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Uranium dioxide (UO2) and metaschoepite (UO3•nH2O) particles have been identified as contaminants at nuclear sites. Understanding their behavior and impact is crucial for safe management of radioactively contaminated land and to fully understand U biogeochemistry. The Savannah River Site (SRS) (South Carolina, USA), is one such contaminated site, following historical releases of U-containing wastes to the vadose zone. Here, we present an insight into the behavior of these two particle types under dynamic conditions representative of the SRS, using field lysimeters (15 cm D x 72 cm L). Discrete horizons containing the different particle types were placed at two depths in each lysimeter (25 cm and 50 cm) and exposed to ambient rainfall for 1 year, with an aim of understanding the impact of dynamic, shallow subsurface conditions on U particle behavior and U migration. The dissolution and migration of U from the particle sources and the speciation of U throughout the lysimeters was assessed after 1 year using a combination of sediment digests, sequential extractions, and bulk and μ-focus X-ray spectroscopy. In the UO2 lysimeter, oxidative dissolution of UO2 and subsequent migration of U was observed over 1–2 cm in the direction of waterflow and against it. Sequential extractions of the UO2 sources suggest they were significantly altered over 1 year. The metaschoepite particles also showed significant dissolution with marginally enhanced U migration (several cm) from the sources. However, in both particle systems the released U was quantitively retained in sediment as a range of different U(IV) and U(VI) phases, and no detectable U was measured in the lysimeter effluent. The study provides a useful insight into U particle behavior in representative, real-world conditions relevant to the SRS, and highlights limited U migration from particle sources due to secondary reactions with vadose zone sediments over 1 year.

The ability to tune the competition between the in-plane and out-of-plane orientation of magnetization provides a means to construct thermal sensors with a sharp spin re-orientation transition at specific temperatures. We have observed such a tuneable, temperature driven spin re-orientation in structurally amorphous, ferrimagnetic rare earth-transition metal (RE-TM) alloy thin films using scanning transmission X-ray microscopy (STXM) and magnetic measurements. The nature of the spin re-orientation transition in FeGd can be fully explained by a non-equilibrium, nanoscale modulation of the chemical composition of the films. This modulation leads to a magnetic domain pattern of nanoscale speckles superimposed on a background of in-plane domains that form Laudau configurations in micron-scale patterned elements. It is this speckle magnetic structure that gives rise to a sharp two step-reversal mechanism that is temperature dependent. The possibility to balance competing anisotropies through the temperature opens opportunities to create and manipulate topological spin textures.

Despite the excellent catalytic properties of individual nanoparticles and atomic clusters, the cur-rent capabilities to assemble them into a complex system are insufficient for many practical appli-cations. An objective of this work is to develop a fabrication technology that allows for the simul-taneous control of the nanoparticle surface chemistry, elemental distribution, microscale geometry, and large-scale assembly. Using a cellulose structure derived from wood, we fabricated hierar-chical porous cellulose scaffolds combined with cerium-doped TiO2. This hybrid material served as the support for atomically dispersed Pt catalysts and was used to successfully decompose eth-ylene at zero degrees Celsius. The fabrication concept developed in this work would allow miti-gating the conflict between the required large active surfaces and the difficulties in handling na-nopowders in environmental catalysis, including food preservation and indoor air purification. We thus discovered a promising route to manufac...

International audience; Traces of Pu have been detected in material released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March of 2011; however, to date the physical and chemical form of the Pu have remained unknown. Here we report the discovery of particulate Pu associated with cesium-rich microparticles (CsMPs) that formed in and were released from the reactors during the FDNPP meltdowns. The Cs-pollucite-based CsMP contained discrete U(IV)O2 nanoparticles

This paper presents an efficient colloidal approach to process CoFe2O4 and SiO2 nanoparticles into thin films for magnetic and magneto-optical applications. Thin films of varying CoFe2O4-to-SiO2 ratios (from 0 to 90 wt%) are obtained by sequential spin coating-calcination cycles from the corresponding nanoparticle dispersions. Scanning electron microscopy analysis reveals a crack free and nanoparticulate structure of the sintered films with thicknesses of 480–1200 nm. Results from the optical characterization indicate a direct band gap ranging from 2.6 to 3.9 eV depending on the SiO2 content. Similarly, the refractive indices and absorption coefficients are tunable upon SiO2 incorporation. In-plane measurements of the magnetic properties of the CoFe2O4 films reveal a superparamagnetic behavior with both Co2+ and Fe3+ contributing to the magnetism. Polar Kerr measurements show the presence of a spontaneous magnetization in the CoFe2O4 and CoFe2O4-SiO2 (with SiO2 < 50 wt%) films, pointing to magnetic anisotropy perpendicular to the substrate. The origin of this effect is attributed to the constrained sintering conditions of the nano­particulate film and the negative magnetostriction of CoFe2O4.

