Johannes Wild
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Research Subjects
Johannes Wild has a total of 49 co-authors. Here are the top co-authors by number of shared publications:
- Christian Horst Back
Technical University of Munich
3 shared publications - Josef Zweck
Physics Department, University of Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany
3 shared publications - Achim Rosch
Institute for Theoretical Physics, University of Cologne, 50937 Cologne, Germany
2 shared publications - Andreas Bauer
Technical University of Munich
2 shared publications - Christian Pfleiderer
Technische Universität München
2 shared publications J. Zweck
Institut für Experimentelle Physik, Universität Regensburg, Universitätsstraße 31, D-93040 Regensburg, Germany
2 shared publications
Latest Publications
- 13 March 2023
- Published by American Physical Society (APS) in Physical Review B
- Vol. 107 (10) , L100409
Driving a magnetic texture by magnon currents
Thermally induced spin dynamics in solids have sparked broad interest in both fundamental physics and spintronic applications. As theoretically proposed, thermally excited magnons created by temperature gradients can be used to manipulate spin textures such as topological magnetic solitons. However, so far, the effectiveness of such thermomagnonic torques remained a problem in practice. Here, the dynamics of magnetic vortex cores in thin ferromagnetic platelets driven by thermomagnonic torques are investigated using high-resolution Lorentz transmission electron microscopy. Large deflections of the magnetic vortex core transverse to the direction of the temperature gradient are observed. A generalized Thiele equation model is used to identify the magnitude of the contribution of the involved torques. Our results pave the way for the manipulation of magnetic domains on the nanoscale by thermomagnonic currents and provide insights into the interplay of temperature and spin.
- 13 March 2023
- Published by American Physical Society (APS) in Physical Review B
- Vol. 107 (10) , L100409
Driving a magnetic texture by magnon currents
Thermally induced spin dynamics in solids have sparked broad interest in both fundamental physics and spintronic applications. As theoretically proposed, thermally excited magnons created by temperature gradients can be used to manipulate spin textures such as topological magnetic solitons. However, so far, the effectiveness of such thermomagnonic torques remained a problem in practice. Here, the dynamics of magnetic vortex cores in thin ferromagnetic platelets driven by thermomagnonic torques are investigated using high-resolution Lorentz transmission electron microscopy. Large deflections of the magnetic vortex core transverse to the direction of the temperature gradient are observed. A generalized Thiele equation model is used to identify the magnitude of the contribution of the involved torques. Our results pave the way for the manipulation of magnetic domains on the nanoscale by thermomagnonic currents and provide insights into the interplay of temperature and spin.
- Open Access
- 1 September 2017
- Published by American Association for the Advancement of Science (AAAS) in Science Advances
- Vol. 3 (9) , e1701704-1701704
Entropy-limited topological protection of skyrmions
Magnetic skyrmions are topologically protected whirls that decay through singular magnetic configurations known as Bloch points. We used Lorentz transmission electron microscopy to infer the energetics associated with the topological decay of magnetic skyrmions far from equilibrium in the chiral magnet Fe1−xCoxSi. We observed that the lifetime τ of the skyrmions depends exponentially on temperature, . The prefactor τ0 of this Arrhenius law changes by more than 30 orders of magnitude for small changes of the magnetic field, reflecting a substantial reduction of the lifetime of skyrmions by entropic effects and, thus, an extreme case of enthalpy-entropy compensation. Such compensation effects, being well known across many different scientific disciplines, affect topological transitions and, thus, topological protection on an unprecedented level.- 1 September 2017
- Published by American Association for the Advancement of Science (AAAS) in Science Advances
- Vol. 3 (9) , e1701704-1701704
Open AccessEntropy-limited topological protection of skyrmions
