Uwe Stuhr

Paul Scherrer Institute

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Paul Scherrer Institute

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Technische Universität Darmstadt

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Uwe Stuhr has a total of 135 co-authors. Here are the top co-authors by number of shared publications:

Jakob Lass
Paul Scherrer Institute
3 shared publications
Kim Lefmann
Nanoscience Center, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
3 shared publications
Bertrand Roessli
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen, Switzerland
2 shared publications
Christof Niedermayer
Paul Scherrer Institute
2 shared publications
Henrik Moodysson Rønnow
École Polytechnique Fédérale de Lausanne (EPFL)
2 shared publications
Je-Geun Park
Department of Physics and Astronomy, Seoul National University, Seoul, Republic of Korea
2 shared publications

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- 24 April 2026
- Published by Springer Nature in Research Square
Field-induced quasi-bound state within the two-magnon continuum of a square-lattice Heisenberg antiferromagnet
by Martin Mansson, Frank Elson, Mithilesh Nayak, Alexander Eberharter, Markos Skoulatos, Simon Ward, Uwe Stuhr, Niels Christensen, David Voneshen, Christoph Fiolka, et al.
Quantum magnets in two dimensions display strong quantum interaction effects even when magnetically ordered. Using the metal-organic framework material CuF ₂ (D ₂ O) ₂ (pyz), we investigate the field-dependent spin dynamics of the S = 1/2 square-lattice Heisenberg antiferromagnet by high-resolution inelastic neutron scattering to applied fields beyond one third of saturation. We discover an anomalously sharp, dispersive “shadow mode” residing within the two-magnon continuum, which shadows the dispersion of the transverse one-magnon branches across the Brillouin zone at an offset equal to the Larmor energy. We perform cylinder matrix-product-state (MPS) calculations that reproduce the field-induced spectrum quantitatively and apply a spectrally consistent 1/ S spin-wave theory to deduce that the “Larmor-shadow mode” is a composite two-magnon resonance: a dispersing magnon at wavevector Q couples to the uniform Larmor precession at Γ, its small intrinsic linewidth indicating a non-perturbative effect of attractive magnon-magnon interactions. Another quantum-fluctuation phenomenon, the zero-field (π, 0) anomaly, is lost at increasing fields, which tighten the spectral weight into the one-magnon and Larmor-shadow modes. To our knowledge, these results constitute the first observation of a sharp quasi-bound state embedded in the continuum of a gapless two-dimensional antiferromagnet.
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- 24 April 2026
- Published by Springer Nature in Research Square
Open Access
Field-induced quasi-bound state within the two-magnon continuum of a square-lattice Heisenberg antiferromagnet
by Martin Mansson, Frank Elson, Mithilesh Nayak, Alexander Eberharter, Markos Skoulatos, Simon Ward, Uwe Stuhr, Niels Christensen, David Voneshen, Christoph Fiolka, et al.
Quantum magnets in two dimensions display strong quantum interaction effects even when magnetically ordered. Using the metal-organic framework material CuF ₂ (D ₂ O) ₂ (pyz), we investigate the field-dependent spin dynamics of the S = 1/2 square-lattice Heisenberg antiferromagnet by high-resolution inelastic neutron scattering to applied fields beyond one third of saturation. We discover an anomalously sharp, dispersive “shadow mode” residing within the two-magnon continuum, which shadows the dispersion of the transverse one-magnon branches across the Brillouin zone at an offset equal to the Larmor energy. We perform cylinder matrix-product-state (MPS) calculations that reproduce the field-induced spectrum quantitatively and apply a spectrally consistent 1/ S spin-wave theory to deduce that the “Larmor-shadow mode” is a composite two-magnon resonance: a dispersing magnon at wavevector Q couples to the uniform Larmor precession at Γ, its small intrinsic linewidth indicating a non-perturbative effect of attractive magnon-magnon interactions. Another quantum-fluctuation phenomenon, the zero-field (π, 0) anomaly, is lost at increasing fields, which tighten the spectral weight into the one-magnon and Larmor-shadow modes. To our knowledge, these results constitute the first observation of a sharp quasi-bound state embedded in the continuum of a gapless two-dimensional antiferromagnet.
