Kern, L. -M.; Kuchkin, V. M.; Deinhart, V.; Klose, C.; Sidiropoulos, T.; Auer, M.; Gaebel, S.; Gerlinger, K.; Battistelli, R.; Wittrock, S.; Karaman, T.; Schneider, M.; Günther, C. M.; Engel, D.; Will, I.; Wintz, S.; Weigand, M.; Büttner, F.; Höflich, K.; Eisebitt, S.; Pfau, B. Controlled Formation of Skyrmion Bags Journal Article Adv. Mater. 2501250 (2025), (contributed). @article{kern_controlled_2025,
title = {Controlled Formation of Skyrmion Bags},
author = {L. -M. Kern and V. M. Kuchkin and V. Deinhart and C. Klose and T. Sidiropoulos and M. Auer and S. Gaebel and K. Gerlinger and R. Battistelli and S. Wittrock and T. Karaman and M. Schneider and C. M. Günther and D. Engel and I. Will and S. Wintz and M. Weigand and F. Büttner and K. Höflich and S. Eisebitt and B. Pfau},
url = {https://advanced.onlinelibrary.wiley.com/doi/abs/10.1002/adma.202501250},
doi = {10.1002/adma.202501250},
year = {2025},
date = {2025-04-28},
urldate = {2025-04-01},
journal = {Adv. Mater.},
pages = {2501250},
abstract = {Abstract Topologically non-trivial magnetic solitons are complex spin textures with a distinct single-particle nature. Although magnetic skyrmions, especially those with unity topological charge, have attracted substantial interest due to their potential applications, more complex topological textures remain largely theoretical. In this work, the stabilization of isolated higher-order skyrmion bags beyond the prototypical π-skyrmion in ferromagnetic thin films is experimentally demonstrate, which has posed considerable challenges to date. Specifically, controlled generation of skyrmionium (2π-skyrmion), target skyrmion (3π-skyrmion), and skyrmion bags (with variable topological charge) are achieved through the introduction of artificially engineered anisotropy defects via local ion irradiation. They act as preferential sites for the field- or laser-induced nucleation of skyrmion bags. Remarkably, ultrafast laser pulses achieve a substantially higher conversion rate transforming skyrmions into higher-order skyrmion bags compared to their formation driven by magnetic fields. High-resolution x-ray imaging enables direct observation of the resulting skyrmion bags. Complementary micromagnetic simulations reveal the pivotal role of defect geometry–particularly diameter–in stabilizing closed-loop domain textures. The findings not only broaden the experimental horizon for skyrmion research, but also suggest strategies for exploiting complex topological spin textures within a unified material platform for practical applications.},
note = {(contributed)},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Topologically non-trivial magnetic solitons are complex spin textures with a distinct single-particle nature. Although magnetic skyrmions, especially those with unity topological charge, have attracted substantial interest due to their potential applications, more complex topological textures remain largely theoretical. In this work, the stabilization of isolated higher-order skyrmion bags beyond the prototypical π-skyrmion in ferromagnetic thin films is experimentally demonstrate, which has posed considerable challenges to date. Specifically, controlled generation of skyrmionium (2π-skyrmion), target skyrmion (3π-skyrmion), and skyrmion bags (with variable topological charge) are achieved through the introduction of artificially engineered anisotropy defects via local ion irradiation. They act as preferential sites for the field- or laser-induced nucleation of skyrmion bags. Remarkably, ultrafast laser pulses achieve a substantially higher conversion rate transforming skyrmions into higher-order skyrmion bags compared to their formation driven by magnetic fields. High-resolution x-ray imaging enables direct observation of the resulting skyrmion bags. Complementary micromagnetic simulations reveal the pivotal role of defect geometry–particularly diameter–in stabilizing closed-loop domain textures. The findings not only broaden the experimental horizon for skyrmion research, but also suggest strategies for exploiting complex topological spin textures within a unified material platform for practical applications. |
Metternich, D.; Litzius, K.; Wintz, S.; Gerlinger, K.; Petz, S.; Engel, D.; Sidiropoulos, T.; Battistelli, R.; Steinbach, F.; Weigand, M.; Wittrock, S.; Schmising, C. Korff; Büttner, F. Defects in magnetic domain walls after single-shot all-optical switching Journal Article Struct. Dyn. 12, 024504 (2025). @article{metternich_defects_2025,
title = {Defects in magnetic domain walls after single-shot all-optical switching},
