Search

Two-dimensional (2D) Rashba systems have been intensively studied in the last decade due to their unconventional physics, tunability capabilities, and potential for spin-charge interconversion when compared to conventional heavy metals. With the advent of a new generation of spin-based logic and memory devices, the search for Rashba systems with more robust and larger conversion efficiencies is expanding. Conventionally, demanding techniques such as angle- and spin-resolved photoemission spectroscopy are required to determine the Rashba parameter $\alpha_{R}$ that characterizes these systems. Here, we introduce a simple method that allows a quantitative extraction of $\alpha_{R}$, through the analysis of the bilinear response of angle-dependent magnetotransport experiments. This method is based on the modulation of the Rashba-split bands under a rotating in-plane magnetic field. We show that our method is able to correctly yield the value of $\alpha_{R}$ for a wide range of Fermi energies in the 2D electron gas at the LaAlO$_{3}$/SrTiO$_{3}$ interface. By applying a gate voltage, we observe a maximum $\alpha_{R}$ in the region of the band structure where interband effects maximize the Rashba effect, consistently with theoretical predictions.

Magnetic skyrmions are nanoscale windings of the spin configuration that hold great promise for technology due to their topology-related properties and extremely reduced sizes. After the recent observation at room temperature of sub-100 nm skyrmions stabilized by interfacial chiral interaction in magnetic multilayers, several pending questions remain to be solved, notably about the means to nucleate individual compact skyrmions or the exact nature of their motion. In this study, a method leading to the formation of magnetic skyrmions in a micrometer-sized nanotrack using homogeneous current injection is evidenced. Spin-transfer-induced motion of these small electricalcurrent-generated skyrmions is then demonstrated and the role of the out-of-plane magnetic field in the stabilization of the moving skyrmions is also analysed. The results of these experimental observations of spin torque induced motion are compared to micromagnetic simulations reproducing a granular type, non-uniform magnetic multilayer, in order to address the particularly important role of the magnetic inhomogeneities on the current-induced motion of sub-100 nm skyrmions, for which the material grains size is comparable to the skyrmion diameter., 11 pages, 5 figures

Since the discovery of ferromagnetic two-dimensional (2D) van der Waals (vdW) crystals, significant interest on such 2D magnets has emerged, inspired by their appealing properties and integration with other 2D family for unique heterostructures. In known 2D magnets, spin-orbit coupling (SOC) stabilizes perpendicular magnetic anisotropy (PMA). Such a strong SOC could also lift the chiral degeneracy, leading to the formation of topological magnetic textures such as skyrmions through the Dzyaloshinskii-Moriya interaction (DMI). Here, we report the experimental observation of N\'eel-type chiral magnetic skyrmions and their lattice (SkX) formation in a vdW ferromagnet Fe3GeTe2 (FGT). We demonstrate the ability to drive individual skyrmion by short current pulses along a vdW heterostructure, FGT/h-BN, as highly required for any skyrmion-based spintronic device. Using first principle calculations supported by experiments, we unveil the origin of DMI being the interfaces with oxides, which then allows us to engineer vdW heterostructures for desired chiral states. Our finding opens the door to topological spin textures in the 2D vdW magnet and their potential device application., Comment: 26 pages, 5 figures

Controlling the motion of magnetic domain walls (DWs) in ultrathin films with perpendicular magnetic anisotropy (PMA) has opened perspectives for mass-storage applications such as ``racetrack memory''. However, a crucial issue for this technology is to efficiently move and store domain walls along very narrow wires. The authors' approach uses prepatterned substrates with regularly spaced nanoscale steps to grow high-quality films with PMA. The very low steps act as efficient pinning sites when DWs move $a\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}s$ them, yet as very efficient conduits when DWs move $a\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}g$ them. This may be a promising solution to crucial problems concerning edge damage at very small wire dimensions.

