Magnetic skyrmions are topologically nontrivial particles with a potential application as information elements in future spintronic device architectures. While they are commonly portrayed as two ...dimensional objects, in reality magnetic skyrmions are thought to exist as elongated, tube-like objects extending through the thickness of the host material. The study of this skyrmion tube state (SkT) is vital for furthering the understanding of skyrmion formation and dynamics for future applications. However, direct experimental imaging of skyrmion tubes has yet to be reported. Here, we demonstrate the real-space observation of skyrmion tubes in a lamella of FeGe using resonant magnetic x-ray imaging and comparative micromagnetic simulations, confirming their extended structure. The formation of these structures at the edge of the sample highlights the importance of confinement and edge effects in the stabilisation of the SkT state, opening the door to further investigation into this unexplored dimension of the skyrmion spin texture.
In the emerging field of magnonics, spin waves are foreseen as signal carriers for future spintronic information processing and communication devices, owing to both the very low power losses and a ...high device miniaturization potential predicted for short-wavelength spin waves. Yet, the efficient excitation and controlled propagation of nanoscale spin waves remains a severe challenge. Here, we report the observation of high-amplitude, ultrashort dipole-exchange spin waves (down to 80 nm wavelength at 10 GHz frequency) in a ferromagnetic single layer system, coherently excited by the driven dynamics of a spin vortex core. We used time-resolved x-ray microscopy to directly image such propagating spin waves and their excitation over a wide range of frequencies. By further analysis, we found that these waves exhibit a heterosymmetric mode profile, involving regions with anti-Larmor precession sense and purely linear magnetic oscillation. In particular, this mode profile consists of dynamic vortices with laterally alternating helicity, leading to a partial magnetic flux closure over the film thickness, which is explained by a strong and unexpected mode hybridization. This spin-wave phenomenon observed is a general effect inherent to the dynamics of sufficiently thick ferromagnetic single layer films, independent of the specific excitation method employed.
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Reduced dimensionality and symmetry breaking at interfaces lead to unusual local magnetic configurations, such as glassy behavior, frustration or increased anisotropy. The interface between a ...ferromagnet and an antiferromagnet is such an example for enhanced symmetry breaking. Here we present detailed X-ray magnetic circular dichroism and X-ray resonant magnetic reflectometry investigations on the spectroscopic nature of uncompensated pinned magnetic moments in the antiferromagnetic layer of a typical exchange bias system. Unexpectedly, the pinned moments exhibit nearly pure orbital moment character. This strong orbital pinning mechanism has not been observed so far and is not discussed in literature regarding any theory for local magnetocrystalline anisotropy energies in magnetic systems. To verify this new phenomenon we investigated the effect at different temperatures. We provide a simple model discussing the observed pure orbital moments, based on rotatable spin magnetic moments and pinned orbital moments on the same atom. This unexpected observation leads to a concept for a new type of anisotropy energy.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Miniature magnetic sensors based on magnetoplasmonic crystals (MPlCs) exhibit high sensitivity and high spatial resolution, which can be obtained by the excitation of surface plasmon polaritons. A ...field dependence of surface plasmon polaritons' enhanced magneto-optical response strongly correlates with magnetic properties of MPlCs that can be tuned by changing spatial parameters, such as the period and height of diffraction gratings and thicknesses of functional layers. This work compares the magnetic properties of MPlCs based on Ni80Fe20 (permalloy) obtained from local (longitudinal magneto-optical Kerr effect) and bulk (vibrating-sample magnetometry) measurements and demonstrates an ability to control sensors' performance through changing the magnetic properties of the MPlCs. The influence of the substrate's geometry (planar or sinusoidal and trapezoidal diffraction grating profiles) and the thickness of the surface layer is examined.
