spin transfer, which is then converted into voltage. Fundamentally, even though the two effects, ie spin diode and vortex expulsion, have been observed on several vortex-based STNOs, many questions remain open especially on the mechanisms of expulsion / renucleation and their time scales. associates. From a more application point of view, one of the objectives will be to increase the number of electrically connected STNOs devices to form networks in order to improve the output level (dc) but also the sensitivity to very weak RF signals. To test this new feature, one of the goals will be to connect our energy recovery system to an object requiring a battery, such as a sensor, to show the effectiveness of the system and compare it with competing technologies.

The thesis will consist mainly of the characterization of the vortex-based MTJ-STNOs response to field excitation or rf current in both the frequency domain and the time regime. These characterizations will be done by magneto-transport measurements as a function of a dc / rf current. These techniques are accessible to the laboratory. The experimental results will be compared with micromagnetic simulations, also supported by the candidate. Regarding the more application aspect, the canditat (e) will participate, with the team of the laboratory and their external collaborators, in the design of the circuits.

Work Context

This PhD thesis work done at the CNRS / Thales joint lab will be part of a collaborative project with the SPINTEC laboratory, the CEA-LETI located in Grenoble.

Constraints and risks

none

Additional Information

La thèse s'inscrit dans un projet ANR qui a demmaré au 1er décembre 2018 et doit donc démarrer au plus vite.

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