We analyze the opportunity of inserting a Ta layer between the polarizing section and the high anisotropy section in the reference subsystem of CoFeB-based tunnel junctions with perpendicular magnetic anisotropy. Using vector network analyzer ferromagnetic resonance, polar Kerr magnetometry, and magnetization dynamics modeling, we deduce the strength of the ferromagnetic interlayer exchange coupling energy J through various thickness of tantalum that impacts on the overall performance of the tunnel junctions. J culminates at 0.44 mJ/m 2 through 3 A of Ta, but the Co/Pt properties are then suboptimal. Our methodology can be used to rationally find the performance optimum in the reference layers of perpendicularly magnetized tunnel junctions.

While ferromagnets are at the heart of daily life applications, their large magnetization and resulting energy cost for switching bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem and often possess remarkable extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or produce emergent spin-orbit effects, which enable efficient spin-charge interconversion. To harness these unique traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive scanning nanomagnetometer based on a single nitrogen-vacancy (NV) defect in diamond, we demonstrate the first real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film, at room temperature. We image the spin cycloid of a multiferroic BiFeO$_3$ thin film and extract a period of $\sim70$ nm, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO$_3$ to manipulate the cycloid propagation direction by an electric field. Besides highlighting the unique potential of NV magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO$_3$ can be used as a versatile platform for the design of reconfigurable nanoscale spin textures.

International audience; Sub-100-nm skyrmions are stabilized in magnetic metallic multilayers and observed using transmission electron microscopy, magnetic force microscopy, scanning transmission X-ray microscopy and X-ray resonant magnetic scattering. All these advanced imaging techniques demonstrate the presence of "pure" Néel skyrmion textures with a determined chirality. Combining these observations with electrical measurements allows us to demonstrate reproducible skyrmion nucleation using current pulses, and measure their contribution to the transverse resistivity to detect them electrically. Once nucleated, skyrmions can be moved using charge currents. We find predominantly a creep-like regime, characterized by disordered skyrmion motion, as observed by atomic force microscopy and scanning transmission X-ray microscopy. These observations are explained qualitatively and to some extent quantitatively by the presence of crystalline grains of about 20 nm lateral size with a distribution of magnetic properties.

Observing jumping domain walls Domain walls, which separate regions of opposite magnetization in a ferromagnet, have rich dynamics that are difficult to characterize in small samples. Tetienne et al. imaged the magnetization of a thin ferromagnetic wire and observed the jumping of a domain wall between different positions along the wire. They used a scanning magnetic microscope based on a defect in diamond. The laser light needed to operate the microscope also enabled the control of the domain wall motion by causing local heating, which made the illuminated position more likely to contain a domain wall. Science , this issue p. 1366

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!

The Dzyaloshinskii-Moriya Interaction (DMI) has recently attracted considerable interest owing to its fundamental role in the stabilization of chiral spin textures in ultrathin ferromagnets, which are interesting candidates for novel spintronic technologies. Here, the authors present an experimental study of the DMI strength that is induced in nanometer-thick CoFeB ferromagnetic thin films in contact with different nonmagnetic metal underlayers. They use a novel technique for noninvasive high-sensitivity sensing of magnetic field: a scanning nanomagnetometer based on the magnetic response of a single nitrogen-vacancy defect in diamond. The magnetic domain walls are mapped, the spin structure and type of domain wall determined, and the DMI strength extracted. Importantly, the authors find local variation of the DMI constant, which clearly suggests that local field mapping techniques are extremely important to study this physics.

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 stratigraphy at Oje, central Sweden, has been reinvestigated. Till-covered organic sediments were encountered in two out of three excavations, while in one excavation only till occurred. One sediment succession was analysed for pollen and macrofossils. The vegetation represented by both pollen and macrofossil flora indicates a correlation with (the latter) part of the Holsteinian Interglacial, also in accordance with the predominantly acidophilous diatom flora.

