Multilayer spintronic neural networks with radio-frequency connections

Spintronic nano-synapses and nano-neurons perform complex cognitive computations with high accuracy thanks to their rich, reproducible and controllable magnetization dynamics. These dynamical nanodevices could transform artificial intelligence hardware, provided that they implement state-of-the art deep neural networks. However, there is today no scalable way to connect them in multilayers. Here we show that the flagship nano-components of spintronics, magnetic tunnel junctions, can be connected into multilayer neural networks where they implement both synapses and neurons thanks to their magnetization dynamics, and communicate by processing, transmitting and receiving radio frequency (RF) signals. We build a hardware spintronic neural network composed of nine magnetic tunnel junctions connected in two layers, and show that it natively classifies nonlinearly-separable RF inputs with an accuracy of 97.7%. Using physical simulations, we demonstrate that a large network of nanoscale junctions can achieve state-of the-art identification of drones from their RF transmissions, without digitization, and consuming only a few milliwatts, which is a gain of more than four orders of magnitude in power consumption compared to currently used techniques. This study lays the foundation for deep, dynamical, spintronic neural networks

The seeds of divergence: the economy of French North America, 1688 to 1760

Generally, Canada has been ignored in the literature on the colonial origins of divergence with most of the attention going to the United States. Late nineteenth century estimates of income per capita show that Canada was relatively poorer than the United States and that within Canada, the French and Catholic population of Quebec was considerably poorer. Was this gap long standing? Some evidence has been advanced for earlier periods, but it is quite limited and not well-suited for comparison with other societies. This thesis aims to contribute both to Canadian economic history and to comparative work on inequality across nations during the early modern period. With the use of novel prices and wages from Quebec—which was then the largest settlement in Canada and under French rule—a price index, a series of real wages and a measurement of Gross Domestic Product (GDP) are constructed. They are used to shed light both on the course of economic development until the French were defeated by the British in 1760 and on standards of living in that colony relative to the mother country, France, as well as the American colonies. The work is divided into three components. The first component relates to the construction of a price index. The absence of such an index has been a thorn in the side of Canadian historians as it has limited the ability of historians to obtain real values of wages, output and living standards. This index shows that prices did not follow any trend and remained at a stable level. However, there were episodes of wide swings—mostly due to wars and the monetary experiment of playing card money. The creation of this index lays the foundation of the next component. The second component constructs a standardized real wage series in the form of welfare ratios (a consumption basket divided by nominal wage rate multiplied by length of work year) to compare Canada with France, England and Colonial America. Two measures are derived. The first relies on a “bare bones” definition of consumption with a large share of land-intensive goods. This measure indicates that Canada was poorer than England and Colonial America and not appreciably richer than France. However, this measure overestimates the relative position of Canada to the Old World because of the strong presence of land-intensive goods. A second measure is created using a “respectable” definition of consumption in which the basket includes a larger share of manufactured goods and capital-intensive goods. This second basket better reflects differences in living standards since the abundance of land in Canada (and Colonial America) made it easy to achieve bare subsistence, but the scarcity of capital and skilled labor made the consumption of luxuries and manufactured goods (clothing, lighting, imported goods) highly expensive. With this measure, the advantage of New France over France evaporates and turns slightly negative. In comparison with Britain and Colonial America, the gap widens appreciably. This element is the most important for future research. By showing a reversal because of a shift to a different type of basket, it shows that Old World and New World comparisons are very sensitive to how we measure the cost of living. Furthermore, there are no sustained improvements in living standards over the period regardless of the measure used. Gaps in living standards observed later in the nineteenth century existed as far back as the seventeenth century. In a wider American perspective that includes the Spanish colonies, Canada fares better. The third component computes a new series for Gross Domestic Product (GDP). This is to avoid problems associated with using real wages in the form of welfare ratios which assume a constant labor supply. This assumption is hard to defend in the case of Colonial Canada as there were many signs of increasing industriousness during the eighteenth and nineteenth centuries. The GDP series suggest no long-run trend in living standards (from 1688 to circa 1765). The long peace era of 1713 to 1740 was marked by modest economic growth which offset a steady decline that had started in 1688, but by 1760 (as a result of constant warfare) living standards had sunk below their 1688 levels. These developments are accompanied by observations that suggest that other indicators of living standard declined. The flat-lining of incomes is accompanied by substantial increases in the amount of time worked, rising mortality and rising infant mortality. In addition, comparisons of incomes with the American colonies confirm the results obtained with wages— Canada was considerably poorer. At the end, a long conclusion is provides an exploratory discussion of why Canada would have diverged early on. In structural terms, it is argued that the French colony was plagued by the problem of a small population which prohibited the existence of scale effects. In combination with the fact that it was dispersed throughout the territory, the small population of New France limited the scope for specialization and economies of scale. However, this problem was in part created, and in part aggravated, by institutional factors like seigneurial tenure. The colonial origins of French America’s divergence from the rest of North America are thus partly institutional

Modeling of domain walls dynamics in circular cross-section nanowires

Cette thèse présente une étude théorique de la dynamique de parois de domaines magnétiques sous courant dans des nanofils magnétiques doux à section circulaire. Ce travail se focalise sur des phénomènes critiques, tels que le piégeage de parois et le changement de leur structure interne. Nous combinons des simulations micromagnétiques avec des descriptions analytiques simplifiées afin de fournir une vue d'ensemble des paramètres clés de cette étude, utiles à la prédiction et à la compréhension des expériences. En particulier, le manuscrit quantifie deux phénomènes critiques. Premièrement, nous nous sommes intéressés au contrôle de la position des parois de domaines. Il peut être exercé à l'aide de modulations de diamètre, créant une barrière de potentiel s'opposant à la propagation, et donc nécessitant un courant de seuil pour la franchir. Pour cela, un modèle analytique a été développé pour des fils de diamètres modérés ( 7 lex) dont les effets avaient été négligés jusqu’à présent. Dans ces géométries, la paroi Point-de-Bloch est la plus favorable des textures magnétiques. L’amplitude du champ Oersted est considérable, jouant un rôle majeur dans la stabilisation de paroi pour la dynamique ultra-rapide. Tout particulièrement, le manuscrit quantifie le phénomène de la sélection de circulation de Point-de-Bloch observé expérimentalement dans un travail récent, avec un accord quantitatif sur le courant de seuil. Les simulations micromagnétiques ont aussi mis en évidence la complexité des transformations de la paroi point-de-Bloch.In this thesis is presented a micromagnetic study of current-driven domain wall (DW) dynamics in soft magnetic nanowires with a circular cross section. This work is focused on critical phenomena, such as DW pinning and modifications in their internal structure. Micromagnetic simulations were combined with simplified analytical descriptions to provide an overview of the several key parameters, crucial for predicting and understanding experiments. The precise control of the position of the DWs may be achieved through modulations of the diameter of the nanowires, giving rise to a potential barrier acting against propagation, and thus, requiring a threshold current to be overcome. An analytical model was developed for moderate diameter wires ( 7 lex), the effects of the Oersted field generated by the applied current, which had been overlooked so far, are considered. In such geometries, the Bloch-point wall (BPW) is the most stable magnetic texture, and as such, the most favored one. The considerable amplitude of the Oesterd field plays a major role in the stabilization of the DW in the ultra-fast dynamic. In particular, this work aimed to quantify the Bloch-point circulation selection phenomenon, observed and described in one of our recent experimental works, with a quantitative theoretical agreement on the value of the threshold current. The micromagnetic simulations have also highlighted the intrinsic complexity of the Bloch-point wall transformations

Modélisation de la dynamique de parois de domaines dans des nanofils à section circulaire

In this thesis is presented a micromagnetic study of current-driven domain wall (DW) dynamics in soft magnetic nanowires with a circular cross section. This work is focused on critical phenomena, such as DW pinning and modifications in their internal structure. Micromagnetic simulations were combined with simplified analytical descriptions to provide an overview of the several key parameters, crucial for predicting and understanding experiments. The precise control of the position of the DWs may be achieved through modulations of the diameter of the nanowires, giving rise to a potential barrier acting against propagation, and thus, requiring a threshold current to be overcome. An analytical model was developed for moderate diameter wires ( 7 lex), the effects of the Oersted field generated by the applied current, which had been overlooked so far, are considered. In such geometries, the Bloch-point wall (BPW) is the most stable magnetic texture, and as such, the most favored one. The considerable amplitude of the Oesterd field plays a major role in the stabilization of the DW in the ultra-fast dynamic. In particular, this work aimed to quantify the Bloch-point circulation selection phenomenon, observed and described in one of our recent experimental works, with a quantitative theoretical agreement on the value of the threshold current. The micromagnetic simulations have also highlighted the intrinsic complexity of the Bloch-point wall transformations.Cette thèse présente une étude théorique de la dynamique de parois de domaines magnétiques sous courant dans des nanofils magnétiques doux à section circulaire. Ce travail se focalise sur des phénomènes critiques, tels que le piégeage de parois et le changement de leur structure interne. Nous combinons des simulations micromagnétiques avec des descriptions analytiques simplifiées afin de fournir une vue d'ensemble des paramètres clés de cette étude, utiles à la prédiction et à la compréhension des expériences. En particulier, le manuscrit quantifie deux phénomènes critiques. Premièrement, nous nous sommes intéressés au contrôle de la position des parois de domaines. Il peut être exercé à l'aide de modulations de diamètre, créant une barrière de potentiel s'opposant à la propagation, et donc nécessitant un courant de seuil pour la franchir. Pour cela, un modèle analytique a été développé pour des fils de diamètres modérés ( 7 lex) dont les effets avaient été négligés jusqu’à présent. Dans ces géométries, la paroi Point-de-Bloch est la plus favorable des textures magnétiques. L’amplitude du champ Oersted est considérable, jouant un rôle majeur dans la stabilisation de paroi pour la dynamique ultra-rapide. Tout particulièrement, le manuscrit quantifie le phénomène de la sélection de circulation de Point-de-Bloch observé expérimentalement dans un travail récent, avec un accord quantitatif sur le courant de seuil. Les simulations micromagnétiques ont aussi mis en évidence la complexité des transformations de la paroi point-de-Bloch

Modélisation de la dynamique de parois de domaines dans des nanofils à section circulaire

In this thesis is presented a micromagnetic study of current-driven domain wall (DW) dynamics in soft magnetic nanowires with a circular cross section. This work is focused on critical phenomena, such as DW pinning and modifications in their internal structure. Micromagnetic simulations were combined with simplified analytical descriptions to provide an overview of the several key parameters, crucial for predicting and understanding experiments. The precise control of the position of the DWs may be achieved through modulations of the diameter of the nanowires, giving rise to a potential barrier acting against propagation, and thus, requiring a threshold current to be overcome. An analytical model was developed for moderate diameter wires ( 7 lex), the effects of the Oersted field generated by the applied current, which had been overlooked so far, are considered. In such geometries, the Bloch-point wall (BPW) is the most stable magnetic texture, and as such, the most favored one. The considerable amplitude of the Oesterd field plays a major role in the stabilization of the DW in the ultra-fast dynamic. In particular, this work aimed to quantify the Bloch-point circulation selection phenomenon, observed and described in one of our recent experimental works, with a quantitative theoretical agreement on the value of the threshold current. The micromagnetic simulations have also highlighted the intrinsic complexity of the Bloch-point wall transformations.Cette thèse présente une étude théorique de la dynamique de parois de domaines magnétiques sous courant dans des nanofils magnétiques doux à section circulaire. Ce travail se focalise sur des phénomènes critiques, tels que le piégeage de parois et le changement de leur structure interne. Nous combinons des simulations micromagnétiques avec des descriptions analytiques simplifiées afin de fournir une vue d'ensemble des paramètres clés de cette étude, utiles à la prédiction et à la compréhension des expériences. En particulier, le manuscrit quantifie deux phénomènes critiques. Premièrement, nous nous sommes intéressés au contrôle de la position des parois de domaines. Il peut être exercé à l'aide de modulations de diamètre, créant une barrière de potentiel s'opposant à la propagation, et donc nécessitant un courant de seuil pour la franchir. Pour cela, un modèle analytique a été développé pour des fils de diamètres modérés ( 7 lex) dont les effets avaient été négligés jusqu’à présent. Dans ces géométries, la paroi Point-de-Bloch est la plus favorable des textures magnétiques. L’amplitude du champ Oersted est considérable, jouant un rôle majeur dans la stabilisation de paroi pour la dynamique ultra-rapide. Tout particulièrement, le manuscrit quantifie le phénomène de la sélection de circulation de Point-de-Bloch observé expérimentalement dans un travail récent, avec un accord quantitatif sur le courant de seuil. Les simulations micromagnétiques ont aussi mis en évidence la complexité des transformations de la paroi point-de-Bloch

Theoretical study of current-induced domain wall motion in magnetic nanotubes with azimuthal domains

International audienceWe report a theoretical overview of the magnetic domain wall behavior under an electric current in infinitely-long nanotubes with azimuthal magnetization, combining the $1$D analytic model and micromagnetic simulations. We highlight effects that, besides spin-transfer torques already largely understood in flat strips, arise specifically in the tubular geometry: the \OErsted field and curvature-induced magnetic anisotropy resulting both from exchange and material growth. Depending on both the geometry of the tube and the strength of the azimuthal anisotropy, Bloch or N\'eel walls arise at rest, resulting in two regimes of motion largely dominated by either spin-transfer torques or the \OErsted field. We determine the Walker breakdown current in all cases, and highlight the most suitable parameters to achieve high domain wall speed