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Suggested and implemented in 1964 by R.C. Jaklevic, J. Lambe, A.H. Silver and J. E. Mercereau, Direct Current Superconducting QUantum Interference Devices (DC SQUIDs) are magnetic flux-to-voltage converters that offer an unequalled sensitivity in magnetic field measurement, being able to detect fields amplitude down to 1E-17 T. This exceptional sensitivity coupled to their high frequency operating rate and reduced noise, makes DC SQUIDs the ideal sensors for a broad range of applications including magnetic resonance analysis, microscopic imaging techniques, cosmology, biomagnetic, magnetotellurics and interferometry. 
However, SQUID magnetometers' most sensitive domains of applications – e.g. spintronics – require for the devices' size to shrink down to the nanometer scale, where numerous challenges remain in terms of noise, sensitivity and nanofabrication techniques. In this context, we propose electromigration as a robust, simple and scalable tool to tailor SQUIDs' junctions down to a few nanometers in order to improve their performances. We demonstrate in the present work the power of the technique to induce modifications in devices consisting of one to three junctions in parallel. In addition, we introduce a simulation-based study which aims to provide new insights into the electromigration process by computing the device's modifications step-by-step, which allows us to improve our comprehension on the local effects of electromigration.

Physique, chimie, mathématiques & sciences de la terre > Physique

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According to the current version of Moore's law, the performance of modern computers is expected to double every 1.5 years. However, as the miniaturization of the transistor components approaches the ultimate size of a few atoms, the exponential trend is expected to flatten by 2025. Recent years have seen the rise of numerous new promising technologies able to enhance even more the performances of modern computing. Among them, spintronics combines the functionalities of usual logic operations as well as data storage under the form of discrete electron spin states. Recent works have shown the possibility to generate microwave frequency oscillations in ferromagnetic systems by pure spin current injection, to achieve magnetization reversal in magnetic spin valves through pure spin currents, and to create memory devices based on current-stimulated migration of domain walls as well as devices powered by the radio frequency waves used in the domain of telecommunications, etc. All these applications require that spin currents can survive over the longest distances possible and that interfaces between different materials composing the devices can be as transparent as possible. Recent works have suggested the possibility to improve the interface quality by local Joule annealing. In this thesis, we lay the foundations at ULiège for the quantitative characterization of spin current injection and diffusion through interfaces between a ferromagnetic and a heavy metal layer. The objectives of this thesis are (i) to measure effects of modulation of damping via spin injection and to electrically detect the spin pumping, (ii) to obtain characteristic physical quantities proper to the device, such as the spin Hall angle and the spin mixing conductance and (iii) to explore the effects of local Joule annealing on the interface between bilayers of Py/Ta and on the magnetic properties of the former. In that perspective, cavity-based and broadband ferromagnetic resonance spectroscopy techniques were optimized for these specific applications.

Spintronics --- Spin pumping --- Modulation of damping --- Ferromagnetic resonance --- Joule annealing --- Physique, chimie, mathématiques & sciences de la terre > Physique