Three-Dimensional Magnetic Page Memory

The increasing need to store large amounts of information with an ultra-dense, reliable, low power and low cost memory device is driving aggressive efforts to improve upon current perpendicular magnetic recording technology. However, the difficulties in fabricating small grain recording media while maintaining thermal stability and a high signal-to-noise ratio motivate development of alternative methods, such as the patterning of magnetic nano-islands and utilizing energy-assist for future applications. In addition, both from sensor and memory perspective three-dimensional spintronic devices are highly desirable to overcome the restrictions on the functionality in the planar structures. Here we demonstrate a three-dimensional magnetic-memory (magnetic page memory) based on thermally assisted and stray-field induced transfer of domains in a vertical stack of magnetic nanowires with perpendicular anisotropy. Using spin-torque induced domain shifting in such a device with periodic pinning sites provides additional degrees of freedom by allowing lateral information flow to realize truly three-dimensional integration

Thermally induced magnetic switching in bit-patterned media

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Applied Physics 122, 043907 (2017) and may be found at https://doi.org/10.1063/1.4992808.We have studied the thermal variation of the switching field of magnetic islands at room temperature. A model bit-pattern media composed of an assembly of islands with 80 nm width was fabricated by sputter deposition onto a pre-patterned substrate. Using direct magnetic-contrast imaging of the islands under applied field, we extract the switching probabilities of individual islands. Based on an analytical model for the thermally activated switching of the islands, we are able to determine the intrinsic magnetic anisotropy of each island and, consequentially, a distribution of anisotropies for the island ensemble investigated. In the distribution, we identify a separated group of islands with a particularly small anisotropy. We attribute this group to islands containing misaligned grains triggering the magnetic reversal. At room temperature and slow field sweep rates, the observed thermal broadening of the switching-field distribution is small compared to the intrinsic broadening. However, we illustrate that thermal fluctuations play a crucial role at high sweep rates by extrapolating our results to technological relevant regimes

Magnetic remanent states in antiferromagnetically coupled multilayers

In antiferromagnetically coupled multilayers with perpendicular anisotropy unusual multidomain textures can be stabilized due to a close competition between long-range demagnetization fields and short-range interlayer exchange coupling. In particular, the formation and evolution of specific topologically stable planar defects within the antiferromagnetic ground state, i.e. wall-like structures with a ferromagnetic configuration extended over a finite width, explain configurational hysteresis phenomena recently observed in [Co/Pt(Pd)]/Ru and [Co/Pt]/NiO multilayers. Within a phenomenological theory, we have analytically derived the equilibrium sizes of these "ferroband" defects as functions of the antiferromagnetic exchange, a bias magnetic field, and geometrical parameters of the multilayers. In the magnetic phase diagram, the existence region of the ferrobands mediates between the regions of patterns with sharp antiferromagnetic domain walls and regular arrays of ferromagnetic stripes. The theoretical results are supported by magnetic force microscopy images of the remanent states observed in [Co/Pt]/Ru.Comment: Paper submitted by the Joint European Magnetics Symposia 2008, Dublin (4 pages, 3 figures

Conditioning Medicine A new pharmacological preconditioning-based target: from drosophila to kidney transplantation

International audienceOne of the biggest challenges in medicine is to dampen the pathophysiological stress induced by an episode of ischemia. Such stress, due to various pathological or clinical situations, follows a restriction in blood and oxygen supply to tissue, causing a shortage of oxygen and nutrients that are required for cellular metabolism. Ischemia can cause irreversible damage to target tissue leading to a poor physiological recovery outcome for the patient. Contrariwise, preconditioning by brief periods of ischemia has been shown in multiple organs to confer tolerance against subsequent normally lethal ischemia. By definition, preconditioning of organs must be applied preemptively. This limits the applicability of preconditioning in clinical situations, which arise unpredictably, such as myocardial infarction and stroke. There are, however, clinical situations that arise as a result of ischemia-reperfusion injury, which can be anticipated, and are therefore adequate candidates for preconditioning. Organ and more particularly kidney transplantation, the optimal treatment for suitable patients with end stage renal disease (ESRD), is a predictable surgery that permits the use of preconditioning protocols to prepare the organ for subsequent ischemic/reperfusion stress. It therefore seems crucial to develop appropriate preconditioning protocols against ischemia that will occur under transplantation conditions, which up to now mainly referred to mechanical ischemic preconditioning that triggers innate responses. It is not known if preconditioning has to be applied to the donor, the recipient, or both. No drug/target pair has been envisioned and validated in the clinic. Options for identifying new target/drug pairs involve the use of model animals, such as drosophila, in which some physiological pathways, such as the management of oxygen, are highly conserved across evolution. Oxygen is the universal element of life existence on earth. In this review we focus on a very specific pathway of pharmacological preconditioning identified in drosophila that was successfully transferred to mammalian models that has potential application in human health. Very few mechanisms identified in these model animals have been translated to an upper evolutionary level. This review highlights the commonality between oxygen regulation between diverse animals