author = {D. Metternich and K. Litzius and S. Wintz and K. Gerlinger and S. Petz and D. Engel and T. Sidiropoulos and R. Battistelli and F. Steinbach and M. Weigand and S. Wittrock and C. Korff Schmising and F. Büttner},
url = {https://doi.org/10.1063/4.0000287},
doi = {10.1063/4.0000287},
year = {2025},
date = {2025-04-18},
urldate = {2025-04-01},
journal = {Struct. Dyn.},
volume = {12},
number = {2},
pages = {024504},
abstract = {Helicity-independent all-optical switching (HI-AOS) is the fastest known way to switch the magnetic order parameter. While the switching process of extended areas is well understood, the formation of domain walls enclosing switched areas remains less explored. Here, we study domain walls around all-optically nucleated magnetic domains using x-ray vector spin imaging and observe a high density of vertical Bloch line defects. Surprisingly, the defect density appears to be independent of optical pulse parameters, significantly varies between materials, and is only slightly higher than in domain walls generated by field cycling. A possible explanation is given by time-resolved Kerr microscopy, which reveals that magnetic domains considerably expand after the initial AOS process. During this expansion, and likewise during field cycling, domain walls propagate at speeds above the Walker breakdown. Micromagnetic simulations suggest that at such speeds, domain walls accumulate defects when moving over magnetic pinning sites, explaining similar defect densities after two very different switching processes. The slightly larger defect density after AOS compared to field-induced switching indicates that some defects are created already when the domain wall comes into existence. Our work shows that engineered low-pinning materials are a key ingredient to uncover the intrinsic dynamics of domain wall formation during ultrafast all-optical switching.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Helicity-independent all-optical switching (HI-AOS) is the fastest known way to switch the magnetic order parameter. While the switching process of extended areas is well understood, the formation of domain walls enclosing switched areas remains less explored. Here, we study domain walls around all-optically nucleated magnetic domains using x-ray vector spin imaging and observe a high density of vertical Bloch line defects. Surprisingly, the defect density appears to be independent of optical pulse parameters, significantly varies between materials, and is only slightly higher than in domain walls generated by field cycling. A possible explanation is given by time-resolved Kerr microscopy, which reveals that magnetic domains considerably expand after the initial AOS process. During this expansion, and likewise during field cycling, domain walls propagate at speeds above the Walker breakdown. Micromagnetic simulations suggest that at such speeds, domain walls accumulate defects when moving over magnetic pinning sites, explaining similar defect densities after two very different switching processes. The slightly larger defect density after AOS compared to field-induced switching indicates that some defects are created already when the domain wall comes into existence. Our work shows that engineered low-pinning materials are a key ingredient to uncover the intrinsic dynamics of domain wall formation during ultrafast all-optical switching. |
Hua, N.; Breitner, F.; Jesche, A.; Huang, S. -W.; Rüegg, C.; Gegenwart, P. Structural and magnetic properties of β-Li2IrO3 after grazing-angle focused ion beam thinning Journal Article Acta Crystallogr. B 81, 202 (2025). @article{hua_structural_2025,
title = {Structural and magnetic properties of β-Li_{2}IrO_{3} after grazing-angle focused ion beam thinning},
author = {N. Hua and F. Breitner and A. Jesche and S. -W. Huang and C. Rüegg and P. Gegenwart},
url = {https://doi.org/10.1107/S2052520625000587},
doi = {10.1107/S2052520625000587},
year = {2025},
date = {2025-04-01},
urldate = {2025-04-01},
journal = {Acta Crystallogr. B},
volume = {81},
number = {2},
pages = {202},
abstract = {Manipulating the size and orientation of quantum materials is often used to tune emergent phenomena, but precise control of these parameters is also necessary from an experimental point of view. Various synthesis techniques already exist, such as epitaxial thin film growth and chemical etching, that are capable of producing specific sample dimensions with high precision. However, certain materials exist as single crystals that are often difficult to manipulate, thereby limiting their studies to a certain subset of experimental techniques. One particular class of these materials includes lithium and sodium iridates, which are promising candidates for hosting a Kitaev quantum spin liquid state. Here a controlled method of using a focused ion beam at grazing incidence to reduce the size of a β-Li_2IrO_3 single crystal to a thickness of 1–2𝜇m is presented. Subsequent X-ray diffraction measurements show the lattice remains intact, albeit with a larger mosaic spread. The integrity of the magnetic order is also preserved as the temperature dependent magnetic diffraction peak follows the same trend as its bulk counterpart with a transition temperature at textitT = 37.5K. Our study demonstrates a technique that opens up the possibility of nonequilibrium experiments where submicron thin samples are often essential.