Preparation of high-quality planar FeRh thin films for in situ TEM investigations

The preparation of a planar FeRh thin film using a focused ion beam (FIB) secondary electron microscope (SEM) for the purpose of in situ transmission electron microscopy (TEM) is presented. A custom SEM stub with 45° faces allows for the transfer and milling of the sample on a TEM heating chip, whilst Fresnel imaging within the TEM revealed the presence of the magnetic domain walls, confirming the quality of the FIB-prepared sample

Sputter growth and characterization of metamagnetic B2-ordered FeRh epilayers.

Chemically ordered alloys are useful in a variety of magnetic nanotechnologies. They are most conveniently prepared at an industrial scale using sputtering techniques. Here we describe a method for preparing epitaxial thin films of B2-ordered FeRh by sputter deposition onto single crystal MgO substrates. Deposition at a slow rate onto a heated substrate allows time for the adatoms to both settle into a lattice with a well-defined epitaxial relationship with the substrate and also to find their proper places in the Fe and Rh sublattices of the B2 structure. The structure is conveniently characterized with X-ray reflectometry and diffraction and can be visualised directly using transmission electron micrograph cross-sections. B2-ordered FeRh exhibits an unusual metamagnetic phase transition: the ground state is antiferromagnetic but the alloy transforms into a ferromagnet on heating with a typical transition temperature of about 380 K. This is accompanied by a 1% volume expansion of the unit cell: isotropic in bulk, but laterally clamped in an epilayer. The presence of the antiferromagnetic ground state and the associated first order phase transition is very sensitive to the correct equiatomic stoichiometry and proper B2 ordering, and so is a convenient means to demonstrate the quality of the layers that can be deposited with this approach. We also give some examples of the various techniques by which the change in phase can be detected

Quantitative TEM imaging of the magnetostructural and phase transitions in FeRh thin film systems

Equi-atomic FeRh is a very interesting material as it undergoes a magnetostructural transition from an antiferromagnetic (AF) to a ferromagnetic (FM) phase between 75-105 °C. Its ability to present phase co-existence separated by domain walls (DWs) above room temperature provides immense potential for exploitation of their DW motion in spintronic devices. To be able to effectively control the DWs associated with AF/FM coexistence in FeRh thin films we must fully understand the magnetostructural transition and thermomagnetic behaviour of DWs at a localised scale. Here we present a transmission electron microscopy investigation of the transition in planar FeRh thin-film samples by combining differential phase contrast (DPC) magnetic imaging with in situ heating. We perform quantitative measurements from individual DWs as a function of temperature, showing that FeRh on NiAl exhibits thermomagnetic behaviour consistent with the transition from AF to FM. DPC imaging of an FeRh sample with HF-etched substrate reveals a state of AF/FM co-existence and shows the transition from AF to FM regions proceeds via nucleation of small vortex structures, which then grow by combining with newly nucleated vortex states into larger complex magnetic domains, until it is in a fully-FM state

CAGIRE: a wide-field NIR imager for the COLIBRI 1.3 meter robotic telescope

The use of high energy transients such as Gamma Ray Bursts (GRBs) as probes of the distant universe relies on the close collaboration between space and ground facilities. In this context, the Sino-French mission SVOM has been designed to combine a space and a ground segment and to make the most of their synergy. On the ground, the 1.3 meter robotic telescope COLIBRI, jointly developed by France and Mexico, will quickly point the sources detected by the space hard X-ray imager ECLAIRs, in order to detect and localise their visible/NIR counterpart and alert large telescopes in minutes. COLIBRI is equipped with two visible cameras, called DDRAGO-blue and DDRAGO-red, and an infrared camera, called CAGIRE, designed for the study of high redshift GRBs candidates. Being a low-noise NIR camera mounted at the focus of an alt-azimutal robotic telescope imposes specific requirements on CAGIRE. We describe here the main characteristics of the camera: its optical, mechanical and electronics architecture, the ALFA detector, and the operation of the camera on the telescope. The instrument description is completed by three sections presenting the calibration strategy, an image simulator incorporating known detector effects, and the automatic reduction software for the ramps acquired by the detector. This paper aims at providing an overview of the instrument before its installation on the telescope.Comment: Accepted by Experimental Astronom

Observation of a temperature dependent asymmetry in the domain structure of a Pd-doped FeRh epilayer