We use frequency-resolved x-ray microscopy to fully characterize the potential well of a magnetic vortex in a soft ferromagnetic permalloy square. The vortex core is excited with magnetic broadband pulses and simultaneously displaced with a static magnetic field. We observe a frequency increase (blueshift) in the gyrotropic mode of the vortex core with increasing bias field. Supported by micromagnetic simulations, we show that this frequency increase is accompanied by internal deformation of the vortex core. The ability to modify the inner structure of the vortex core provides a mechanism to control the dynamics of magnetic vortices.

The synchrotron radiation facility ‘Solaris’ is currently being built in Krakow, Poland. The first experimental beamline at Solaris will use bending magnet radiation and two exchangeable end stations: a spectroscopic X-ray photoemission electron microscope and a soft X-ray absorption spectroscopy chamber. We present the beamline specifications and exemplary results obtained with our end station microscope, which (in statu nascendi of Solaris) has been operated at the NanoXAS beamline in the Swiss Light Source. The end stations should be available for a broad user community at Solaris in 2016. Copyright © 2015 John Wiley & Sons, Ltd.

Recent progress in the performance of polymer electronics devices has depended heavily on detailed knowledge of the properties of the active polymer materials. While many advanced conjugated polymer materials are being synthesized, the limited quantities produced severely restrict opportunities to measure their physical properties. In particular, the absolute mass density is a basic material property that impacts on many other important properties, yet it is very difficult to measure when in limited quantity. Here, we report a method to spatially resolve the absolute mass density of polymer materials at the nanoscale and measure values for polystyrene (1028 (43) kg/m3), PMMA (1140 (26) kg/m3), PFB (727 (51) kg/m3), and F8BT (749 (26) kg/m3). We estimate that the measurement method could be applied to sample quantities less than 1 picogram.

Spintronics evolves along new paths involving non-magnetic materials having large spin-obit coupling, typically 5d metals, allowing for example large spin-to-charge current conversion (spin Hall and Rashba-Edelstein effects). These heavy metals have other effects: in proximity of magnetic thin films they can burst out the Dzyaloshinskii-Moriya interaction leading to the stabilization of chiral magnetic structures. Another source of recent interest relies on “non-trivial topologies”, either of the band structure of the topological insulators, or of the spin textures in magnetic thin films. We will discuss our recent progress to control the topological textures known as skyrmions in multilayers made of heavy metals and magnetic layers. Aiming at using skyrmions as magnetic bits in “racetrack memory” structures, one of the present challenges is to efficiently move skyrmions with dimensions of a few tens of nanometers. The topology of these magnetic structures imposes peculiar dynamics, interesting both in fundamental and applied perspectives. Simulations indicate that spin-orbit torques, through the absorption of the spin current generated by a nearby layer, should be the most efficient method. The conducting surfaces of topological insulators at which the carriers’ spin and momentum are locked, can display better spin-to-charge conversion than what is found using heavy metals. However, the control of the interfaces is crucial to conserve the Dirac cone and the associated spin-momentum locking. We demonstrate by ARPES and spin pumping experiments how the properties of the α-Sn thin film topological insulator are preserved and can be used for spintronics, maybe to move skyrmions!

Ferromagnetic resonance (FMR) spectroscopy, x-ray magnetic circular dichroism (XMCD) spectroscopy and magnetic transmission soft x-ray microscopy (MTXM) experiments have been performed to gain insight into the magnetic anisotropy and domain structure of ultrathin Co | Ni multilayer films with a thin permalloy layer underneath. MTXM images with a spatial resolution better than 25 nm were obtained at the Co L3 edge down to an equivalent thickness of Co of only 1 nm, which establishes a new lower boundary on the sensitivity limit of MTXM. Domain sizes are shown to be strong functions of the anisotropy and thickness of the film.