The till-covered organic sediments at Harnosand have been resampled and reinvestigated with respect to their micro- and macrofossil content. The sediments were deposited in a shallow freshwater basin with a sandy substratum and probably under oligotrophic conditions. The regional vegetation consisted of a shrub or herb tundra, later changing into an open Betula forest with scattered Picea and Larix. In the lake, submerged plants such as Potamogeton filiformis and Isoetes lacustris grew, together with Carex. On the shores the vegetation consisted of Betula nana, occasional Betula trees, Salix and Selaginella selaginoides. The beetle fauna suggests an average July temperature of 10–11°C. The flora indicates limited leaching and, thus, deposition during a relatively long and warm interstadial is suggested. The Harnosand sediments are subsequently correlated with the Brorup Interstadial.

Till-covered sand and silt sediments with organic material from Boliden, northern Sweden, have been resampled and reinvestigated. Texture and petrographic analyses demonstrated one till bed overlying, and one underlying the sandy sediments. Low frequencies of diatoms were noted, representing freshwater, halophilous and brackish water taxa. The diatoms may be allochthonous or autochthonous, or redeposited from older deposits. Pollen analysis revealed a new picture of the composition of the vegetation, as compared with earlier investigations. The flora consisted of an arctic-subarctic treeless shrub and herb vegetation dominated by Salix, Betula nana, Gramineae and Cyperaceae. Artemisia and several arctic-alpine herbs were important elements. The identification of Salix wood as well as fruits and fruit scales of Betula nana and Betula cf. humilis is in agreement with the pollen-analytical results, as is the occurrence of Nordicboreal species of Coleoptera. Two radiocarbon datings resulted in an age of c. 45,000 B. P. and >40,000 B.P. The Boliden till-covered sediments were most probably deposited during an Early or Middle Weichselian interstadial, but the initial or final stage of an interglacial (Eemian) is also possible.

We present a new approach to infer the surface density of magnetic moments $I_s$ in ultrathin ferromagnetic films with perpendicular anisotropy. It relies on quantitative stray field measurements with an atomic-size magnetometer based on the nitrogen-vacancy center in diamond. The method is applied to microstructures patterned in a 1-nm-thick film of CoFeB. We report measurements of $I_s$ with a few percent uncertainty and a spatial resolution in the range of $(100$ nm)$^2$, an improvement by several orders of magnitude over existing methods. As an example of application, we measure the modifications of $I_s$ induced by local irradiation with He$^+$ ions in an ultrathin ferromagnetic wire. This method offers a new route to study variations of magnetic properties at the nanoscale., Comment: 9 pages and 7 figures including main text and Supplemental Information

Electric field effect (EFE) in ferromagnetic/oxide dielectric structures provides a new route to control domain wall (DW) dynamics with low power dissipation. However, EFE on DW velocity has been only observed so far in the creep regime where DW velocity is low due to a strong interaction with pinning sites. Our approach makes use of CoFeB-MgO films with perpendicular magnetic anisotropy (PMA), which are considered as the most promising not only for STT-RAM but also for DW based memories, since a combination of spin Hall effect and Dzyaloshinskii-Moriya interaction could lead to efficient DW motion under current. Using NV center microscopy to map DW pinning along a magnetic wire, we first show1 that Ta/Co 40 Fe 40 B 20 (1nm)/MgO structures exhibit a very low density of pinning defects with respect to others materials with PMA. Then we show2 gate voltage modulation of DW velocity from the creep to the flow regime with velocities up to 20 m s−1. We demonstrate a universal description of EFE over the full range of DW dynamics by taking into account an effective magnetic field being linear with the electric field. In addition to our previous approach of using strain3, this work opens new opportunities for the study and optimization of electric field effect at ferromagnetic metal/insulator interfaces.

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.