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Cited by 2
- 16 January 2026
- Published by American Physical Society (APS) in Physical Review B
Refined spin Hamiltonian on the Cairo pentagonal lattice of Bi 2 Fe 4 O 9
by Emma Y. Lenander, Frida B. Nielsen, Jakob Lass, Ursula B. Hansen, Kristine M. L. Krighaar, Asbjørn Preuss, Tobias Weber, Mechthild Enderle, Henrik Jacobsen, Uwe Stuhr, et al.
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- 16 January 2026
- Published by American Physical Society (APS) in Physical Review B
Refined spin Hamiltonian on the Cairo pentagonal lattice of Bi 2 Fe 4 O 9
by Emma Y. Lenander, Frida B. Nielsen, Jakob Lass, Ursula B. Hansen, Kristine M. L. Krighaar, Asbjørn Preuss, Tobias Weber, Mechthild Enderle, Henrik Jacobsen, Uwe Stuhr, et al.
Cited by 2
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Cited by 1
- 23 January 2024
- Published by American Physical Society (APS) in Physical Review B
Influence of ${Dy}^{3 +}$ environment on magnetic anisotropy and magnetocaloric effect in ${Dy}_{3} B_{2} C_{3} O_{12}$ $(B = In, Sc, Te; C = Ga, Al, Li)$ garnets
by F. Damay, S. Petit, D. Sheptyakov, C. V. Colin, E. Suard, S. Rols, J. Embs, U. Stuhr, D. Bounoua, O. Demortier, et al.
In the framework of the general phase diagram published recently for a pseudospin $S = 1 / 2$ on a hyperkagome network [Kibalin et al., Phys. Rev. Res. 2, 033509 (2020)], four ${Dy}_{3} B_{2} C_{3} O_{12}$ garnets with different species on the $B$ and $C$ sites, namely, ${Dy}_{3} {Sc}_{2} {Al}_{3} O_{12}$ (DyScAl), ${Dy}_{3} {Te}_{2} {Li}_{3} O_{12}$ (DyTeLi), ${Dy}_{3} {Sc}_{2} {Ga}_{3} O_{12}$ (DyScGa), and ${Dy}_{3} {In}_{2} {Ga}_{3} O_{12}$ (DyInGa), have been studied by neutron powder diffraction and inelastic neutron scattering, to investigate the impact of $B$ and $C$ substitutions on the ${Dy}^{3 +}$ dodecahedral oxygen environment and crystal field, and thus on the ${Dy}^{3 +}$ spin magnetic anisotropy. In the four compounds, the magnetic ground state is a multiaxis antiferromagnetic order similar to that of ${Dy}_{3} {Al}_{5} O_{12}$ , characterized by an ordered moment close to the theoretical maximum, $\sim 6 µ_{B}$ . The gap between the ground state and the first excited crystal electric field level varies from $\sim 3.2$ meV (DyInGa) up to 11.2 meV (DyScAl), confirming the rather strong Ising character of the ${Dy}^{3 +}$ moment in those garnets. For a better understanding of the impact of the distortion of the oxygen environment on the ${Dy}^{3 +}$ magnetic anisotropy, point-charge calculations were then performed, mapping a magnetic anisotropy diagram versus a wide range of distortions. Results show that Ising-like behaviors mostly predominate, associated with large $g_{x}, g_{y}$ , or $g_{z}$ Landé values, whose stable area is determined by the shape of the $Dy O_{8}$ cage. Magnetic entropy calculations confirm that the magnetocaloric effect increases sharply near those boundaries and validate the use of dysprosium garnets for low temperature, low magnetic field adiabatic demagnetization refrigeration cryostats.
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- 23 January 2024
- Published by American Physical Society (APS) in Physical Review B
Influence of ${Dy}^{3 +}$ environment on magnetic anisotropy and magnetocaloric effect in ${Dy}_{3} B_{2} C_{3} O_{12}$ $(B = In, Sc, Te; C = Ga, Al, Li)$ garnets
by F. Damay, S. Petit, D. Sheptyakov, C. V. Colin, E. Suard, S. Rols, J. Embs, U. Stuhr, D. Bounoua, O. Demortier, et al.