Magnetic skyrmions are topologically protected whirls that decay through singular magnetic configurations known as Bloch points. We used Lorentz transmission electron microscopy to infer the energetics associated with the topological decay of magnetic skyrmions far from equilibrium in the chiral magnet Fe1−xCoxSi. We observed that the lifetime τ of the skyrmions depends exponentially on temperature, . The prefactor τ0 of this Arrhenius law changes by more than 30 orders of magnitude for small changes of the magnetic field, reflecting a substantial reduction of the lifetime of skyrmions by entropic effects and, thus, an extreme case of enthalpy-entropy compensation. Such compensation effects, being well known across many different scientific disciplines, affect topological transitions and, thus, topological protection on an unprecedented level. - 19 May 2017
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 118 (20) , 207205
Dynamical Defects in Rotating Magnetic Skyrmion Lattices
The chiral magnet hosts a Skyrmion lattice that may be equivalently described as a superposition of plane waves or a lattice of particlelike topological objects. A thermal gradient may break up the Skyrmion lattice and induce rotating domains, raising the question of which of these scenarios better describes the violent dynamics at the domain boundaries. Here, we show that in an inhomogeneous temperature gradient caused by illumination in a Lorentz transmission electron microscope different parts of the Skyrmion lattice can be set into motion with different angular velocities. Tracking the time dependence, we show that the constant rearrangement of domain walls is governed by dynamic 5–7 defects arranging into lines. An analysis of the associated defect density is described by Frank’s equation and agrees well with classical 2D Monte Carlo simulations. Fluctuations of boundaries show a surgelike rearrangement of Skyrmion clusters driven by defect rearrangement consistent with simulations treating Skyrmions as point particles. Our findings underline the particle character of the Skyrmion.- 19 May 2017
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 118 (20) , 207205
Dynamical Defects in Rotating Magnetic Skyrmion Lattices
The chiral magnet hosts a Skyrmion lattice that may be equivalently described as a superposition of plane waves or a lattice of particlelike topological objects. A thermal gradient may break up the Skyrmion lattice and induce rotating domains, raising the question of which of these scenarios better describes the violent dynamics at the domain boundaries. Here, we show that in an inhomogeneous temperature gradient caused by illumination in a Lorentz transmission electron microscope different parts of the Skyrmion lattice can be set into motion with different angular velocities. Tracking the time dependence, we show that the constant rearrangement of domain walls is governed by dynamic 5–7 defects arranging into lines. An analysis of the associated defect density is described by Frank’s equation and agrees well with classical 2D Monte Carlo simulations. Fluctuations of boundaries show a surgelike rearrangement of Skyrmion clusters driven by defect rearrangement consistent with simulations treating Skyrmions as point particles. Our findings underline the particle character of the Skyrmion.- 1 September 2016
- Published by Elsevier in Ultramicroscopy
- Vol. 168, 53-64
On detector linearity and precision of beam shift detection for quantitative differential phase contrast applications
- 1 September 2016
- Published by Elsevier in Ultramicroscopy
- Vol. 168, 53-64
On detector linearity and precision of beam shift detection for quantitative differential phase contrast applications
- 7 March 2016
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 119 (9) , 095713
Determination of polarization fields in group III-nitride heterostructures by capacitance-voltage-measurements
The polarization fields in wurtzite group III-nitrides strongly influence the optical properties of InAlGaN-based light emitters, e.g., the electron and hole wave function overlap in quantum wells. In this paper, we propose a new approach to determine these fields by capacitance-voltage measurements (CVM). Sheet charges generated by a change of the microscopic polarization at heterointerfaces influence the charge distribution in PIN junctions and therefore the depletion width and the capacitance. We show that it is possible to determine the strength and direction of the internal fields by comparing the depletion widths of two PIN junctions, one influenced by internal polarization fields and one without as a reference. For comparison, we conducted coupled Poisson/carrier transport simulations on the CVM of the polarization-influenced sample. We also demonstrate the feasibility and limits of the method by determining the fields in GaN/InGaN and GaN/AlGaN double heterostructures on (0001) c-plane grown by metal organic vapor phase epitaxy and compare both evaluation methods. The method yields (−0.50 ± 0.07) MV/cm for In0.08Ga0.92N/GaN, (0.90 ± 0.13) MV/cm for Al0.18Ga0.82N/GaN, and (2.0 ± 0.3) MV/cm for Al0.31Ga0.69N/GaN heterostructures.