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Manipulating the size and orientation of quantum materials is often used to tune emergent phenomena, but precise control of these parameters is also necessary from an experimental point of view. Various synthesis techniques already exist, such as epitaxial thin film growth and chemical etching, that are capable of producing specific sample dimensions with high precision. However, certain materials exist as single crystals that are often difficult to manipulate, thereby limiting their studies to a certain subset of experimental techniques. One particular class of these materials includes lithium and sodium iridates, which are promising candidates for hosting a Kitaev quantum spin liquid state. Here a controlled method of using a focused ion beam at grazing incidence to reduce the size of a β-Li_2IrO_3 single crystal to a thickness of 1–2𝜇m is presented. Subsequent X-ray diffraction measurements show the lattice remains intact, albeit with a larger mosaic spread. The integrity of the magnetic order is also preserved as the temperature dependent magnetic diffraction peak follows the same trend as its bulk counterpart with a transition temperature at textitT = 37.5K. Our study demonstrates a technique that opens up the possibility of nonequilibrium experiments where submicron thin samples are often essential. |
Halloran, T.; Wang, Y.; Plumb, K. W.; Stone, M. B.; Winn, B.; Graves-Brook, M. K.; Rodriguez-Rivera, J. A.; Qui, Y.; Chauhan, P.; Knolle, J.; Moessner, R.; Armitage, N. P.; Takayama, T.; Takagi, H.; Broholm, C. Continuum of magnetic excitations in the Kitaev honeycomb iridate D3LiIr2O6 Journal Article npj Quantum Mater. 10, 35 (2025). @article{halloran_continuum_2025,
title = {Continuum of magnetic excitations in the Kitaev honeycomb iridate D_{3}LiIr_{2}O_{6}},
author = {T. Halloran and Y. Wang and K. W. Plumb and M. B. Stone and B. Winn and M. K. Graves-Brook and J. A. Rodriguez-Rivera and Y. Qui and P. Chauhan and J. Knolle and R. Moessner and N. P. Armitage and T. Takayama and H. Takagi and C. Broholm},
url = {https://www.nature.com/articles/s41535-025-00748-5},
doi = {10.1038/s41535-025-00748-5},
year = {2025},
date = {2025-03-29},
urldate = {2025-03-29},
journal = {npj Quantum Mater.},
volume = {10},
pages = {35},
abstract = {Inelastic neutron scattering (INS) measurements of powder D3LiIr2O6 reveal low energy magnetic excitations with a scattering cross-section that is broad in ∣Q∣ and energy transfer. The magnetic nature of the excitation spectrum is demonstrated by longitudinally polarized neutron scattering. The total magnetic moment of 1.8(4)μB/Ir inferred from the observed magnetic scattering cross-section is consistent with the effective moment inferred from magnetic susceptibility data and expectations for the Jeff = 1/2 single ion state. The rise in the dynamic correlation function S(Q, ω) for ℏω < 5 meV can be described by a simple model assuming nearest-neighbor anisotropic spin exchange, such as that found in the Kitaev model. Exchange disorder associated with the D site likely plays an important role in stabilizing the low T quantum fluctuating state.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Inelastic neutron scattering (INS) measurements of powder D3LiIr2O6 reveal low energy magnetic excitations with a scattering cross-section that is broad in ∣Q∣ and energy transfer. The magnetic nature of the excitation spectrum is demonstrated by longitudinally polarized neutron scattering. The total magnetic moment of 1.8(4)μB/Ir inferred from the observed magnetic scattering cross-section is consistent with the effective moment inferred from magnetic susceptibility data and expectations for the Jeff = 1/2 single ion state. The rise in the dynamic correlation function S(Q, ω) for ℏω < 5 meV can be described by a simple model assuming nearest-neighbor anisotropic spin exchange, such as that found in the Kitaev model. Exchange disorder associated with the D site likely plays an important role in stabilizing the low T quantum fluctuating state. |
