2014, Hennes, M., Lotnyk, A., Mayr, S.G.

Magnetically anisotropic as well as magnetic core-shell nanoparticles (CS-NPs) with controllable properties are highly desirable in a broad range of applications. With this background, a setup for the synthesis of heterostructured magnetic core-shell nanoparticles, which relies on (optionally pulsed) DC plasma gas condensation has been developed. We demonstrate the synthesis of elemental nickel nanoparticles with highly tunable sizes and shapes and Ni@Cu CS-NPs with an average shell thickness of 10 nm as determined with scanning electron microscopy, high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy measurements. An analytical model that relies on classical kinetic gas theory is used to describe the deposition of Cu shell atoms on top of existing Ni cores. Its predictive power and possible implications for the growth of heterostructured NP in gas condensation processes are discussed.

2014, Oka, T., Yamada, Y., Horiuchi, T., Ogawa, J., Fukui, S., Sato, T., Yokoyama, K., Langer, M.

The magnetic flux penetration into the melt-textured Y-Ba-Cu-O high temperature superconducting bulk magnets were precisely evaluated during and after the pulsed field magnetization processes operated at 30 K. The bulk magnets were carefully fabricated by the cold seeding method with use of a single and a pair of seed crystals composed of the Nd-Ba-Cu-O thin films. These seed crystals were put on the top surfaces of the precursors to let the large grains grow during the heat treatments. We observed the flux penetrations which occurred in the lower applied-field regions at around 3.1 T for the samples bearing the twin seeds than those of the single-seeded crystals at around 3.8 T. This means that the magnetic fluxes are capable of invading into the twin-seeded samples more easily than the single-seeds. It suggests that the anisotropic grain growths of parallel and normal to the rows of seed crystals affects the variations of Jc values with different distributions of the pinning centers, results in the preferential paths for the invading magnetic fluxes.

2019, Kuttner, Christian, Höller, Roland P. M., Quintanilla, Marta, Schnepf, Max J., Dulle, Martin, Fery, Andreas, Liz-Marzán, Luis M.

The optical properties of nanoparticle assemblies can be tailored via hybridization of plasmon modes. Isotropic core/satellite superstructures made of spherical nanoparticles are known to exhibit coupled modes with a strongly scattering (radiative) character, and provide hot spots yielding high activity in surface-enhanced Raman scattering (SERS). However, to complement this functionality with plasmonic heating, additional absorbing (non-radiative) modes are required. We introduce herein anisotropic superstructures formed by decorating a central nanorod with spherical satellite nanoparticles, which feature two coupled modes that allow application for both SERS and heating. On the basis of diffuse reflectance spectroscopy, small-angle X-ray scattering (SAXS), and electromagnetic simulations, the origin of the coupled modes is disclosed and thus serves as a basis toward alternative designs of functional superstructures. This work represents a proof-of-principle for the combination of high SERS efficiency with efficient plasmonic heating by near-infrared irradiation.

2008, Thomas, M., Heczko, O., Buschbeck, J., Rößler, U.K., McCord, J., Scheerbaum, N., Schultz, L., Fähler, S.

Magnetically induced reorientation (MIR) is observed in epitaxial orthorhombic Ni-Mn-Ga films. Ni-Mn-Ga films have been grown epitaxially on heated MgO(001) substrates in the cubic austenite state. The unit cell is rotated by 45° relative to the MgO cell. The growth, structure texture and anisotropic magnetic properties of these films are described. The crystallographic analysis of the martensitic transition reveals variant selection dominated by the substrate constraint. The austenite state has low magnetocrystalline anisotropy. In the martensitic state, the magnetization curves reveal an orthorhombic symmetry having three magnetically non-equivalent axes. The existence of MIR is deduced from the typical hysteresis within the first quadrant in magnetization curves and independently by texture measurement without and in the presence of a magnetic field probing micro structural changes. An analytical model is presented, which describes MIR in films with constrained overall extension by the additional degree of freedom of an orthorhombic structure compared to the tetragonal structure used in the standard model.

2015, Zhang, Y., Krylov, D., Rosenkranz, M., Schiemenz, S., Popov, A. A.

Paramagnetic and variable temperature 13C and 45Sc nuclear magnetic resonance studies are performed for nitride clusterfullerenes MSc2N@C80 with icosahedral Ih(7) carbon cage, where M runs through all lanthanides forming nitride clusters. The influence of the endohedral lanthanide ions on the NMR spectral pattern is carefully followed, and dramatic differences are found in peak positions and line widths. Thus, 13C lines broaden from 0.01–0.02 ppm in diamagnetic MSc2N@C80 molecules (M = La, Y, Lu) to several ppm in TbSc2N@C80 and DySc2N@C80. Direction of the paramagnetic shift depends on the shape of the 4f electron density in corresponding lanthanide ions. In TmSc2N@C80 and ErSc2N@C80 with prolate 4f-density of lanthanide ions, 13C signals are shifted down-field, whereas 45Sc peaks are shifted up-field versus diamagnetic values. In all other MSc2N@C80 molecules lanthanide ions have oblate-shaped 4f electron density, and the lanthanide-induced shift is negative for 13C and positive for 45Sc peaks. Analysis of the pseudocontact and contact contributions to chemical shifts revealed that the pseudocontact term dominates both in 13C and 45Sc NMR spectra, although contact shifts for 13C signals are also considerable. Point charge computations of the ligand field splitting are performed to explain experimental results, and showed reasonable agreement with experimental pseudocontact shifts. Nitrogen atom bearing large negative charge and located close to the lanthanide ion results in large magnetic anisotropy of lanthanide ions in nitride clusterfullerenes with quasi-uniaxial ligand field.

