9 results
Search Results
Now showing 1 - 9 of 9
- ItemPlasma-assisted synthesis and high-resolution characterization of anisotropic elemental and bimetallic core-shell magnetic nanoparticles(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 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.
- ItemMagnetic flux-trapping of anisotropic-grown Y-Ba-Cu-O bulk superconductors during and after pulsed-field magnetizing processes(Milton Park : Taylor & Francis, 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.
- ItemStrong anisotropy of the electron-phonon interaction in NbP probed by magnetoacoustic quantum oscillations(Woodbury, NY : Inst., 2020) Schindler, Clemens; Gorbunov, Denis; Zherlitsyn, Sergei; Galeski, Stanislaw; Schmidt, Marcus; Wosnitza, Jochen; Gooth, JohannesIn 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.
- ItemMagnetically induced anisotropy of flux penetration into strong-pinning superconductor/ferromagnet bilayers(Bristol : Institute of Physics Publishing, 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.
- ItemMagnetically induced reorientation of martensite variants in constrained epitaxial Ni-Mn-Ga films grown on MgO(001)(Milton Park : Taylor & Francis, 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.
- ItemTunable chirality of noncentrosymmetric magnetic Weyl semimetals in rare-earth carbides([London] : Nature Publishing Group, 2022) Ray, Rajyavardhan; Sadhukhan, Banasree; Richter, Manuel; Facio, Jorge I.; van den Brink, JeroenEven if Weyl semimetals are characterized by quasiparticles with well-defined chirality, exploiting this experimentally is severely hampered by Weyl lattice fermions coming in pairs with opposite chirality, typically causing the net chirality picked up by experimental probes to vanish. Here, we show this issue can be circumvented in a controlled manner when both time-reversal- and inversion symmetry are broken. To this end, we investigate chirality disbalance in the carbide family RMC2 (R a rare-earth and M a transition metal), showing several members to be Weyl semimetals. Using the noncentrosymmetric ferromagnet NdRhC2 as an illustrating example, we show that an odd number of Weyl nodes can be stabilized at its Fermi surface by properly tilting its magnetization. The chiral configuration endows a topological phase transition as the Weyl node transitions across the Fermi sheets, which triggers interesting chiral electromagnetic responses. Further, the tilt direction determines the sign of the resulting net chirality, opening up a simple route to control its sign and strength.
- ItemCoupling of chiralities in spin and physical spaces: The Möbius ring as a case study(College Park : American Physical Society, 2015) Pylypovskyi, Oleksandr V.; Kravchuk, Volodymyr P.; Sheka, Denis D.; Makarov, Denys; Schmidt, Oliver G.; Gaididei, YuriWe show that the interaction of the magnetic subsystem of a curved magnet with the magnet curvature results in the coupling of a topologically nontrivial magnetization pattern and topology of the object. The mechanism of this coupling is explored and illustrated by an example of a ferromagnetic Möbius ring, where a topologically induced domain wall appears as a ground state in the case of strong easy-normal anisotropy. For the Möbius geometry, the curvilinear form of the exchange interaction produces an additional effective Dzyaloshinskii-like term which leads to the coupling of the magnetochirality of the domain wall and chirality of the Möbius ring. Two types of domain walls are found, transversal and longitudinal, which are oriented across and along the Möbius ring, respectively. In both cases, the effect of magnetochirality symmetry breaking is established. The dependence of the ground state of the Möbius ring on its geometrical parameters and on the value of the easy-normal anisotropy is explored numerically.
- ItemMueller matrix imaging microscope using dual continuously rotating anisotropic mirrors(Washington, DC : Soc., 2021) Ruder, Alexander; Wright, Brandon; Feder, Rene; Kilic, Ufuk; Hilfiker, Matthew; Schubert, Eva; Herzinger, Craig M.; Schubert, MathiasWe demonstrate calibration and operation of a Mueller matrix imaging microscope using dual continuously rotating anisotropic mirrors for polarization state generation and analysis. The mirrors contain highly spatially coherent nanostructure slanted columnar titanium thin films deposited onto optically thick titanium layers on quartz substrates. The first mirror acts as polarization state image generator and the second mirror acts as polarization state image detector. The instrument is calibrated using samples consisting of laterally homogeneous properties such as straight-through-air, a clear aperture linear polarizer, and a clear aperture linear retarder waveplate. Mueller matrix images are determined for spatially varying anisotropic samples consisting of a commercially available (Thorlabs) birefringent resolution target and a spatially patterned titanium slanted columnar thin film deposited onto a glass substrate. Calibration and operation are demonstrated at a single wavelength (530 nm) only, while, in principle, the instrument can operate regardless of wavelength. We refer to this imaging ellipsometry configuration as rotating-anisotropic-mirror-sample-rotating-anisotropic-mirror ellipsometry (RAM-S-RAM-E).
- ItemAnisotropic fractal magnetic domain pattern in bulk Mn1.4PtSn(Woodbury, NY : Inst., 2020) Sukhanov, A.S.; Zuniga Cespedes, B.E.; Vir, P.; Cameron, A.S.; Heinemann, A.; Martin, N.; Chaboussant, G.; Kumar, V.; Milde, P.; Eng, L.M.; Felser, C.; Inosov, D.S.The tetragonal compound Mn1.4PtSn with D2d symmetry recently attracted attention as the first known material that hosts magnetic antiskyrmions, which differ from the skyrmions known so far by their internal structure. The latter have been found in a number of magnets with the chiral crystal structure. In previous works, the existence of antiskyrmions in Mn1.4PtSn was unambiguously demonstrated in real space by means of Lorentz transmission electron microscopy on thin-plate samples (∼100 nm thick). In the present study, we used small-angle neutron scattering and magnetic force microscopy to perform reciprocal- and real-space imaging of the magnetic texture of bulk Mn1.4PtSn single crystals at different temperatures and in applied magnetic field. We found that the magnetic texture in the bulk differs significantly from that of thin-plate samples. Instead of spin helices or an antiskyrmion lattice, we observe an anisotropic fractal magnetic pattern of closure domains in zero field above the spin-reorientation transition temperature, which transforms into a set of bubble domains in high field. Below the spin-reorientation transition temperature the strong in-plane anisotropy as well as the fractal self-affinity in zero field is gradually lost, while the formation of bubble domains in high field remains robust. The results of our study highlight the importance of dipole-dipole interactions in thin-plate samples for the stabilization of antiskyrmions and identify criteria which should guide the search for potential (anti)skyrmion host materials. Moreover, they provide consistent interpretations of the previously reported magnetotransport anomalies of the bulk crystals. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.