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- ItemInter-granular effects at high magnetic fields of cuprate and iron chalcogenide superconducting materials(Bristol : Institute of Physics Publishing, 2019) Buchkov, K.; Valkovski, M.; Gajda, D.; Nenkov, K.; Nazarova, E.The weak links effects are one of the main challenges for effective power applications of high temperature superconducting materials. Studies of these effects help for their better understanding and subsequent improvement. An overview analysis of the intergranular properties of cuprate (Y0.8Ca0.2Ba2Cu3O7-δ) and iron-based chalcogenide (FeSe0.5Te0.5) polycrystalline samples was carried out, by means of series of electro-transport experiments at different magnetic fields. The temperature evolution of the Josephson coupling and intrinsic superconductivity effects for the both systems was constructed. The FeSe0.5Te0.5 compound shows very stable and superior behavior compared to Y0.8Ca0.2BCO up to the highest magnetic fields (14T) used. We have explored FeSe0.5Te0.5 Josephson weak links influence (as a non-linear process) over the resistive transition using different AC current amplitudes and applying the sensitive AC transport third harmonics technique.
- ItemThe missing links of neutron star evolution in the eROSITA all-sky X-ray survey(Bristol : IOP Publ., 2017) Pires, A.M.The observational manifestation of a neutron star is strongly connected with the properties of its magnetic field. During the star's lifetime, the field strength and its changes dominate the thermo-rotational evolution and the source phenomenology across the electromagnetic spectrum. Signatures of magnetic field evolution are best traced among elusive groups of X-ray emitting isolated neutron stars (INSs), which are mostly quiet in the radio and γ-ray wavelengths. It is thus important to investigate and survey INSs in X-rays in the hope of discovering peculiar sources and the long-sought missing links that will help us to advance our understanding of neutron star evolution. The Extended Röntgen Survey with an Imaging Telescope Array (eROSITA), the primary instrument on the forthcoming Spectrum-RG mission, will scan the X-ray sky with unprecedented sensitivity and resolution. The survey has thus the unique potential to unveil the X-ray faint end of the neutron star population and probe sources that cannot be assessed by standard pulsar surveys.
- ItemStructural properties of magnetic nanoparticles determine their heating behavior - an estimation of the in vivo heating potential(New York, NY [u.a.] : Springer, 2014) Ludwig, R.; Stapf, M.; Dutz, S.; Müller, R.; Teichgräber, U.; Hilger, I.Magnetically induced heating of magnetic nanoparticles (MNP) in an alternating magnetic field (AMF) is a promising minimally invasive tool for localized tumor treatment by sensitizing or killing tumor cells with the help of thermal stress. Therefore, the selection of MNP exhibiting a sufficient heating capacity (specific absorption rate, SAR) to achieve satisfactory temperatures in vivo is necessary. Up to now, the SAR of MNP is mainly determined using ferrofluidic suspensions and may distinctly differ from the SAR in vivo due to immobilization of MNP in tissues and cells. The aim of our investigations was to study the correlation between the SAR and the degree of MNP immobilization in dependence of their physicochemical features.In this study, the included MNP exhibited varying physicochemical properties and were either made up of single cores or multicores. Whereas the single core MNP exhibited a core size of approximately 15 nm, the multicore MNP consisted of multiple smaller single cores (5 to 15 nm) with 65 to 175 nm diameter in total. Furthermore, different MNP coatings, including dimercaptosuccinic acid (DMSA), polyacrylic acid (PAA), polyethylenglycol (PEG), and starch, wereinvestigated. SAR values were determined after the suspension of MNP in water. MNP immobilization in tissues was simulated with 1% agarose gels and 10% polyvinyl alcohol (PVA) hydrogels.The highest SAR values were observed in ferrofluidic suspensions, whereas a strong reduction of the SAR after the immobilization of MNP with PVA was found. Generally, PVA embedment led to a higher immobilization of MNP compared to immobilization in agarose gels. The investigated single core MNP exhibited higher SAR values than the multicore MNP of the same core size within the used magnetic field parameters. Multicore MNP manufactured via different synthesis routes (fluidMAG-D, fluidMAG/12-D) showed different SAR although they exhibited comparable core and hydrodynamic sizes. Additionally, no correlation between ζ-potential and SAR values after immobilization was observed.Our data show that immobilization of MNP, independent of their physicochemical properties, can distinctly affect their SAR. Similar processes are supposed to take place in vivo, particularly when MNP are immobilized in cells and tissues. This aspect should be adequately considered when determining the SAR of MNP for magnetic hyperthermia.