We report field- and current-induced domain wall (DW) depinning experiments in Ta/Co20Fe60B20/MgO nanowires through a Hall cross geometry. While purely field-induced depinning shows no angular dependence on in-plane fields, the effect of the current depends crucially on the internal DW structure, which we manipulate by an external magnetic in-plane field. We show for the first time depinning measurements for a current sent parallel to the DW and compare its depinning efficiency with the conventional case of current flowing perpendicularly to the DW. We find that the maximum efficiency is similar for both current directions within the error bars, which is in line with a dominating damping-like spin-orbit torque (SOT) and indicates that no large additional torques arise for currents parallel to the DW. Finally, we find a varying dependence of the maximum depinning efficiency angle for different DWs and pinning levels. This emphasizes the importance of our full angular scans compared to previously used measurements for just two field directions (parallel and perpendicular to the DW) and shows the sensitivity of the spin-orbit torque to the precise DW structure and pinning sites., Comment: 11 pages, 3 figures

The penetration depth of the skin-effect has been calculated for a specimen in the form of a piece of amorphous glass-coated magnetic micro-wire of the “non-magnetostrictive” composition Co67Fe3.85Ni1.45Mo1.7Si14.5B11.5 displaying large GMI effect. For these calculations a simple model was applied in which a rough assumption was made that the changes of the real component of the impedance are due only to changes in the effective cross-section of the wire for the AC-current. The evolution of the penetration depth with the applied DC-axial field and frequencies of the AC-current, flowing along the wire, is presented. The so-called Cole–Cole diagrams were also plotted for the same specimen. These diagrams, representing the measured impedance plotted in the complex plane, were obtained for axial DC-magnetic field of selected intensities and circular AC-field generated by an AC-current of various frequencies (1–30 MHz) flowing along the wire specimen. Analysis of the diagrams enabled one to characterize magnetization processes within the wire specimen and also to estimate the median relaxation time of these processes as well as a relative measure of the distribution of relaxation times.

Amorphous magnetic microwires are novel materials, which are characterized by the unique magnetic properties. Their magnetization process runs through the depining and subsequent propagation of the single-domain wall. This allows us to study the magnetization processes of the single-domain wall either in static (when the domain wall lies in its potential) or dynamic (when the domain wall propagates along the wire) mode. In the given work, we present surprising results that were found during the single-domain wall switching and propagation in microwires. The negative critical propagation field during the propagation of the single-domain wall in microwires has been found. Moreover, new contribution (based on the structural relaxation) to the domain wall damping during its propagation in microwire was found. The complex shape of the single-domain wall potential, which consists of two contributions, has been found in microwires. The magnetoelastic one coming from the magnetoelastic interaction of the domain wall with the stresses applied on microwires and the stresses introduced during the microwire's production and stabilization one coming from the structural relaxation on atomic level.

Electric field effects in ferromagnetic metal/dielectric structures provide a new route to control domain wall dynamics with low-power dissipation. However, electric field effects on domain wall velocities have only been observed so far in the creep regime where domain wall velocities are low due to strong interactions with pinning sites. Here we show gate voltage modulation of domain wall velocities ranging from the creep to the flow regime in Ta/Co40Fe40B20/MgO/TiO2 structures with perpendicular magnetic anisotropy. We demonstrate a universal description of the role of applied electric fields in the various pinning-dependent regimes by taking into account an effective magnetic field being linear with the electric field. In addition, the electric field effect is found to change sign in the Walker regime. Our results are consistent with voltage-induced modification of magnetic anisotropy. Our work opens new opportunities for the study and optimization of electric field effect at ferromagnetic metal/insulator interfaces., Domain walls in ferromagnetic–oxide structures can be moved using an electric field, which could be useful for low-power electronic devices. Here, the authors demonstrate the modulation of the velocity of these domain walls between a creep and a flow regime.