Using X-ray photoelectron emission microscopy we have observed the coexistence of ferromagnetic and antiferromagnetic phases in a (3 at.%)Pd-doped FeRh epilayer. By quantitatively analyzing the resultant images we observe that as the epilayer transforms there is a change in magnetic domain symmetry from predominantly twofold at lower temperatures through to an equally weighted combination of both four and twofold symmetries at higher temperature. It is postulated that the lowered symmetry Ising-like nematic phase resides at the near-surface of the epilayer. This behavior is different to that of undoped FeRh suggesting that the variation in symmetry is driven by the competing structural and electronic interactions in the nanoscale FeRh film coupled with the effect of the chemical doping disorder.Comment: 10 pages, 8 figures, 1 tabl

Strain-tuning of the magnetocaloric transition temperature in model FeRh films

The chemically ordered B2 phase of equiatomic FeRh is known to absorb or evolve a significant latent heat as it traverses its first-order phase transition in response to thermal, magnetic, and mechanical drivers. This attribute makes FeRh an ideal magnetocaloric material testbed for investigation of relationships between the crystalline lattice and the magnetic spins, which are especially experimentally accessible in thin films. In this work, epitaxial FeRh films of nominal 30 nm and 50 nm thicknesses with out-of-plane c-axis orientation were sputter-deposited at high temperature onto (0 0 1)-MgO or (0 0 0 1)-Al2O3 substrates and capped with Al, Au, Cr, or W after in situ annealing at 973 K to promote CsCl-type chemical order. In this manner a controlled strain state was invoked. Experimental results derived from laboratory and synchrotron x-ray diffraction combined with magnetometry indicate that the antiferromagnetic (AF)—ferromagnetic (FM) magnetostructural phase transformation in these films may be tuned over an ~50° range (373 K–425 K) through variation in the c/a ratio derived from lattice strain delivered by the substrate and the capping layers. These results supply fundamental information that might be used to engineer the magnetocaloric working material in new system designs by introducing targeted values of passive strain to the system

Prise en charge des pathologies traumatiques des membres inférieurs et supérieurs à l’officine : guide de conseil sur la réalisation de bandages de type « strapping »

The making of a strapping consists of using an adhesive and elastic (or not) bandage to treat someone who’s suffering a trauma or to prevent it. Although using mainly by physiotherapists, the pharmacist can bandage someone in its pharmacy. However, he will never be able to make a diagnosis following a trauma, this task will be kept for a physician. Strapping can compress an injury, allowing to improve the removing of oedema and the healing process, while avoiding immobilization which is now known to be ineffective in recovery. This work consists to make accessible strapping techniques, and offer a booklet facilitating their making.Réaliser un strapping consiste à utiliser une bande adhésive et élastique (ou non) pour prendre en charge ou prévenir un traumatisme. Bien qu’utilisée principalement par le kinésithérapeute, le pharmacien pourra très bien réaliser des bandages dans son officine. Il ne devra par contre jamais réaliser un diagnostic suite à un traumatisme récent, ce rôle étant réservé au médecin. Le strapping va comprimer la blessure, ce qui permet d’améliorer l’évacuation de l’œdème, renforcer la cicatrisation, tout en évitant l’immobilisation qui est reconnue comme délétère à une bonne récupération aujourd’hui. Ce travail consiste à rendre les techniques de strapping plus accessibles et proposer un livret en facilitant la réalisation

The effects of different cations on the physicochemical characteristics of casein micelles

Physicochemical characterisation of casein micelles suspended in milk ultrafiltrate and enriched with different cations (Fe, Cu, Ca, Zn and Mg) was investigated. After addition of 2.5–8.0 mmol kg−1 of cations, associations of added cation, citrate, inorganic phosphate and calcium with casein micelles were observed. The order of association of cations with casein micelles was Fe3+ > Zn2+ > Ca2+ > Cu2+ > Mg2+. At the same time, the casein content increased in the casein micelles while the water content decreased. Changes in hydrophobicity and zeta potential of casein micelles were also determined while no variation in the average diameter was detected. In the presence of 8.0 mmol kg−1 of magnesium or ferric iron, heat stability (115 °C for 30 min) of casein micelles was decreased. From these results, a mechanism of cation association with casein micelles is proposed, highlighting the determinant role of ultrafiltrable citrate and inorganic phosphate. This mechanism is discussed in relation to modifications in physicochemical characteristics of casein micelles

Nano-structures ferromagnétique - anti-ferromagnétique pour applications en hyperfréquences

