Propriétés magnétostatiques de réseaux de nanofils via les courbes de renversement du premier ordre

Courbes de renversement du premier ordre -- Concepts de base -- Philosophie d'utilisation actuelle -- Méthodologie -- Acquisition d'un ensemble de courbes de renversement du premier ordre -- Processus réversibles -- Processus irréversibles -- Présentation et caractérisation des résultats FORC -- Interprétation des résultats FORC via le modèle d'analyse physique -- Réseaux de nanofils ferromagnétiques -- Structure -- Dispositifs à haute fréquence -- Fabrication des réseaux -- Caractérisation magnétique -- Réseaux de nanofils uniformes -- Échantillons -- Comportement axial -- Comportement transverse -- Synthèse -- Réseaux de nanofils multicouches -- Anisotropie

Stabilizing Zero-Field Skyrmions at Room-Temperature in Perpendicularly Magnetized Multilayers

Magnetic skyrmions are twirling spin structures observed in bulk, thin films, and multilayers with several features for both fundamental physics understanding and spintronic applications, i.e., nanoscale size, efficient transport under electrical current, and topological protection against defects. However, most magnetic skyrmions have been observed under the assistance of an out-of-plane magnetic field, which may limit their use in magnetic memory technologies. In this chapter, we review and present two recent mechanisms to create zero-field skyrmions at room-temperature in ferromagnetic multilayers. First, by tuning the perpendicular magnetic anisotropy (PMA) and remnant magnetization (near magnetization saturation) in unpatterned symmetric multilayer systems, it was achieved a transition from worm-like domains to isolated skyrmions. Besides, we present how to find stable zero-field skyrmions in arrays of ferrimagnetic discs by tailoring their diameter. Both methods demonstrate a robust route to stabilize zero-field skyrmions at room temperature, thus providing an important contribution to possible applications of these textures in the next generation of skyrmionics devices

Electrical Manipulation of a Single Nanowire by Dielectrophoresis

Nanowires (NWs), due to their unique highly anisotropic characteristics, hold a great promise to be used in wide technological fields, such as building blocks for data storage and memory, advanced scanning probes, and biotechnological applications. In addition, given the high sensitivity to their environment, NWs can be used as sensor for a number of applications. The fabrication and electrical characterization of NW‐based devices can be achieved after proper placing of NWs between electrodes, which represents one of the major challenges in this field. The dielectrophoresis (DEP) method can be used to trap electrically neutral NWs by the application of an alternating electric field between a pair of electrodes. Here, we present a systematic study of DEP parameters as well as electrodes geometry for NW deposition. This method presents a suitable protocol for deposition in a useful and coherent fashion of post‐growth electrodeposited NWs and further electrical characterization. This can be used for investigation of the fundamental transport properties of individual NWs and fabrication of NW‐based devices, such as sensors and field‐effect transistors

How to Characterize Cylindrical Magnetic Nanowires

Cylindrical magnetic nanowires made through the help of nanoporous alumina templates are being fabricated and characterized since the beginning of 2000. They are still actively investigated nowadays, mainly due to their various promising applications, ranging from high-density magnetic recording to high-frequency devices, passing by sensors, and biomedical applications. They also represent suitable systems in order to study the dimensionality effects on a given material. With time, the development in fabrication techniques allowed to increase the obtained nanowire complexity (controlled crystallinity, modulated composition and/or geometry, range of materials, etc.), while the improvements in nanomanipulation permitted to fabricate system based either on arrays or on single nanowires. On the other side, their increased complexity requires specific physical characterization methods, due to their particular features such as high anisotropy, small magnetic volume, dipolar interaction field between them, and interesting electronic properties. The aim of this chapter was to offer an ample overview of the magnetic, electric, and physical characterization techniques that are suitable for cylindrical magnetic nanowire investigation, of what is the specific care that one needs to take into account and which information will be extracted, with typical and varied examples

Large-area nanopillar arrays by glancing angle deposition with tailored magnetic properties

Ferromagnetic films down to thicknesses of tens of nanometers and composed by polycrystalline Fe and Fe2O3 nanopillars are grown in large areas by glancing angle deposition with magnetron sputtering (MS-GLAD). The morphological features of these films strongly depend on the growth conditions. Vertical or tilted nanopillars have been fabricated depending on whether the substrate is kept rotating azimuthally during deposition or not, respectively. The magnetic properties of these nanopillars films, such as hysteresis loops squareness, adjustable switching fields, magnetic anisotropy and coercivity, can be tuned with the specific morphology. In particular, the growth performed through a collimator mask mounted onto a not rotating azimuthally substrate produces almost isolated well-defined tilted nanopillars that exhibit a magnetic hardening. The first-order reversal curves diagrams and micromagnetic simulations revealed that a growth-induced uniaxial anisotropy, associated with an anisotropic surface morphology produced by the glancing angle deposition in the direction perpendicular to the atomic flux, plays an important role in the observed magnetic signatures. These results demonstrate the potential of the MS-GLAD method to fabricate nanostructured films in large area with tailored structural and magnetic properties for technological applications