2020, Schindler, Clemens, Gorbunov, Denis, Zherlitsyn, Sergei, Galeski, Stanislaw, Schmidt, Marcus, Wosnitza, Jochen, Gooth, Johannes

In this study, we report on the observation of de Haas-van Alphen-type quantum oscillations (QOs) in the ultrasound velocity of NbP as well as "giant QOs"in the ultrasound attenuation in pulsed magnetic fields. The difference in the QO amplitude for different acoustic modes reveals a strong anisotropy of the effective deformation potential, which we estimate to be as high as 9eV for certain parts of the Fermi surface. Furthermore, the natural filtering of QO frequencies and the tracing of the individual Landau levels to the quantum limit allows for a more detailed investigation of the Fermi surface of NbP, as was previously achieved by means of analyzing QOs observed in magnetization or electrical resistivity. © 2020 authors. Published by the American Physical Society.

2018, Rose, Jonas C., Gehlen, David B., Haraszti, Tamás, Köhler, Jens, Licht, Christopher J., De Laporte, Laura

Natural healing is based on highly orchestrated processes, in which the extracellular matrix plays a key role. To resemble the native cell environment, we introduce an artificial extracellular matrix (aECM) with the capability to template hierarchical and anisotropic structures in situ, allowing a minimally-invasive application via injection. Synthetic, magnetically responsive, rod-shaped microgels are locally aligned and fixed by a biocompatible surrounding hydrogel, creating a hybrid anisotropic hydrogel (Anisogel), of which the physical, mechanical, and chemical properties can be tailored. The microgels are rendered cell-adhesive with GRGDS and incorporated either inside a cell-adhesive fibrin or bioinert poly(ethylene glycol) hydrogel to strongly interact with fibroblasts. GRGDS-modified microgels inside a fibrin-based Anisogel enhance fibroblast alignment and lead to a reduction in fibronectin production, indicating successful replacement of structural proteins. In addition, YAP-translocation to the nucleus increases with the concentration of microgels, indicating cellular sensing of the overall anisotropic mechanical properties of the Anisogel. For bioinert surrounding PEG hydrogels, GRGDS-microgels are required to support cell proliferation and fibronectin production. In contrast to fibroblasts, primary nerve growth is not significantly affected by the biomodification of the microgels. In conclusion, this approach opens new opportunities towards advanced and complex aECMs for tissue regeneration.

2012, Calvimontes, A., Mauermann, M., Bellmann, C.

Microscopic and physico-chemical methods were used for a comprehensive surface characterization of different mechanically modified stainless steel surfaces. The surfaces were analyzed using high-resolution confocal microscopy, resulting in detailed information about the topographic properties. In addition, static water contact angle measurements were carried out to characterize the surface heterogeneity of the samples. The effect of morphological anisotropy on water contact angle anisotropy was investigated. The correlation between topography and wetting was studied by means of a model of wetting proposed in the present work, that allows quantifying the air volume of the interface water drop-stainless steel surface.

2020, Rose, Jonas C., Fölster, Maaike, Kivilip, Lukas, Gerardo-Nava, Jose L., Jaekel, Esther E., Gehlen, David B., Rohlfs, Wilko, De Laporte, Laura

Living multicellular organisms comprise a high degree of soft anisotropic tissues but the development of controlled artificial assembly processes to mimic them remains challenging. Therefore, injectable, polymeric, magneto-responsive microgel rods are fabricated to orient within a low magnetic field. The incorporated superparamagnetic nanoparticles induce local dipole moments, resulting in a total magnetic torque that endows microgels with different structural, mechanical, and biochemical properties. In this report, a predictive macroscopic model based on an ellipsoidal element dispersed in a Newtonian fluid is adjusted using experimental data, which enables the prediction of the orientation rate and the required magnetic field strength for various microgel design parameters and fluid viscosities. The ordered microgels are fixed by crosslinking of a surrounding hydrogel, and can be employed for a wide variety of applications where anisotropic composite hydrogels play a crucial role; for instance as adaptive materials or in biomedical applications, wherein the model predictions can reduce animal experiments. © 2019 The Royal Society of Chemistry.

2019, Simmendinger, J., Hanisch, J., Bihler, M., Ionescu, A.M., Weigand, M., Sieger, M., Hühne, R., Rijckaert, H., Van Driessche, I., Schütz, G., Albrecht, J.

We studied the impact of soft ferromagnetic permalloy (Py) on the shielding currents in a strong-pinning superconductor - YBa2Cu3O7-δ with Ba2Y(Nb/Ta)O6 nano-precipitates - by means of scanning transmission x-ray microscopy. Typically and in particular when in the thin film limit, superconductor/ferromagnet (SC/FM) bilayers exhibit isotropic properties of the flux line ensemble at all temperatures. However, in elements with small aspect ratio a significant anisotropy in flux penetration is observed. We explain this effect by local in-plane fields arising from anisotropic magnetic stray fields originated by the ferromagnet. This leads to direction-dependent motion of magnetic vortices inside the SC/FM bilayer. Our results demonstrate that small variations of the magnetic properties can have huge impact on the superconductor.