L'axe de recherche développé au cours de la thèse a particulièrement été focalisé sur l utilisation de matériaux nouveaux pour des applications en haut de bande HP. Afin de satisfaire de telles exigences, il convient de concevoir des matériaux ayant la particularité de posséder des valeurs de permittivité et de perméabilité élevées dans les fréquences micro-ondes comprises entre 1 et 20 gigahertz. Cette dernière propriété nécessite d élaborer des matériaux à anisotropie magnétique uniaxiale bien définie, à forte aimantation à saturation et à coercitivité faible, les deux premières propriétés étant difficilement compatibles. La motivation initiale de ce travail porte ainsi sur l élaboration, l optimisation et l étude de la dynamique de spin à haute fréquence de structures multicouches d épaisseur nanométrique de type ferromagnétique/isolant, avec les ferromagnétiques choisis NiFe et CoFeZr et les isolants de type diamagnétique Al203 et anti-ferromagnétique NiO. Le couplage avec la couche de NiO permet d induire une anisotropie unidirectionnelle. De plus, nous nous sommes particulièrement intéressés aux effets de dimensionnalité réduite sur les propriétés magnétiques dynamiques. Afin d élaborer ces matériaux, nous avons mené une étude systématique des paramètres magnétiques statiques et structuraux en fonction des conditions de dépôt. Cela nous a permis de sélectionner les conditions de croissance appropriées et de mettre en évidence la corrélation entre les propriétés structurales et magnétiques. Les performances dynamiques de ces matériaux (CoFeZr) les placent comme de bons candidats pour certaines applications RF nécessitant à la fois une perméabilité et des fréquences de résonance élevées. Les mesures systématiques conduites sur les deux structures à base de Py et de CoFeZr, nous ont permis de dégager, d une part, le rôle clé de l interface pour ces matériaux aux épaisseurs concernées, mais aussi d évaluer les différents termes d anisotropie présents et notamment un comportement remarquable de l anisotropie uniaxiale pour les systèmes Py/Al2O3 avec le basculement de l axe d anisotropie à une épaisseur critique de 5 nm. De plus, un traitement par analyse REM et l utilisation du modèle de Meiklejohn et Bean nous permettent de déterminer le désalignement entres les axes d anisotropie des systèmes couplés par échange, ce qui peut se révéler complexe selon d autre méthode. Dans l étude de la relaxation magnétique, nous avons utilisé les larges possibilités de la résonance ferromagnétique large bande afin de discriminer et de quantifier les différentes contributions à la relaxation des différents systèmes étudiés. Un point fort de cette étude de la relaxation magnétique est l observation et la quantification de l anisotropie de l amortissement intrinsèque (aG) induite et surtout proportionnelle au couplage d échange.The aim of the research developed during the thesis has been particularly focused on new materials for applications in high-band RF. To meet such requirements, it should be developed materials with hight permittivity and hight permeability (in the high microwave frequencies between 1 and 20 gigahertz). This last property requires to develop materials to well-defined uniaxial magnetic anisotropy, high saturation magnetization and low coercivity, the first two properties are hardly compatible. The initial motivation of this work involves the development, optimisation and the study of spin dynamics at high frequency multilayer structures with nanometer-thick type ferromagnet / insulator with ferromagnetic NiFe and selected CoFeZr and insulators diamagnetic type Al203 and antiferromagnetic NiO. Coupling with the NiO layer can induce a unidirectional anisotropy. In addition, we focused on the effects of reduced dimensionality on the dynamic magnetic properties. To elaborate these materials, we conducted a systematic study of static magnetic and structural parameters based on the deposition conditions. This allowed us to select the appropriate growth conditions and to highlight the correlation between the structural and magnetic properties. The dynamic performance of these materials (CoFeZr) are interesting for RF applications requiring both permeability and higher resonance frequencies. Routine measurements conducted on the two structures based on Py and CoFeZr allowed us to identify the one hand, the key role of the interface for these materials with thicknesses involved, but also to evaluate the different terms anisotropy including a noteworthy behavior of the uniaxial anisotropy for systems with Py/A1203, the tilting of the anisotropy axis at critical thickness around 5 nm. Additionally treatment by RFM analysis and use of Meiklejohn and Beau model we can determine the misalignment between the axes of anisotropy in exchange coupled systems, this may be complicated by other method. In the study of magnetic relaxation, we used appropriate method to broadband RFM to discriminate and quantify relaxation s contributions of different systems. A important point of this study of relaxation magnetic is observation and quantification of the anisotropy of the intrinsic damping (aG), mainly proportional to the exchange coupling.BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF