High-resolution scanning transmission X-ray microscopy (STXM) can provide quantitative access to the tilt angles of the local magnetization with respect to the surface. We use this state-of-the-art microscopy technique to probe the magnetic texture of the weak stripes texture hosted by a 180 nm thick Co40Fe40B20 layer. We report a comprehensive set of measurements of the weak stripes texture tilt angle, as well as a method that uses only a single direction x-ray beam to extract the angle. This method also extracts the spatial profile with 30 nm resolution and measures the tilt angle as a function of the applied field. Combining these informations, the macroscopic loop of magnetization as a function of applied field on a complex spin texture can be reconstructed in an unprecedented way and shows without doubt that flux closure domains exist. Beyond the characterization of the weak stripe angle, this quantitative magnetic X-ray microscopy technique can be used to study the local textures present in all materials exhibiting some circular magnetic X-ray dichroism.
In this work , we describe the design, realisation and characterization of the magnetic version of the Galton Board, an archetypal statistical device originally designed to exemplify normal distributions. Although simple in its macroscopic form, achieving an equivalent nanoscale system poses many challenges related to the generation of sufficiently similar nanometric particles and the strong influence that nanoscale defects can have in the stochasticity of random processes. We demonstrate how the quasi-particle nature and the chaotic dynamics of magnetic domain-walls can be harnessed to create nanoscale stochastic devices [1]. Furthermore, we show how the direction of an externally applied magnetic field can be employed to controllably tune the probability distribution at the output of the devices, and how the removal of elements inside the array can be used to modify such distribution.
Recently, there has been impressive progress in the field of artificial intelligence. A striking example is Alphago, an algorithm developed by Google, that defeated the world champion Lee Sedol at the game of Go. However, in terms of power consumption, the brain remains the absolute winner, by four orders of magnitudes. Indeed, today, brain inspired algorithms are running on our current sequential computers, which have a very different architecture than the brain. If we want to build smart chips capable of cognitive tasks with a low power consumption, we need to fabricate on silicon huge parallel networks of artificial synapses and neurons, bringing memory close to processing. The aim of the presented work is to deliver a new breed of bio-inspired magnetic devices for pattern recognition. Their functionality is based on the magnetic reversal properties of an artificial spin ice in a Kagome geometry for which the magnetic switching occurs by avalanches.
Yann Perrin, Ioan Chioar, Hanna Riahi, Van Nguyen, Aurélien Masseboeuf, Christophe Gatel, Stefan McMurtry, Benito Santos Burgos, Tevfik Onur Mentes, Andrea Locatelli, Jean-Christophe Toussaint, François Montaigne, Daniel Lacour, Nicolas Rougemaille, Benjamin Canals, Michel Hehn
Complex architectures of nanostructures are currently routinely elaborated using bottom-up or nanofabrication processes. This technological capability allows scientists to engineer materials with properties that do not exist in nature, but also to manufacture model systems to explore fundamental issues in condensed matter physics. Two-dimensional frustrated arrays of magnetic nanostructures are one class of systems for which theoretical predictions can now be tested experimentally.
In particular, magnetic imaging techniques offer the appealing opportunity to observe a wide range of phenomena within the concept of lab-on-a-chip. For example, several exotic magnetic phases have been discovered in artificial frustrated spin systems. Besides, these systems allow the study of classical analogues of magnetic monopoles. These recent results have stimulated new research activities motivated by the quest for magnetic monopoles in condensed matter physics.
In this contribution, we'll show that the micromagnetic properties of the elements constituting artificial frustrated arrays of nanomagnets introduce the concept of chiral monopoles. Injecting and manipulating experimentally the chirality of a magnetic monopole provide a new degree of freedom in the system. This offers the opportunity to control their motion under an external magnetic field, thus allowing to envision applications in magnetronics.
In a context where sub-micrometric magnetic dots are foreseen to play an active role in various new breeds of electronics components such as magnetic memories, magnetic logics or bio-sensors, the use of micromagnetic simulations to optimize their shapes and spatial arrangement with respect to a chosen application has become unavoidable. Prior realizing experimentally magnetic dots presenting four stable magnetic states (4SMS), we performed a micromagnetic study to select a design providing not only four equivalent magnetic states in a single dot but also exhibiting mostly uniform magnetic states.
U. Halisdemir, F. Schleicher, D. J. Kim, B. Taudul, D. Lacour, W. S. Choi, M. Gallart, S. Boukari, G. Schmerber, V. Davesne, P. Panissod, D. Halley, H. Majjad, Y. Henry, B. Leconte, A. Boulard, D. Spor, N. Beyer, C. Kieber, E. Sternitzky, O. Cregut, M. Ziegler, F. Montaigne, J. Arabski, E. Beaurepaire, W. Jo, M. Alouani, P. Gilliot, M. Hehn, M. Bowen
The conservation of an electron’s spin and symmetry as it undergoes solid-state tunnelling within magnetic tunnel junctions (MTJs) is thought to be best understood using MgO-based MTJs1. Yet the very large experimental values of tunnelling magnetoresistance (TMR) that justify this perception are often associated with tunnelling barrier heights well below those suggested by the MgO optical band gap. This combination of high TMR and low RA-product, while spawning spin-transfer/spin-orbit torque experiments and considerable industrial interest, cannot be explained by standard theory. Noting the impact of a tunnel barrier’s altered stoichiometry on TMR2, we reconcile this 10+year-old contradiction between theory and experiment by considering the impact of the MgO barrier’s structural defects3–5. We find that the ground and excited states of oxygen vacancies can promote localized states within the band gap with differing electronic character. By setting symmetry- and temperature-dependent tunnelling barrier heights, they alter symmetry-polarized tunnelling and thus TMR. We will examine how annealing, depending on MgO growth conditions, can alter the nature of these localized states. This oxygen vacancy paradigm of inorganic tunnelling spintronics opens interesting perspectives into endowing the MTJ with additional functionalities, such as optically manipulating the MTJ’s spintronic response.
Complex architectures of nanostructures are routinely elaborated using bottom-up or nanofabrication processes. This technological capability allows scientists to engineer materials with properties that do not exist in nature, but also to manufacture model systems to explore fundamental issues in condensed matter physics. Two-dimensional frustrated arrays of magnetic nanostructures are one class of systems for which theoretical predictions can be tested experimentally. These systems have been the subject of intense research in the last few years and allowed the investigation of a rich physics and fascinating phenomena, such as the exploration of the extensively degenerate ground-state manifolds of spin ice systems, the evidence of new magnetic phases in purely two-dimensional lattices, and the observation of pseudoexcitations involving classical analogues of magnetic monopoles. We show here, experimentally and theoretically, that simple magnetic geometries can lead to unconventional, non-collinear spin textures. For example, kagome arrays of inplane magnetized nano-islands do not show magnetic order. Instead, these systems are characterized by spin textures with intriguing properties, such as chirality, coexistence of magnetic order and disorder, and charge crystallization. Magnetic frustration effects in lithographically patterned kagome arrays of nanomagnets with out-of-plane magnetization also lead to an unusal, and still unknown, magnetic ground state manifold. Besides the influence of the lattice geometry, the micromagnetic nature of the elements constituting the arrays introduce the concept of chiral magnetic monopoles, bringing additional complexity into the physics of artificial frustrated spin systems.
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