The interplay between electronic eigenstates, spin, and orbital degrees of freedom, combined with fundamental breaking of symmetries is currently one of the most exciting fields of research. Multiferroics such as (GeMn)Te fulfill these requirements providing unusual physical properties due to the coexistence and coupling between ferromagnetic and ferroelectric order in one and the same system. Here we show that multiferroic (GeMn)Te inherits from its parent ferroelectric {\alpha}-GeTe compound a giant Rashba splitting of three-dimensional bulk states which competes with the Zeeman spin splitting induced by the magnetic exchange interactions. The collinear alignment of ferroelectric and ferromagnetic polarization leads to an opening of a tunable Zeeman gap of up to 100 meV around the Dirac point of the Rashba bands, coupled with a change in spin texture by entanglement of magnetic and spin-orbit order. Through applications of magnetic fields, we demonstrate manipulation of spin- texture by spin resolved photoemission experiments, which is also expected for electric fields based on the multiferroic coupling. The control of spin helicity of the bands and its locking to ferromagnetic and ferroelectric order opens fascinating new avenues for highly multifunctional multiferroic Rashba devices suited for reprogrammable logic and/or nonvolatile memory applications., Comment: 10 pages, 4 figures

Multiferroic composite materials combining ferroelectric and ferromagnetic order at room temperature have great potential for emerging applications such as four-state memories, magnetoelectric sensors, and microwave devices. In this paper, we report an effective and facile liquid phase deposition route to create multiferroic composite thin films involving the spin-coating of nanoparticle dispersions of BaTiO

International audience; Facing the ever-growing demand for data storage will most probably require a new paradigm. Nanoscale magnetic skyrmions are anticipated to solve this issue as they are arguably the smallest spin textures in magnetic thin films in nature. We designed cobalt-based multilayered thin films where the cobalt layer is sandwiched between two heavy metals providing additive interfacial Dzyaloshinskii-Moriya interactions, which reach a value close to 2 mJ m-2 in the case of the Ir|Co|Pt asymmetric multilayers. Using a magnetization-sensitive scanning x-ray transmission microscopy technique, we imaged small magnetic domains at very low field in these multilayers. The study of their behavior in perpendicular magnetic field allows us to conclude that they are actually magnetic skyrmions stabilized by the large Dzyaloshinskii-Moriya interaction. This discovery of stable sub-100 nm individual skyrmions at room temperature in a technologically relevant material opens the way for device applications in a near future.

The geometry of magnetic flux penetration in a high temperature superconductor at a buried interface was imaged using element-specific x-ray excited luminescence. We performed low temperature observation of the flux penetration in YBa2Cu3O7–δ (YBCO) at a buried interface by imaging of the perpendicular magnetization component in square Permalloy (Py) mesostructures patterned superjacent to a YBCO film. Element specific imaging below the critical temperature of YBCO reveals a cross-like geometry of the perpendicular magnetization component which is decorated by regions of alternating out-of-plane magnetization at the edges of the patterned Py structures. The cross structure can be attributed to the geometry of flux penetration originating from the superconductor and is reproduced using micromagnetic simulations. Our experimental method opens up possibilities for the investigation of flux penetration in superconductors at the nanoscale.

Magnetic skyrmions are arguably the smallest stable magnetic configuration in films, and therefore could be the ultimate magnetic storage bit [1,2]. They have also triggered a wide interest due to the new fundamental phenomena related to their topology. Numerical simulations have shown that the interfacial Dzyaloshinskii-Moriya interaction (DMI) can stabilize such skyrmions in nanoscale disks or tracks for a rather large range of DMI amplitudes for which the skyrmion can either be the ground state or metastable relative to the uniform state [4,5,6]. Here, we demonstrate experimentally the presence of skyrmions in metallic multilayers structures engineered to exhibit a strong DMI interaction.