- ItemPinning and trapped field in MgB2- and MT-YBaCuO bulk superconductors manufactured under pressure(Bristol : IOP Publ., 2016) Prikhna, T.; Eisterer, M.; Chaud, X.; Weber, H.W.; Habisreuther, T.; Moshchil, V.; Kozyrev, A.; Shapovalov, A.; Gawalek, W.; Wu, M.; Litzkendorf, D.; Goldacker, W.; Sokolovsky, V.; Shaternik, V.; Rabier, J.; Joulain, A.; Grechnev, G.; Boutko, V.; Gusev, A.; Shaternik, A.; Barvitskiy, P.The relevant pinning centers of Abrikosov vortices in MgB2-based materials are oxygen-enriched Mg-B-O inclusions or nanolayers and inclusions of MgBx (x>4) phases. The high critical current densities, jc, of 106 and 103A/cm2 at 1 and 8.5 T, respectively, at 20 K can be achieved in polycrystalline materials (prepared at 2 GPa) containing a large amount of admixed oxygen. Besides, oxygen can be incorporated into the MgB2 structure in small amounts (MgB1.5O0.5), which is supported by Auger studies and calculations of the DOS and the binding energy. The jc of melt textured YBa2Cu3O7-δ (or Y123)-based superconductors (MT-YBaCuO) depends not only on the perfectness of texture and the amount of oxygen in the Y123 structure, but also on the density of twins and micro-cracks formed during the oxygenation (due to shrinking of the c-lattice parameter). The density of twins and microcracks increases with the reduction of the distance between Y2BaCuO5 (Y211) inclusions in Y123. At 77 K jc=8·104 A/cm2 in self-field and jc=103 A/cm2 at 10 T were found in materials oxygenated at 16 MPa for 3 days with a density of twins of 22–35 per µm (thickness of the lamellae: 45-30 nm) and a density of micro-cracks of 200–280 per mm. Pinning can occur at the points of intersection between the Y123 twin planes and the Y211 inclusions. MTYBaCuO at 77 K can trap 1.4 T (38×38×17 mm, oxygenated at 0.1 MPa for 20 days) and 0.8 T (16 mm in diameter and 10 mm thick with 0.45 mm holes oxygenated at 10 MPa for 53 h). The sensitivity of MgB2 to magnetic field variations (flux jumps) complicates estimates of the trapped field. At 20 K 1.8 T was found for a block of 30 mm in diameter and a thickness of 7.5 mm and 1.5 T (if the magnetic field was increased at a rate of 0.1 T) for a ring with dimensions 24×18 mm and a thickness of 8 mm.
- ItemShapeable magnetoelectronics(Melville, NY : American Inst. of Physics, 2016) Makarov, Denys; Melzer, Michael; Karnaushenko, Daniil; Schmidt, Oliver G.Inorganic nanomembranes are shapeable (flexible, printable, and even stretchable) and transferrable to virtually any substrate. These properties build the core concept for new technologies, which transform otherwise rigid high-speed devices into their shapeable counterparts. This research is motivated by the eagerness of consumer electronics towards being thin, lightweight, flexible, and even wearable. The realization of this concept requires all building blocks as we know them from rigid electronics (e.g., active elements, optoelectronics, magnetoelectronics, and energy storage) to be replicated in the form of (multi)functional nanomembranes, which can be reshaped on demand after fabrication. There are already a variety of shapeable devices commercially available, i.e., electronic displays, energy storage elements, and integrated circuitry, to name a few. From the beginning, the main focus was on the fabrication of shapeable high-speed electronics and optoelectronics. Only very recently, a new member featuring magnetic functionalities was added to the family of shapeable electronics. With their unique mechanical properties, the shapeable magnetic field sensor elements readily conform to ubiquitous objects of arbitrary shapes including the human skin. This feature leads electronic skin systems beyond imitating the characteristics of its natural archetype and extends their cognition to static and dynamic magnetic fields that by no means can be perceived by human beings naturally. Various application fields of shapeable magnetoelectronics are proposed. The developed sensor platform can equip soft electronic systems with navigation, orientation, motion tracking, and touchless control capabilities. A variety of novel technologies, such as smart textiles, soft robotics and actuators, active medical implants, and soft consumer electronics, will benefit from these new magnetic functionalities. This review reflects the establishment of shapeable magnetic sensorics, describing the entire development from the first attempts to verify the functional concept to the realization of ready-to-use highly compliant and strain invariant sensor devices with remarkable robustness.