The penetration depth of the skin-effect and circumferential permeability have been calculated for a magnetic micro-wire of the nominal composition Co67Fe3.85Ni1.45Mo1.7Si14.5B11.5 displaying large giant magnetoimpedance (GMI) effect. For these calculations a simple model was applied in which a rough assumption was made that the changes of the real component of the impedance are due only to changes in the effective cross-section of the wire for the AC-current. The evolution of both, the penetration depth and circumferential permeability, is presented as a function of the applied DC-axial field at various frequencies of the AC-current, flowing along the wire. These quantities are calculated using the experimental data of the real component of the micro-wire impedance. A comparison of the experimental data obtained for the imaginary component of the impedance with those calculated by the model, shows that the latter gives only a qualitative agreement with the measured dependencies.

The temperature dependence of the magnetic behaviour of Fe-based glass-coated amorphous microwires with positive and large magnetostriction constant (around 30 ppm at room temperature) has been studied in the temperature range from 2 to 390 K. For long enough microwires (about 10 mm), hysteresis loops are squared shaped denoting the existence of a single domain structure and the magnetization reversal by a single Barkhausen jump. In the case of short microwires (around 2 mm) drastic changes are observed at low temperature where such magnetic bistability is lost. This is interpreted considering the influence of shape anisotropy: for short wires the demagnetizing field becomes large enough to destroy the single domain structure. On the other hand, the changing magnetoelastic anisotropy induced by coating when reducing measuring temperature is also considered. Particular emphasis is additionally done to study the dependence of the switching field for magnetization reversal and that of its fluctuations on temperature and frequency of exciting field.

The temperature dependence of the switching field distribution has been studied. Two main contributions to the coercivity of the magnetic microwires were found: (i) magnetoelastic pinning of the domain wall, and (ii) pinning of the domain wall on the atomic level defect. The thermally activated mechanism model has been used to describe the switching field distribution. This model gives us the possibility to describe the change of the switching field distribution with temperature and time: its shape and the amplitude of average value. It is shown that the switching field distribution is sensitive to the shape of the bottom of the potential well of the domain wall, whereas the position of the distribution depends on the shape of the domain wall potential at its inflection points. Finally, stabilisation experiments have been done to proof the thermo-activated mechanism model validity.

Magnetostrictive microwires exhibit bistable magnetic behavior characterized by square hysteresis loops, a consequence of the magnetization reversal by depinning of a single domain wall from the closure structure at one end of the wire. This bistable behavior spontaneously observed in magnetostrictive microwires has been previously thoroughly studied at room temperature. In the present work, the temperature dependence of the remagnetization process is investigated in magnetic microwires, a few micrometres in diameter, covered by glassy coating plus additional metallic coatings. The influence first of geometrical parameters as length and diameter is considered. Later on, an emphasis is placed on the influence of the Pyrex and additional sputtered and electroplated coatings on the temperature dependence of switching field. Bistability can be lost, depending on the character of the coating, when reducing the measuring temperature due to the thermally induced anisotropy arising from the differential thermal expansion coefficient of the composite wire. On the other hand, the temperature dependence of the switching field and its distribution function have been measured. It is shown that the switching field increases as temperature decreases, which is analyzed considering the thermally activated pinning mechanism and the magnetostrictive contribution.

Co 79.6 Fe 4.6 Si 9.2 B 2.7 Mo 3.9 fibers have been produced by the modified process of melt-extraction. Hysteresis loop, magnetostriction constant, λ s and giant magneto-impedance (GMI) ratio (total impedance, real and imaginary contributions) of such fibers have been measured. Studied fibers exhibit excellent magnetic softness (coercivity about 20 A m −1 ), small positive magnetostriction constant ( λ s ≈1.13×10 −6 ) and GMI ratio of the order of 50% in as-cast state. Current annealing has been employed to tailor the magnetic properties and GMI effect of these fibers.