In the framework of the general phase diagram published recently for a pseudospin $S = 1 / 2$ on a hyperkagome network [Kibalin et al., Phys. Rev. Res. 2, 033509 (2020)], four ${Dy}_{3} B_{2} C_{3} O_{12}$ garnets with different species on the $B$ and $C$ sites, namely, ${Dy}_{3} {Sc}_{2} {Al}_{3} O_{12}$ (DyScAl), ${Dy}_{3} {Te}_{2} {Li}_{3} O_{12}$ (DyTeLi), ${Dy}_{3} {Sc}_{2} {Ga}_{3} O_{12}$ (DyScGa), and ${Dy}_{3} {In}_{2} {Ga}_{3} O_{12}$ (DyInGa), have been studied by neutron powder diffraction and inelastic neutron scattering, to investigate the impact of $B$ and $C$ substitutions on the ${Dy}^{3 +}$ dodecahedral oxygen environment and crystal field, and thus on the ${Dy}^{3 +}$ spin magnetic anisotropy. In the four compounds, the magnetic ground state is a multiaxis antiferromagnetic order similar to that of ${Dy}_{3} {Al}_{5} O_{12}$ , characterized by an ordered moment close to the theoretical maximum, $\sim 6 µ_{B}$ . The gap between the ground state and the first excited crystal electric field level varies from $\sim 3.2$ meV (DyInGa) up to 11.2 meV (DyScAl), confirming the rather strong Ising character of the ${Dy}^{3 +}$ moment in those garnets. For a better understanding of the impact of the distortion of the oxygen environment on the ${Dy}^{3 +}$ magnetic anisotropy, point-charge calculations were then performed, mapping a magnetic anisotropy diagram versus a wide range of distortions. Results show that Ising-like behaviors mostly predominate, associated with large $g_{x}, g_{y}$ , or $g_{z}$ Landé values, whose stable area is determined by the shape of the $Dy O_{8}$ cage. Magnetic entropy calculations confirm that the magnetocaloric effect increases sharply near those boundaries and validate the use of dysprosium garnets for low temperature, low magnetic field adiabatic demagnetization refrigeration cryostats.
Cited by 1
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Cited by 11
- 21 June 2023
- Published by American Physical Society (APS) in Physical Review B
Interlayer coupling in the superconducting state of iron-based superconductors
by Wenshan Hong, Honglin Zhou, Zezhong Li, Yang Li, Uwe Stuhr, Amit Pokhriyal, Haranath Ghosh, Zhen Tao, Xingye Lu, Jiangping Hu, et al.
High-temperature superconducting paring is generally believed to be mediated by the magnetic fluctuations that mostly occur within the two-dimensional conducting layers (Cu-O, Fe-As, or Fe-Se) in copper oxides, iron pnictides, iron chalcogenides, etc. Here, on the basis of inelastic neutron scattering measurements on a superconducting iron pnictide ${Ca}_{0.33} {Na}_{0.67} {Fe}_{2} {As}_{2}$ , we have discovered a highly three-dimensional spin resonance mode with upward V-shape dispersions both in the $a b$ plane and along the $c$ axis. The superconducting gaps exhibit strong $k_{z}$ modulations involved with significant changes on the size of one hole pocket and the density state of the $d_{z^{2}}$ orbital of Fe. The resonance dispersions don't always seem confined by the total gaps summed on those imperfectly nesting Fermi sheets. It is demonstrated that the $c$ -axis dependence of both the resonance energy and its intensity in iron pnictides can be universally scaled with the distance between two adjacent Fe-As layers ( $d$ ), and the $k_{z}$ modulation of the gap is also anticorrelated with $d$ . These results highlight the role of interlayer coupling in iron-based superconductivity, suggesting that the interlayer pairing may also be driven by magnetic fluctuations under certain spin-orbit couplings.
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- 21 June 2023
- Published by American Physical Society (APS) in Physical Review B
Interlayer coupling in the superconducting state of iron-based superconductors
by Wenshan Hong, Honglin Zhou, Zezhong Li, Yang Li, Uwe Stuhr, Amit Pokhriyal, Haranath Ghosh, Zhen Tao, Xingye Lu, Jiangping Hu, et al.
