Maria Azhar

Karlsruhe Institute of Technology

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Markus Garst

Karlsruhe Institute of Technology

T. T. M. Palstra

University of Twente

Maxim Mostovoy

University of Groningen

Maxim Mostovoy

University of Groningen

J. Zeisner

Leibniz Institute for Solid State and Materials Research

Machteld E. Kamminga

Utrecht University

Yoshikazu Tabata

Kyoto University

D. Szaller

TU Wien

László Balogh

University of Debrecen

Lisa DeBeer‐Schmitt

Oak Ridge National Laboratory

Cooperative Institutions

University of Groningen

Technical University of Munich

University of Augsburg

Budapest University of Technology and Economics

National Institute for Materials Science

University of Regensburg

Montavid Thermodynamic Research Group

Hungarian Academy of Sciences

Leibniz Institute for Solid State and Materials Research

TU Dresden

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Robust skyrmion-bubble textures in SrRuO3 thin films stabilized by magnetic anisotropy

Physical Review Research (2020)

Ping Zhang Arijit Das Evgenii Barts Maria Azhar Liang Si

The authors show that the stability of magnetic bubbles in materials with strong spin-orbit coupling extends beyond the region predicted by the Kooy-Enz model, when the film thickness becomes comparable to the cylindrical domain wall width.

10.1103/physrevresearch.2.032026

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Citations (23)

Spin-singlet formation in the spin-tetramer layered organic-inorganic hybrid [Formula : see text]

Physical Review Materials (2018)

E Kamminga Machteld Maria Azhar J. Zeisner M C Maan Anna Buechner Bernd

Tetramer

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Squeezing N\'eel-type Magnetic Modulations by Enhanced Dzyaloshinskii-Moriya interaction of $4d$ Electrons

arXiv (Cornell University) (2019)

Ádám Butykai K. Geirhos D. Szaller L. F. Kiss László Balogh

In polar magnets, such as GaV$_4$S$_8$, GaV$_4$Se$_8$ and VOSe$_2$O$_5$, modulated magnetic phases namely the cycloidal and the N\'eel-type skyrmion lattice states were identified over extended temperature ranges, even down to zero Kelvin. Our combined small-angle neutron scattering and magnetization study shows the robustness of the N\'eel-type magnetic modulations also against magnetic fields up to 2 T in the polar GaMo$_4$S$_8$. In addition to the large upper critical field, enhanced spin-orbit coupling produces a variety of modulated phases with sub-10 nm periodicity and a peculiar distribution of the magnetic modulation vectors. Thus, our work demonstrates that non-centrosymmetric magnets with $4d$ and $5d$ electron systems are ideal candidates to host highly compressed magnetic spirals and skyrmions.

Skyrmion

Lattice (music)

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Screw dislocations in cubic chiral magnets

arXiv (Cornell University) (2021)

Maria Azhar Volodymyr P. Kravchuk Markus Garst

Helimagnets realize an effective lamellar ordering that supports disclination and dislocation defects. Here, we investigate the micromagnetic structure of screw dislocation lines in cubic chiral magnets using analytical and numerical methods. The far field of these dislocations is universal and classified by an integer strength $\nu$ that characterizes the winding of magnetic moments. We demonstrate that a rich variety of dislocation-core structures can be realized even for the same strength $\nu$. In particular, the magnetization at the core can be either smooth or singular. We present a specific example with $\nu = 1$ for which the core is composed of a chain of singular Bloch points. In general, screw dislocations carry a non-integer but finite skyrmion charge so that they can be efficiently manipulated by spin currents.

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Disclination

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Squeezing the periodicity of Néel-type magnetic modulations by enhanced Dzyaloshinskii-Moriya interaction of 4d electrons

npj Quantum Materials (2022)

Ádám Butykai K. Geirhos D. Szaller L. F. Kiss László Balogh

Abstract In polar magnets, such as GaV 4 S 8 , GaV 4 Se 8 and VOSe 2 O 5 , modulated magnetic phases namely the cycloidal and the Néel-type skyrmion lattice states were identified over extended temperature ranges, even down to zero Kelvin. Our combined small-angle neutron scattering and magnetization study shows the robustness of the Néel-type magnetic modulations also against magnetic fields up to 2 T in the polar GaMo 4 S 8 . In addition to the large upper critical field, enhanced spin-orbit coupling stabilize cycloidal, Néel skyrmion lattice phases with sub-10 nm periodicity and a peculiar distribution of the magnetic modulation vectors. Moreover, we detected an additional single-q state not observed in any other polar magnets. Thus, our work demonstrates that non-centrosymmetric magnets with 4 d and 5 d electron systems may give rise to various highly compressed modulated states.