The Paramagnetic Meissner Effect (PME) in Metallic Superconductors

The experimental data in the literature concerning the Paramagnetic Meissner Effect (PME) or also called Wohlleben effect are reviewed with the emphasis on the PME exhibited by metallic, s-wave superconductors. The PME was observed in field-cool cooling (FC-C) and fieldcool warming (FC-W) m(T)-measurements on Al, Nb, Pb, Ta, in compounds such as, e.g., NbSe2, In-Sn, ZrB12, and others, and also in MgB2, the metallic superconductor with the highest transition temperature. Furthermore, samples with different shapes such as crystals, polycrystals, thin films, biand multilayers, nanocomposites, nanowires, mesoscopic objects, and porous materials exhibited the PME. The characteristic features of the PME, found mainly in Nb disks, such as the characteristic temperatures T1 and Tp and the apparative details of the various magnetic measurement techniques applied to observe the PME, are discussed. We also show that PME can be observed with the magnetic field applied parallel and perpendicular to the sample surface, that PME can be removed by abrading the sample surface, and that PME can be introduced or enhanced by irradiation processes. The PME can be observed as well in magnetization loops (MHLs, m(H)) in a narrow temperature window Tp < Tc, which enables the construction of a phase diagram for a superconducting sample exhibiting the PME. We found that the Nb disks still exhibit the PME after more than 20 years, and we present the efforts of magnetic imaging techniques (scanning SQUID microscopy, magneto-optics, diamond nitrogen-vacancy (NV)-center magnetometry, and low-energy muon spin spectroscopy, (LE-µSR)). Various attempts to explain PME behavior are discussed in detail. In particular, magnetic measurements of mesoscopic Al disks brought out important details employing the models of a giant vortex state and flux compression. Thus, we consider these approaches and demagnetization effects as the base to understand the formation of the paramagnetic signals in most of the materials investigated. New developments and novel directions for further experimental and theoretical analysis are also outlined

Effets de la température et d'un transporteur naturel d'oxygène au cours de la conservation en transplantation rénale

La méthode de préservation d organes la plus utilisée actuellement en transplantation rénale est la conservation statique en hypothermie. Cependant, ce mode de conservation induit des dommages inhérents aux lésions du syndrome d ischémie/reperfusion (I/R). Cette étude a eu pour objectif d identifier de nouvelles conditions de préservation des greffons, afin de limiter les lésions d I/R, en modulant la température de conservation ou par ajout d un transporteur d oxygène. Nous avons utilisé deux modèles : in vitro avec des cellules endothéliales et in vivo en autotransplantation rénale chez le porc.Les résultats ont confirmé les effets délétères de la conservation à 4C contrairement à des conservations à 19C, 27C et surtout 32C, permettant d obtenir une activité métabolique, une viabilité et une intégrité cellulaire supérieures ainsi qu une diminution des marqueurs de l inflammation et du stress oxydant. Nous avons aussi démontré les bénéfices d'un nouveau transporteur d oxygène, M101, dans deux des solutions de conservation les plus utilisés, UW et HTK. L'utilisation de M101 en conservation statique permet une meilleure reprise de fonction à court terme et une réduction de la fibrose, cause principale de la perte du greffon. Enfin, nous avons montré une conservation des bénéfices de M101 à des doses réduites et déterminé que cette protection était due à une multifonctionnalité de la molécule, combinant un transporteur d oxygène, une activité superoxyde dismutase et une taille importante (permettant de réguler la pression oncotique). Ce travail a montré de nouvelles pistes de réflexion vers une préservation, et donc une qualité, supérieure des organes à transplanter.The most used preservation method in renal transplantation is hypothermic cold storage (CS). However, this method induces damages inherent to the ischemia/ reperfusion (I /R) syndrome.My study was aimed at identifying new grafts preservation conditions, to limit I/R damage, by varying storage temperature or by adding an oxygen carrier.We used two models: in vitro with endothelial cells and in vivo in pig renal autotransplantation. The results confirmed the deleterious effects of 4C storage in contrast to conservations at 19C, 27C and above 32C, resulting in improved metabolic activity, cellular viability and integrity as well as a significant reduction in markers of inflammation and oxidative stress. Then we demonstrated the benefits of a new oxygen carrier, M101, in the two most used preservation solutions, UW and HTK. Indeed, use of M101 in CS protocols improved short-term function recovery and reduced fibrosis development, main cause of graft loss. Finally, we have shown that the benefits of M101 were preserved at lower doses and we determined that this protection was due to a multifunctionality of the molecule, combining oxygen transport, superoxyde dismutase activity and a large size (regulating oncotic pressure). This work permitted the uncovering of new concepts towards improved organ preservation and quality for transplantation.POITIERS-SCD-Bib. électronique (861949901) / SudocSudocFranceF