The dependence of magnetoimpedance ratio, ΔZ/Z = {[Z(H)-Z(Hmax)]/Z(Hmax)}.100%, on the axial magnetic field of soft magnetic Co67Fe3.85Ni1.45B11.5Si14.5Mo1.7glass coated amorphous microwires has been investigated in the frequency range 1 - 30 MHz, for the driving current amplitudes 0.75 - 5 mA, and at the maximum axial DC-field of 8 kA/m. In the as-prepared sample, maximum GMI ratio, ΔZ/Zmax≈380%, has been observed at the highest used frequency (30 MHz). It has, however, been shown, that Joule heating enables to enlarge the ΔZ/Zmax ratio up to 500%. A strong dependence of ΔZ/Zmax on annealing time, frequency and amplitude of the driving current has also been observed. The results of the GMI measurements, presented as a function of the annealing time with the frequency and current amplitude as the parameters, showed an increase of the anisotropy field with an increase of the annealing time and temperature. The observed dependencies have been interpreted in terms of stress relaxation and changes of the magneto-elastic anisotropy induced by the Joule heating.

The recent observation of current-induced domain wall (DW) motion with large velocity in ultrathin magnetic wires has opened new opportunities for spintronic devices. However, there is still no consensus on the underlying mechanisms of DW motion. Key to this debate is the DW structure, which can be of Bloch or N\'eel type, and dramatically affects the efficiency of the different proposed mechanisms. To date, most experiments aiming to address this question have relied on deducing the DW structure and chirality from its motion under additional in-plane applied fields, which is indirect and involves strong assumptions on its dynamics. Here we introduce a general method enabling direct, in situ, determination of the DW structure in ultrathin ferromagnets. It relies on local measurements of the stray field distribution above the DW using a scanning nanomagnetometer based on the Nitrogen-Vacancy defect in diamond. We first apply the method to a Ta/Co40Fe40B20(1 nm)/MgO magnetic wire and find clear signature of pure Bloch DWs. In contrast, we observe left-handed N\'eel DWs in a Pt/Co(0.6 nm)/AlOx wire, providing direct evidence for the presence of a sizable Dzyaloshinskii-Moriya interaction (DMI) at the Pt/Co interface. This method offers a new path for exploring interfacial DMI in ultrathin ferromagnets and elucidating the physics of DW motion under current., Comment: Main text and Supplementary Information, 33 pages and 12 figures

Lumps of diatom-rich, laminated sediments were discovered redeposited and interbedded in a Late Weichselian delta sequence in a small glaciofluvial esker at Snickarekullen, south-western Sweden. Radiocarbon dating of the sediments gave an infinite age (≫45 000 B.P.). The composition and sediment structure of the lumps were studied in epoxy-impregnated thin sections using SEM and EDS. Quantitative and qualitative diatom analyses of the sediments were carried out, as well as pollen and macrofossils analyses. The biostratigraphy is compared with that from Holsteinian interglacial sites in surrounding countries, the evidence for which is briefly reviewed. It is concluded that the sediments were deposited in the central part of a lake probably during different parts of the Holsteinian interglacial. The water body changed from a rather shallow lake with a high pH to a considerably deeper, oligotrophic lake with neutral to slightly acidic water during the sedimentation period. The local and regional vegetation developed from an open pine-birch forest into a much more closed vegetation of pine, spruce, larch, alder and hornbeam.

The results of ferromagnetic resonance (FMR) investigation of the amorphous glass-coated microwires with different internal stresses are reported. The internal stresses determine the shift of the resonance field position indicating the magnetoelastic anisotropy as the origin of the magnetic anisotropy of the wire surface region. The values of the magnetoelastic anisotropy field calculated on the basis of the theory of viscoelasticity are also presented.

The main aim of this study has been to examine the possibility of using spectral signature measurements to separate till beds. Spectral reflectances of six till samples from two sites were recorded using an advanced reflectometer in the wavelength region 0.4 to 2.3 μm. Two grain-size fractions (0.074 and 0.125 mm) were selected for the spectral analyses. Colour analysis of the samples using the Munsell Soil Color Chart was also made. The till samples investigated were difficult to separate from each other using standard methods, but can now be differentiated as units with the help of spectral signatures and colour analysis. Spectral signature measurement of tills can, however, be a more reliable way of separating till units than the Munsell analysis.