Skyrmion

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10.1038/s41535-022-00432-y

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Citations (15)

Spin-singlet formation in the spin-tetramer layered organic-inorganic hybridCH3NH3Cu2Cl5

Physical Review Materials (2018)

Machteld E. Kamminga Maria Azhar J. Zeisner Anna M. C. Maan B. Büchner

We report spin-singlet formation in an organic-inorganic hybrid identified as ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{Cu}}_{2}{\mathrm{Cl}}_{5}$. The hybrid adopts a layered structure in which ${{\mathrm{Cu}}_{2}{\mathrm{Cl}}_{5}}^{\ensuremath{-}}$ layers are separated by ${{\mathrm{CH}}_{3}{\mathrm{NH}}_{3}}^{+}$ layers. The inorganic layers consist of corner- and edge-sharing ${\mathrm{CuCl}}_{6}$ octahedra, forming edge-sharing tetramers. Magnetic susceptibility measurements indicate strong antiferromagnetic interactions within the tetramers, whereas the coupling between the tetramers is weak. Low-temperature magnetic susceptibility data as well as electron spin resonance measurements suggest a nonmagnetic ground state with a large spin gap of $\ensuremath{\sim}130\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, in apparent contradiction with ferromagnetic interactions between nearest-neighbor spins. We discuss a spin-tetramer model in which antiferromagnetic next-nearest-neighbor interactions lead to a spin-singlet state.

Tetramer

Spin states

10.1103/physrevmaterials.2.064405

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CCDC 1839002: Experimental Crystal Structure Determination

The Cambridge Structural Database (2018)

Machteld E. Kamminga Maria Azhar J. Zeisner Anna M. C. Maan B. Büchner

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

10.5517/ccdc.csd.cc1zqmnz

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Incommensurate Spiral Order from Double-Exchange Interactions

Physical Review Letters (2017)

Maria Azhar Maxim Mostovoy

The double-exchange model describing interactions of itinerant electrons with localized spins is usually used to explain ferromagnetism in metals. We show that for a variety of crystal lattices of different dimensionalities and for a wide range of model parameters, the ferromagnetic state is unstable against a noncollinear spiral magnetic order. We revisit the phase diagram of the double-exchange model on a triangular lattice and show in a large part of the diagram the incommensurate spiral state has a lower energy than the previously discussed commensurate states. These results indicate that double-exchange systems are inherently frustrated and can host unconventional spin orders.

Exchange interaction

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Hexagonal Lattice

10.1103/physrevlett.118.027203

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Citations (34)

Screw Dislocations in Chiral Magnets

Physical Review Letters (2022)

Maria Azhar Volodymyr P. Kravchuk Markus Garst

Helimagnets realize an effective lamellar ordering that supports disclination and dislocation defects. Here, we investigate the micromagnetic structure of screw dislocation lines in cubic chiral magnets using analytical and numerical methods. The far field of these dislocations is universal and classified by an integer strength ν that quantifies its Burgers vector. We demonstrate that a rich variety of dislocation-core structures can be realized even for the same strength ν. In particular, the magnetization at the core can be either smooth or singular. We present a specific example with ν=1 for which the core is composed of a chain of singular Bloch points. In general, screw dislocations carry a noninteger but finite skyrmion charge so that they can be efficiently manipulated by spin currents and should contribute to the topological Hall effect.

Skyrmion

Disclination

Burgers vector

Topological defect

10.1103/physrevlett.128.157204

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Citations (13)

All-electrical detection of skyrmion lattice state and chiral surface twists

Physical review. B./Physical review. B (2021)

Aisha Aqeel Maria Azhar N. Vlietstra Alessio Pozzi Jan Sahliger

We study the high-temperature phase diagram of the chiral magnetic insulator ${\mathrm{Cu}}_{2}\mathrm{O}\mathrm{Se}{\mathrm{O}}_{3}$ by measuring the spin-Hall magnetoresistance (SMR) in a thin Pt electrode. We find distinct changes in the phase and amplitude of the SMR signal at critical lines separating different magnetic phases of bulk ${\mathrm{Cu}}_{2}\mathrm{O}\mathrm{Se}{\mathrm{O}}_{3}$. The skyrmion lattice state appears as a strong dip in the SMR phase. A strong enhancement of the SMR amplitude is observed in the conical spiral state, which we explain by an additional symmetry-allowed contribution to the SMR present in noncollinear magnets. We demonstrate that the SMR can be used as an all-electrical probe of chiral surface twists and skyrmions in magnetic insulators.

Skyrmion

Lattice (music)

10.1103/physrevb.103.l100410

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Citations (9)