- 7 March 2016
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 119 (9) , 095713
Determination of polarization fields in group III-nitride heterostructures by capacitance-voltage-measurements
The polarization fields in wurtzite group III-nitrides strongly influence the optical properties of InAlGaN-based light emitters, e.g., the electron and hole wave function overlap in quantum wells. In this paper, we propose a new approach to determine these fields by capacitance-voltage measurements (CVM). Sheet charges generated by a change of the microscopic polarization at heterointerfaces influence the charge distribution in PIN junctions and therefore the depletion width and the capacitance. We show that it is possible to determine the strength and direction of the internal fields by comparing the depletion widths of two PIN junctions, one influenced by internal polarization fields and one without as a reference. For comparison, we conducted coupled Poisson/carrier transport simulations on the CVM of the polarization-influenced sample. We also demonstrate the feasibility and limits of the method by determining the fields in GaN/InGaN and GaN/AlGaN double heterostructures on (0001) c-plane grown by metal organic vapor phase epitaxy and compare both evaluation methods. The method yields (−0.50 ± 0.07) MV/cm for In0.08Ga0.92N/GaN, (0.90 ± 0.13) MV/cm for Al0.18Ga0.82N/GaN, and (2.0 ± 0.3) MV/cm for Al0.31Ga0.69N/GaN heterostructures.
- 4 December 2015
- Published by Wiley in Physica Status Solidi (b)
- Vol. 253 (1) , 67-72
Defect reduced selectively grown GaN pyramids as template for green InGaN quantum wells
Authoren We report the growth of green emitting InGaN quantum wells (QWs) by metal‐organic vapor‐phase epitaxy (MOVPE) on three‐dimensional GaN templates. The facets of GaN pyramids, fabricated by selective‐area growth (SAG), reduce the influence of the quantum‐confined Stark effect (QCSE) on the emission properties of the QW. The luminescence properties of a QW are a good indicator for the crystalline quality of the GaN layer beneath. Especially the presence of voids inside the pyramids, as well as stacking faults (SFs) and threading dislocations (TDs) in the wing region strongly influence the strain situation and the incorporation of In into the overlying InGaN layer. Thus, the crystal quality of the GaN pyramid has a strong influence on the efficiency and the emission properties of the active region. Therefore, a low‐temperature nucleation on the GaN buffer in conjunction with a decreasing Ga‐flux taking the decreasing c‐plane growth surface of the pyramid into account was introduced. The low‐temperature photoluminescence (PL) properties of the InGaN QW reveal the differences between the standard formation of the pyramid and this modified growth. Cathodoluminescence (CL) and transmission electron microscopy (TEM) measurements confirm the differences between the two growth modes in the crystal quality of the inner part of the pyramid.
- 4 December 2015
- Published by Wiley in Physica Status Solidi (b)
- Vol. 253 (1) , 67-72
Defect reduced selectively grown GaN pyramids as template for green InGaN quantum wells
Authoren We report the growth of green emitting InGaN quantum wells (QWs) by metal‐organic vapor‐phase epitaxy (MOVPE) on three‐dimensional GaN templates. The facets of GaN pyramids, fabricated by selective‐area growth (SAG), reduce the influence of the quantum‐confined Stark effect (QCSE) on the emission properties of the QW. The luminescence properties of a QW are a good indicator for the crystalline quality of the GaN layer beneath. Especially the presence of voids inside the pyramids, as well as stacking faults (SFs) and threading dislocations (TDs) in the wing region strongly influence the strain situation and the incorporation of In into the overlying InGaN layer. Thus, the crystal quality of the GaN pyramid has a strong influence on the efficiency and the emission properties of the active region. Therefore, a low‐temperature nucleation on the GaN buffer in conjunction with a decreasing Ga‐flux taking the decreasing c‐plane growth surface of the pyramid into account was introduced. The low‐temperature photoluminescence (PL) properties of the InGaN QW reveal the differences between the standard formation of the pyramid and this modified growth. Cathodoluminescence (CL) and transmission electron microscopy (TEM) measurements confirm the differences between the two growth modes in the crystal quality of the inner part of the pyramid.