High-temperature superconducting paring is generally believed to be mediated by the magnetic fluctuations that mostly occur within the two-dimensional conducting layers (Cu-O, Fe-As, or Fe-Se) in copper oxides, iron pnictides, iron chalcogenides, etc. Here, on the basis of inelastic neutron scattering measurements on a superconducting iron pnictide ${Ca}_{0.33} {Na}_{0.67} {Fe}_{2} {As}_{2}$ , we have discovered a highly three-dimensional spin resonance mode with upward V-shape dispersions both in the $a b$ plane and along the $c$ axis. The superconducting gaps exhibit strong $k_{z}$ modulations involved with significant changes on the size of one hole pocket and the density state of the $d_{z^{2}}$ orbital of Fe. The resonance dispersions don't always seem confined by the total gaps summed on those imperfectly nesting Fermi sheets. It is demonstrated that the $c$ -axis dependence of both the resonance energy and its intensity in iron pnictides can be universally scaled with the distance between two adjacent Fe-As layers ( $d$ ), and the $k_{z}$ modulation of the gap is also anticorrelated with $d$ . These results highlight the role of interlayer coupling in iron-based superconductivity, suggesting that the interlayer pairing may also be driven by magnetic fluctuations under certain spin-orbit couplings.
Cited by 11
Open Access
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Cited by 27
- 19 April 2023
- Published by Springer Nature in Nature Communications
Active learning-assisted neutron spectroscopy with log-Gaussian processes
by Mario Teixeira Parente, Georg Brandl, Christian Franz, Uwe Stuhr, Marina Ganeva, Astrid Schneidewind
Neutron scattering experiments at three-axes spectrometers (TAS) investigate magnetic and lattice excitations by measuring intensity distributions to understand the origins of materials properties. The high demand and limited availability of beam time for TAS experiments however raise the natural question whether we can improve their efficiency and make better use of the experimenter’s time. In fact, there are a number of scientific problems that require searching for signals, which may be time consuming and inefficient if done manually due to measurements in uninformative regions. Here, we describe a probabilistic active learning approach that not only runs autonomously, i.e., without human interference, but can also directly provide locations for informative measurements in a mathematically sound and methodologically robust way by exploiting log-Gaussian processes. Ultimately, the resulting benefits can be demonstrated on a real TAS experiment and a benchmark including numerous different excitations.
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- 19 April 2023
- Published by Springer Nature in Nature Communications
Open Access
Active learning-assisted neutron spectroscopy with log-Gaussian processes
by Mario Teixeira Parente, Georg Brandl, Christian Franz, Uwe Stuhr, Marina Ganeva, Astrid Schneidewind
Neutron scattering experiments at three-axes spectrometers (TAS) investigate magnetic and lattice excitations by measuring intensity distributions to understand the origins of materials properties. The high demand and limited availability of beam time for TAS experiments however raise the natural question whether we can improve their efficiency and make better use of the experimenter’s time. In fact, there are a number of scientific problems that require searching for signals, which may be time consuming and inefficient if done manually due to measurements in uninformative regions. Here, we describe a probabilistic active learning approach that not only runs autonomously, i.e., without human interference, but can also directly provide locations for informative measurements in a mathematically sound and methodologically robust way by exploiting log-Gaussian processes. Ultimately, the resulting benefits can be demonstrated on a real TAS experiment and a benchmark including numerous different excitations.
Cited by 27
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Cited by 6
- 21 February 2023
- Published by American Physical Society (APS) in Physical Review Materials
Evidence of correlated incommensurate structural and magnetic order in highly oxygen-doped layered nickelate ${Nd}_{2} {NiO}_{4.23}$
by Sumit Ranjan Maity, Monica Ceretti, Lukas Keller, Jürg Schefer, Bertrand Roessli, Uwe Stuhr, Christof Niedermayer, Werner Paulus
$Nd_{2} NiO_{4 + δ}$ is a nonstoichiometric oxide, crystallizing in the Ruddlesden-Popper-type framework and exhibiting a wide range of oxygen nonstoichiometry $δ$ with a complex structural phase diagram. Excess oxygen atoms insert holes, directly influencing the Ni valence state and associated electronic structure. We report here the existence of a correlated incommensurate structural and antiferromagnetic order below $T_{N} \approx$ 150 K in highly oxygen-doped $Nd_{2} NiO_{4 + δ}$ with $δ \approx$ 0.23. The crystal and magnetic structures are investigated by polarized and unpolarized single-crystal neutron diffraction studies together with synchrotron x-ray powder diffraction and macroscopic magnetization measurements. Due to the long-range ordering of excess oxygen atoms, the real structure of the compound is incommensurately modulated, represented by $Q_{n} = \pm 0.813 a^{*} \pm 0.519 b^{*}$ wave vectors. The antiferromagnetic order is characterized by the presence of incommensurate Bragg peaks of type ( $h \pm ɛ$ , 0, $l$ /2), with $h$ and $l$ being odd-integer numbers and the magnetic incommensurability $ɛ \approx$ 0.36. The in-plane magnetic correlation length is found to be $ξ_{a b}$ = 184(1) Å but is significantly reduced along the $c$ axis to $ξ_{c}$ = 39(2) Å, indicating the quasi-two-dimensional nature of the antiferromagnetic correlations. Our study indicates that the excess oxygen atoms nevertheless strongly enhance the magnetic correlations between the ${NiO}_{2}$ planes, resulting in a doubling of the magnetic unit cell along the $c$ axis. In contrast to $Nd_{2} NiO_{4.1}$ , in which the incommensurate periodicity of oxygen and magnetic ordering was found to be identical, the structural and electronic orderings in heavily oxygen-doped ${Nd}_{2} {NiO}_{4.23}$ show two independent modulation vectors. Our study thus unravels a strong correlation between structural and electronic orderings in the highly oxygen-doped $Ln_{2} NiO_{4 + δ}$ system.