Vortices are fundamental magnetic topological structures characterized by a curling magnetization around a highly stable nanometric core. The control of the polarization of this core and its gyration is key to the utilization of vortices in technological applications. So far polarization control has been achieved in single-material structures using magnetic fields, spin-polarized currents or spin waves. Here we demonstrate local control of the vortex core orientation in hybrid structures where the vortex in an in-plane Permalloy film coexists with out-of-plane maze domains in a Co/Pd multilayer. The vortex core reverses its polarization on crossing a maze domain boundary. This reversal is mediated by a pair of magnetic singularities, known as Bloch points, and leads to the transient formation of a three-dimensional magnetization structure: a Bloch core. The interaction between vortex and domain wall thus acts as a nanoscale switch for the vortex core polarization., Nature Communications, 6, ISSN:2041-1723

Simulations of magnetic microstructure in thin film elements used for programmable motion of magnetic particles

Synthesis and characterization of Sr0.75Y0.25C1-xMxO2.625+delta (M = Ga, 0.125

The domain configuration of micron-sized permalloy ellipses was studied under the influence of an in-plane rotating magnetic field using magnetic force microscopy. The field amplitude was chosen such that when the field is applied parallel to the long axis of the ellipses they are saturated, but when the field is perpendicular to the long axis they exhibit multi-domain states. The rotation angle for nucleation and annihilation of domains was determined for different magnitudes of the applied magnetic field and for two different lateral sizes of ellipses, 6 Am x 2 Am and 3 Am x 1 Am. It was found that both nucleation and annihilation occur over a range of angles for both lateral sizes of ellipses. Saturated states are stable for a wider range of angles for larger values of the applied field.

The sound of seagulls overhead greeted a diverse, international group of expert researchers in magnetism as they gathered on the shores of the Long Island Sound in late November. The group assembled on November 21–23, 2010, at Danford's Hotel and Marina in Port Jefferson, NY, USA, to participate in “MXLS10 - A Joint NSLS-II and MAX-lab Workshop: New Opportunities in Magnetism at Ultra-Low Emmittance Storage Rings.” With an idyllic setting on picturesque Port Jefferson Bay, adjacent to the terminal serving the lumbering ferries with their invigorating foghorns, the workshop brought together more than 40 scientists from Europe, Asia, and North America to hear about compelling and intriguing current research and discuss exciting opportunities afforded by the exceptional properties of the next-generation of X-ray storage rings: MAX-IV and NSLS-II.

The high-frequency dynamics of mode-coupled magnetic vortices have generated great interest for spintronic technologies, such as spin-torque nano-oscillators. While the spectroscopic characteristics of vortex oscillators have been reported, direct imaging of driven coupled magnetic quasi-particles is essential to the fundamental understanding of the dynamics involved. Here, we present the first direct imaging study of driven interlayer coaxial vortices in the dipolar- and indirect exchange-coupled regimes. Employing in situ high-frequency excitation with Lorentz microscopy, we directly observe the steady-state orbital amplitudes in real space with sub-5 nm spatial resolution. We discuss the unique frequency response of dipolar- and exchange-coupled vortex motion, wherein mode splitting and locking demonstrates large variations in coherent motion, as well as detail the resultant orbital amplitudes. This provides critical insights of the fundamental features of collective vortex-based microwave generators, such as their steady-state amplitudes, tunability and mode-coupled motion.

The influence of annealing time on an amorphous As cap layer and the depth distribution of Mn atoms have been investigated. The results show that a ∼1600 A thick As cap layer is completely desorbed after 3 h of annealing time. The depth distributions of Mn indicate that interstitial Mn atoms have diffused to the outer surface and being passivated. The thickness of the Mn passivation layer was around 90 A.

To address the amount of disorder and interface diffusion induced by annealing, all-Heusler multilayer structures, consisting of ferromagnetic Co2MnGe and nonmagnetic Rh2CuSn layers of varying thicknesses, have been investigated by means of hard x-ray photoelectron spectroscopy and x-ray magnetic circular dichroism. We find evidence for a 4 angstrom thick magnetically dead layer that, together with the identified interlayer diffusion, are likely reasons for the unexpectedly small magnetoresistance found for current-perpendicular-to-plane giant magnetoresistance devices based on this all-Heusler system. We find that diffusion begins already at comparably low temperatures between 200 and 250 degrees C, where Mn appears to be most prone to diffusion.