Novel magnetic nanostructures: nanopillars and patterned antidots

Resumen del trabajo presentado en el Simposio Nuevas fronteras y retos en Magnetismo de la XXXVIII Reunión Bienal de la Real Sociedad Española de Física, celebrada en Murcia (España), del 11 al 15 de julio de 2022Two different nanostructures are studied in this contribution: large-area nanopillar arrays fabricated by glancing angle deposition with magnetron sputtering (MS-GLAD) and magnetic thin films perforated with long-range order arrays of nanoholes prepared by focused ion beam (patterned antidots). MS-GLAD is an easy and versatile route to fabricate arrays of nanostructures in large areas in a single processing step. In our work, nanostructured films with vertical or tilted nanopillars composed by polycrystalline Fe and Fe2O3 have been fabricated depending on whether the substrate is kept rotating azimuthally during deposition or not, respectively [1]. The magnetic properties of these films can be tuned with the specific morphology. In particular, the growth performed through a collimator mask mounted onto a not rotating azimuthally substrate produces almost isolated well-defined tilted nanopillars that exhibit a magnetic hardening. The first-order reversal curves diagrams and micromagnetic simulations revealed that a growth-induced uniaxial anisotropy, associated with an anisotropic surface morphology produced by the GLAD in the direction perpendicular to the atomic flux, plays an important role in the observed magnetic signatures. Magnetic antidots are being studied for different applications, such as magnonic crystals for microwave devices, magnetically-active plasmonic media, magnetic biosensing, and magneto-resistance sensors. In our work, a top-down approach using focused ion beam has been employed to fabricate Co/Permalloy hard-soft bilayer antidot arrays [2]. The antidots have a 40 nm diameter and two symmetries are studied: square and hexagonal. A dependence of magnetic coercivity on the relative thicknesses of the magnetically hard (Co) and soft (Permalloy) layers is found; increasing Permalloy thickness results in lower magnetic coercivity. Furthermore, the long-range periodicity of these antidots results in higher magnetic coercivity and a stronger magnetic domain-wall pinning, compared to identical hard/soft bilayers of short-range order deposited on porous anodic alumina. Finally, magnetic force microscopy (MFM) imaging of the antidot arrays shows striking qualitative differences between the two symmetries: square symmetry arrays have inhomogeneous magnetic state and a high density of immobile super-domain walls, whereas hexagonal symmetry arrays show a homogeneous magnetic configuration.The service from the MiNa Laboratory at IMN. Funding from MINECO, Comunidad de Madrid, European Union, Fondecyt, Dicyt-Usach, São Paulo Research Foundation, Brazilian National Council for S., NSRF Greece-EU, NATO

Magnetic properties of spinel-type oxides NiMn2-xMexO4

New materials, based on the well-known spinel compound NiMn2O4, have been synthesized and characterized from the magnetic point of view. The manganese cation was partially substituted in the general formula NiMn2-xMexO4 , by nonmagnetic and magnetic elements, such as Me = Ga, Zn, Ni and Cr (0 x 1). Prior to the determination of their magnetic properties, the non-substituted spinel NiMn2O4 was carefully characterized and studied as a function of the oxygen stoichiometry, based on the influence of the annealing atmosphere and quenching rate. The ferrimagnetic character was observed in all samples, with a paramagnetic-to-ferromagnetic transition temperature Tc stabilized at 110 K, and well defined long-range antiferromagnetic interactions at lower temperatures, which depend on the applied field and the substitute concentrationAuthors from Chile and O.P. thank projects Fondecyt-Chile 1020066, 7020066 and 1050178. Authors from France and Brazil thank project CAPES/COFECUB 416/03. Authors from France thank Région Bretagne for financial supportPeer reviewe

Propriétés magnétostatiques de nanofils ferromagnétiques et interactions dues à l'effet du réseau

État de la question -- Problématique -- Solution envisagée -- Méthodologie -- Fabrication de réseaux de nanofils ferromagnétiques -- Préparation des échantillons -- Électrodéposition -- Réseaux de nanofils -- Caractérisation magnétique : notion de base -- Magnétomètre à échantillon vibrant : principe de fonctionnement -- Informations magnétiques -- Méthode des courbes de renversement du premier ordre -- Interprétation des diagrammes -- Artefacts -- Caractérisation magnétostatique à partir de diagrammes FORC -- Extraction des résultats à partir d'un diagramme FORC OOP