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- 21 February 2023
- Published by American Physical Society (APS) in Physical Review Materials
Evidence of correlated incommensurate structural and magnetic order in highly oxygen-doped layered nickelate ${Nd}_{2} {NiO}_{4.23}$
by Sumit Ranjan Maity, Monica Ceretti, Lukas Keller, Jürg Schefer, Bertrand Roessli, Uwe Stuhr, Christof Niedermayer, Werner Paulus
$Nd_{2} NiO_{4 + δ}$ is a nonstoichiometric oxide, crystallizing in the Ruddlesden-Popper-type framework and exhibiting a wide range of oxygen nonstoichiometry $δ$ with a complex structural phase diagram. Excess oxygen atoms insert holes, directly influencing the Ni valence state and associated electronic structure. We report here the existence of a correlated incommensurate structural and antiferromagnetic order below $T_{N} \approx$ 150 K in highly oxygen-doped $Nd_{2} NiO_{4 + δ}$ with $δ \approx$ 0.23. The crystal and magnetic structures are investigated by polarized and unpolarized single-crystal neutron diffraction studies together with synchrotron x-ray powder diffraction and macroscopic magnetization measurements. Due to the long-range ordering of excess oxygen atoms, the real structure of the compound is incommensurately modulated, represented by $Q_{n} = \pm 0.813 a^{*} \pm 0.519 b^{*}$ wave vectors. The antiferromagnetic order is characterized by the presence of incommensurate Bragg peaks of type ( $h \pm ɛ$ , 0, $l$ /2), with $h$ and $l$ being odd-integer numbers and the magnetic incommensurability $ɛ \approx$ 0.36. The in-plane magnetic correlation length is found to be $ξ_{a b}$ = 184(1) Å but is significantly reduced along the $c$ axis to $ξ_{c}$ = 39(2) Å, indicating the quasi-two-dimensional nature of the antiferromagnetic correlations. Our study indicates that the excess oxygen atoms nevertheless strongly enhance the magnetic correlations between the ${NiO}_{2}$ planes, resulting in a doubling of the magnetic unit cell along the $c$ axis. In contrast to $Nd_{2} NiO_{4.1}$ , in which the incommensurate periodicity of oxygen and magnetic ordering was found to be identical, the structural and electronic orderings in heavily oxygen-doped ${Nd}_{2} {NiO}_{4.23}$ show two independent modulation vectors. Our study thus unravels a strong correlation between structural and electronic orderings in the highly oxygen-doped $Ln_{2} NiO_{4 + δ}$ system.