The temperature dependence of the switching field and its fluctuations for a bistable Fe-based glass coated microwires family with magnetostriction values from 2/spl times/10/sup -6/ to 28/spl times/10/sup -6/ is presented in the temperature range 77-425 K. A simple model considering two energy contributions from magnetoelastic pinning and structural relaxation is considered to fit experimental data. Particularly, the contribution of magnetostriction and coating stresses to the temperature dependence of magnetoelastic term is analyzed in more detail. The relative magnetoelastic contribution is shown to increase with Fe content as magnetostriction increases, as well as with temperature. The contributions to magnetostriction from single-ion and two-ion mechanisms are also analyzed.

The switching field distribution for magnetization reversal in a single Barkhausen jump of a bistable Fe-based amorphous microwire as well as its temperature dependence have been investigated in the temperature range from 77 to 450 K. Two processes have been identified to be responsible for the temperature dependence of the switching field: magnetostrictive volume domain wall pinning on stresses and relaxation effects due to local structural rearrangements. While at low temperatures, pinning on the atomic level defects plays the dominant role, magnetostrictive pinning becomes more important at intermediate temperatures. A simple model is proposed considering both energy contributions that fits reasonably well with experimental data and allows us to interpret additionally the observed temperature dependence of the switching field fluctuations.

A detailed study of the complex inductance response of as-cast CoFeBSi wires as a function of frequency (100 Hz–13 MHz range) and circular field amplitude [0.1–17 A/m room mean square (rms) on the surface of the wire] in the giant magnetoimpedance arrangement is presented. The analysis of experimental results show evidence of magnetization processes associated with circumferential domain walls, such as domain wall pinning, bulging, and displacement. The unpinning field was measured as 0.2 A/m (rms) at 5 kHz. It is shown that the analysis of spectroscopic plots of real and imaginary inductance leads to characterization of the magnetization process involved.

The stratigraphy of a sediment sequence at the Leveaniemi open mine includes two tills resting on weathered bedrock, covered by silty/sandy waterlain sediments. All these sediments are overlain by one till. The tills over- and underlying the sorted sediments show a pollen flora dominated by Betula nana-type pollen together with herbs, mostly Graminae. Pollen analyses of a silty sequence of the waterlain sediments show a pollen flora completely dominated by Betula nana, with a herbaceous pollen flora, represented by, above all, Graminae and Cyperaceae. Less than 2% Pinus pollen were registered. Thermoluminescence dating of three samples gave a mean age of 121,000 years BP. The sorted sediments are interpreted as having been deposited during an Early Weichselian interstadial, either the Brorup or the Odderade Interstadial.

We explore the influence of the top electrode materials (W, Co, Ni, Ir) on the electronic band profile in ferroelectric tunnel junctions based on super-tetragonal BiFeO3. Large variations of the transport properties are observed at room temperature. In particular, the analysis of current vs. voltage curves by a direct tunneling model indicates that the metal/ferroelectric interfacial barrier height increases with the top-electrode work function. While larger metal work functions result in larger OFF/ON ratios, they also produce a large internal electric field which results in large and potentially destructive switching voltages.

The domain wall dynamics during magnetization reversal process of glass-coated amorphous Fe77.5Si7.5B15 bistable microwire was considered. Its domain structure deriving from the magnetoelastic and shape anisotropies consists of an axial single domain and two closure domain structures at the ends, plus an outer radial-helical shell in its surface. This articles report the measured domain wall velocities, mobilities, and shape, which enables the determination of the domain wall energy per unit area, g, from direct observations of the domain wall length, L.