The safety of using Gd in MRI contrast agents has recently been questioned, due to recent evidence of the retention of Gd in individuals with healthy renal function. Bone has proven to be a storage ...site for Gd, as unusually high concentrations have been measured in femoral heads of patients undergoing hip replacement surgery, as well as in autopsy samples. All previous measurements of Gd in bone have been invasive and required the bone to be removed from the body. X-ray fluorescence (XRF) offers a non-invasive and non-destructive method for carrying out in vivo measurements of Gd in humans. An updated XRF system provides improved detection limits in a short measurement time of 30-min. A new four-detector system and higher activity Cd-109 excitation source of 5GBq results in minimum detection limits (MDLs) of 1.64–1.72μgGd/g plaster for an average overlaying tissue thickness of the tibia. These levels are well within the range of previous in vitro Gd measurements. Additional validation through comparison with ICP-MS measurements has confirmed the ability of the XRF system for detecting Gd further, proving it is a feasible system to carry out human measurements.
•Methods and experimental results for the latest generation XRF system are presented.•An improved minimum detection limit of 1.64–1.72μgGd/g plaster for a 30-min measurement is reported.•Cross validation of XRF measurements with ICP-MS results in a close agreement between Gd concentration values.•XRF system provides promising results and is ready to begin in vivo human measurements.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Gadolinium (Gd) based contrast agents have been commonly used over the past three decades to improve contrast in magnetic resonance imaging. These complexes, originally thought to be stable and clear ...from the body shortly after administration, have been shown to dissociate to a small extent and deposit in organs such as bone. A safe and non-invasive method for measuring Gd in bone is necessary for further exploring Gd retention in the body following the administration of a contrast agent. A feasibility study using a K x-ray fluorescence (K-XRF) system to measure Gd in human tibias was investigated. Bone phantoms mimicking human tibia were created with Gd concentrations ranging from 0 to 120ppm. The minimum detection limit (MDL) was calculated from 20-hour and 7-hour phantom measurements with a source activity of 0.11GBq. All MDL values were scaled to a more realistic measurement time of 30-minutes with a stronger source. Scaling arguments were based on activity ratio, measurement time, and system dead time. The MDL for a 1GBq source was estimated to be 3.60–3.64ppm, for an average range of tissue thicknesses overlaying a human tibia. For a stronger source of 5GBq and a four detector cloverleaf system, the MDL was estimated to be 1.49–1.52ppm. Determined and predicted MDLs are within the range of previous in-vitro Gd measurement data. The K-XRF system shows promising results for detecting Gd in bone and should be seriously considered for in-vivo measurements.
•The feasibility of using X-ray fluorescence to detect gadolinium in bone in vivo is explored.•Bone phantoms mimicking human tibia were doped with gadolinium concentrations ranging from 0 to 120ppm.•The current X-ray fluorescence system results in a minimum detection limit of 3.60–3.64ppm.•A stronger source and improved detector system predicts an improved minimum detection limit of 1.49–1.52ppm.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Spin-wave dynamics were studied in an extended thin film of single-crystalline yttrium iron garnet using time-resolved scanning transmission x-ray microscopy. A combination of mechanical grinding and ...focused ion beam milling has been utilized to achieve a soft x-ray transparent thickness of the underlying bulk gadolinium gallium garnet substrate. Damon-Eshbach type spin waves down to about 100 nm wavelength have been directly imaged in real space for varying frequencies and external magnetic fields. The dispersion relation extracted from the experimental data agreed well with theoretical predictions. A significant influence of the ion milling process on the local magnetic properties was not detected.
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Scanning transmission x-ray microscopy has been used to image electric currents in superconducting films at temperatures down to 20 K. We detect significant deviations from a regular current path ...driven by macroscopic geometrical constraints. The magnetic stray field of supercurrents in a thin YBaCuO film is mapped into a soft-magnetic coating of permalloy. The so-created local magnetization of the ferromagnetic film can be detected by dichroic absorption of polarized x rays. To enable high-quality measurements in transmission geometry, the whole heterostructure of ferromagnet, superconductor, and single-crystalline substrate has been thinned to an overall thickness of less than 1 µm. With this technique, local supercurrents can be analyzed in a wide range of temperatures and magnetic fields. The less than 100 nm spatial resolution of the magnetic signal together with simultaneously obtained nanostructural data allow the correlation of local supercurrents with the micro- and nanostructure of the superconducting film.
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