The internal phase profile of electromagnetic radiation determines many functional properties of metal, oxide or semiconductor heterostructures. In magnetic heterostructures, emerging spin electronic phenomena depend strongly upon the phase profile of the magnetic field H at gigahertz frequencies. Here we demonstrate nanometre-scale, layer-resolved detection of electromagnetic phase through the radio frequency magnetic field H(rf) in magnetic heterostructures. Time-resolved X-ray magnetic circular dichroism reveals the local phase of the radio frequency magnetic field acting on individual magnetizations M(i) through the susceptibility as M = χH(rf). An unexpectedly large phase variation, ~40°, is detected across spin-valve trilayers driven at 3 GHz. The results have implications for the identification of novel effects in spintronics and suggest general possibilities for electromagnetic-phase profile measurement in heterostructures.

We demonstrate in situ 90\ifmmode^\circ\else\textdegree\fi{} electric field-induced uniform magnetization rotation in single domain submicron ferromagnetic islands grown on a ferroelectric single crystal using x-ray photoemission electron microscopy. The experimental findings are well correlated with micromagnetic simulations, showing that the reorientation occurs by the strain-induced magnetoelectric interaction between the ferromagnetic nanostructures and the ferroelectric crystal. Specifically, the ferroelectric domain structure plays a key role in determining the response of the structure to the applied electric field, resulting in three strain-induced regimes of magnetization behavior for the single domain islands.

Current induced domain wall (DW) depinning of a narrow DW in out-of-plane magnetized (Pt/Co)_{3}/Pt multilayer elements is studied by magnetotransport. We find that for conventional measurements Joule heating effects conceal the real spin torque efficiency and so we use a measurement scheme at a constant sample temperature to unambiguously extract the spin torque contribution. From the variation of the depinning magnetic field with the current pulse amplitude we directly deduce the large nonadiabaticity factor in this material and we find that its amplitude is consistent with a momentum transfer mechanism.

A magnetic vortex domain wall, confined in a Permalloy nanowire with periodically varying width, is brought to resonance and long-range motion by means of a spin-polarized alternating current in mi ...

We report on the experimental realization of tetragonal Fe-Co alloys as a constituent of Fe0.36Co0.64/Pt superlattices with huge perpendicular magnetocrystalline anisotropy energy, reaching 210µeV/atom, and a saturation magnetization of 2.5µB/atom at 40 K, in qualitative agreement with theoretical predictions. At room temperature the corresponding values 150µeV/atom and 2.2µB/atom are achieved. This suggests that Fe-Co alloys with carefully chosen combinations of composition and distortion are good candidates for high-density perpendicular storage materials. © 2006 The American Physical Society.

The influence of annealing parameters - temperature and time - on the magnetic properties of As-capped (Ga,Mn)As epitaxial thin films have been investigated. The dependence of the transition temperature (Tc) on annealing time marks out two regions. The Tc peak behavior, characteristic of the first region, is more pronounced for thick samples, while for the second (`saturated') region the effect of the annealing time is more pronounced for thin samples. A right choice of the passivation medium, growth conditions along with optimal annealing parameters routinely yield Tc-values of ~ 150 K and above, regardless of the thickness of the epilayers., 5 pages, 3 figures

Magnetic vortices in nanoscopic ferromagnetic elements can be treated as solitons that exhibit static and dynamic stability even above room temperature, making them promising for technological applications. Although their properties at low energy configurations have been well studied, the properties of solitons undergoing structural breakdown are poorly understood. Here, we destabilize the soliton through Zeeman and demagnetization interactions and investigate the symmetry breaking of the magnetic vortex state. Using high-resolution Lorentz imaging and numerical simulations, we observe phase transitions of the core from the characteristic point-like structure into distinct extended asymmetric states differentiated by the polarity. The deformations start at intermediate displacements and are traced until the point of annihilation at the disc's edge. We discuss the use of these asymmetric states as a method to determine the core polarity for in-plane magnetic imaging techniques.

We have investigated the magnetic anisotropy and interlayer coupling in trilayer films of permendur(100 \AA)/Ru/permalloy(100 \AA), with the thickness of the Ru spacer varying from 0 to 200 \AA. Wh ...

We present time-and element-resolved measurements of the magnetization dynamics in a ferromagnetic trilayer structure. A pump-probe scheme was utilized with a microwave magnetic excitation field ph ...

The pinning properties of magnetic vortex domain walls were experimentally investigated in patterned nanowires with artificial constrictions. Domain walls were nucleated and depinned by applied mag ...

The magnetic properties of tetragonally strained Fe0.36Co0.64 alloys in the form of FeCo/Pt(001) superlattices have been investigated experimentally. The strain was controlled by varying the indivi ...