Parte del número especial: Proceedings of the Joint European Magnetic Symposia (JEMS' 04) A novel technique involving combined sputtering and electroplating procedures has been recently developed to deposit metallic (magnetic or not) nano and microlayer tubes onto glass-coated amorphous magnetic microwires to enable the tailoring of their magnetic behavior. Here, after introducing the general aspects of that technique, we present the latest results on a new family of two-phase magnetic samples: bi-magnetic multilayer microwires. They consist of a magnetically soft nucleus (typically a Fe or Co base amorphous microwire, coated by Pyrex layer) onto which a 30 nm thick Au layer is first sputtered followed by the electroplating of a harder microlayer, namely CoxNi(1−x) layer, with x controlled by the current density during electrodeposition whose micrometric thickness is also controlled by plating time. The hysteresis loops present a two-step reversal process typical of two-phase magnetic material. The magnetization reversal of the soft nucleus and the harder layer takes place at around 1 Oe and up to about 200 Oe, respectively. The presence of sputtered and electroplated layers induces significant stresses in the soft magnetic nucleus that modify its magnetization easy axis. This technique allowing us the tailoring of the magnetic behavior of multilayer magnetic microwires opens new possibilities for applying these novel materials as sensing elements in various devices.

The mechanism of nucleation and propagation of a single-domain wall is studied as a function of temperature in bistable Fe-based amorphous microwire with a unique simple domain structure. An extended nucleation-propagation model is proposed with a negative nucleation field. From quantitative analysis of the propagating wall characteristics, a new damping is theoretically introduced as arising from structural relaxation which dominates in the low temperature regime.

We studied state of the art perpendicularly magnetized tunnel junctions to identify performance improvement opportunities. The free layer has both a low damping and a large anisotropy. Conversely, the perpendicular remanence of the reference layer requires its encapsulation and its coupling with the hard layer. The weak pinning and low damping of the reference layer may make it prone to fluctuations induced by spin-torque. The combined optimization of the interface anisotropies on both sides of the MgO, together with the reproducibility of the interlayer exchange coupling are the main material challenges for our type of magnetic tunnel junctions.

We have studied the domain-wall dynamics in Ta-CoFeB-MgO ultra-thin films with perpendicular magnetic anisotropy for various Co and Fe concentrations in both the amorphous and crystalline states. We observe three motion regimes with increasing magnetic field, which are consistent with a low fields creep, transitory depinning, and high fields Walker wall motion. The depinning fields are found to be as low as 2 mT, which is significantly lower than the values typically observed in 3d ferromagnetic metal films with perpendicular magnetic anisotropy. This work highlights a path toward advanced spintronics devices based on weak random pinning in perpendicular CoFeB films.

We study perpendicularly magnetized Ta/CoFeB/MgO films and investigate whether their irradiation with light ions can improve their properties by inducing a different crystallization dynamics. We report the magnetization, anisotropy, g-factor, and damping dependence upon irradiation fluence and discuss their evolutions with collisional mixing simulations and its expected consequence on magnetic properties. We show that after a short irradiation at 100 °C, the anisotropy increases close to the value obtained by conventional high temperature annealing. Higher irradiation-induced increase of anisotropy can be obtained but with a detrimental effect on the damping that can be understood from spin-orbit contributions.

The dynamics of a single domain wall in finite glass-coated microwires is reported in the low-field regime below the switching field. The power law of the single domain wall propagating over a large distance is confirmed. Three regions are determined for the propagating domain wall. Below some critical field, H0, the domain wall is pinned at the wire's end. Just above that critical field, the wall moves in the adiabatic regime, interacting with the defects during its propagation, with an average velocity of v = S'(H−H0)β. At high field, the domain wall propagates in the viscous regime and its average velocity is proportional to the applied magnetic field, H. An analysis of the temperature dependence of the scaling factor β is further reported. It is also shown that the domain wall mobility parameter S' is field-independent and is proportional to the domain wall mobility S in the viscous regime.