Cited by 6
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Cited by 8
- 16 July 2022
- Published by Springer Nature in Communications Physics
Dipolar spin-waves and tunable band gap at the Dirac points in the 2D magnet ErBr3
by Christian Wessler, Bertrand Roessli, Karl W. Krämer, Uwe Stuhr, Andrew Wildes, Hans B. Braun, Michel Kenzelmann
Topological magnon insulators constitute a growing field of research for their potential use as information carriers without heat dissipation. We report an experimental and theoretical study of the magnetic ground-state and excitations in the van der Waals two-dimensional honeycomb magnet ErBr₃. We show that the magnetic properties of this compound are entirely governed by the dipolar interactions which generate a continuously degenerate non-collinear ground-state on the honeycomb lattice with spins confined in the plane. We find that the magnon dispersion exhibits Dirac-like cones when the magnetic moments in the ground-state are related by time-reversal and inversion symmetries associated with a Berry phaseπas in single-layer graphene. A magnon band gap opens when the dipoles are rotated away from this state, entailing a finite Berry curvature in the vicinity of the K and K’ Dirac points. Our results illustrate that the spin-wave dispersion of dipoles on the honeycomb lattice can be reversibly controlled from a magnetic phase with Dirac cones to a topological antiferromagnetic insulator with non-trivial valley Chern number.
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- 16 July 2022
- Published by Springer Nature in Communications Physics
Open Access
Dipolar spin-waves and tunable band gap at the Dirac points in the 2D magnet ErBr3
by Christian Wessler, Bertrand Roessli, Karl W. Krämer, Uwe Stuhr, Andrew Wildes, Hans B. Braun, Michel Kenzelmann
Topological magnon insulators constitute a growing field of research for their potential use as information carriers without heat dissipation. We report an experimental and theoretical study of the magnetic ground-state and excitations in the van der Waals two-dimensional honeycomb magnet ErBr₃. We show that the magnetic properties of this compound are entirely governed by the dipolar interactions which generate a continuously degenerate non-collinear ground-state on the honeycomb lattice with spins confined in the plane. We find that the magnon dispersion exhibits Dirac-like cones when the magnetic moments in the ground-state are related by time-reversal and inversion symmetries associated with a Berry phaseπas in single-layer graphene. A magnon band gap opens when the dipoles are rotated away from this state, entailing a finite Berry curvature in the vicinity of the K and K’ Dirac points. Our results illustrate that the spin-wave dispersion of dipoles on the honeycomb lattice can be reversibly controlled from a magnetic phase with Dirac cones to a topological antiferromagnetic insulator with non-trivial valley Chern number.
Cited by 8
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Cited by 68
- 14 April 2022
- Published by American Physical Society (APS) in Physical Review B
Anisotropy of the magnetic and transport properties of ${EuZn}_{2} {As}_{2}$
by Zhi-Cheng Wang, Emily Been, Jonathan Gaudet, Gadeer Matook A. Alqasseri, Kyle Fruhling, Xiaohan Yao, Uwe Stuhr, Qinqing Zhu, Zhi Ren, Yi Cui, et al.
Several recent studies have shown that the anisotropy in the magnetic structure of ${EuCd}_{2} {As}_{2}$ plays a significant role in stabilizing the Weyl nodes. To investigate the relationship between magnetic anisotropy and Weyl physics, we present a comparative study between ${EuZn}_{2} {As}_{2}$ and ${EuCd}_{2} {As}_{2}$ that are isostructural but with different magnetic anisotropy. We performed structural analysis, electronic transport, and magnetization experiments on millimeter-sized single crystals of ${EuZn}_{2} {As}_{2}$ , and compared the results to those of ${EuCd}_{2} {As}_{2}$ . By combining the first principle calculations and neutron diffraction experiment, we identify the magnetic ground state of ${EuZn}_{2} {As}_{2}$ as A-type antiferromagnetic order with a transition temperature ( $T_{N}$ = 19.6 K) twice that of ${EuCd}_{2} {As}_{2}$ . Like ${EuCd}_{2} {As}_{2}$ , the negative magnetoresistance of ${EuZn}_{2} {As}_{2}$ is observed after suppressing the resistivity peak at $T_{N}$ with increasing fields. However, the anisotropy in both transport and magnetization are much reduced in ${EuZn}_{2} {As}_{2}$ . The difference could be ascribed to the weaker spin-orbit coupling, more localized $d$ orbitals, and a larger contribution from the Eu $s$ orbitals in the zinc compound, as suggested by the electronic band calculations. The same band structure effect could be also responsible for the observation of a smaller nonlinear anomalous Hall effect in ${EuZn}_{2} {As}_{2}$ compared to ${EuCd}_{2} {As}_{2}$ .
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- 14 April 2022
- Published by American Physical Society (APS) in Physical Review B
Anisotropy of the magnetic and transport properties of ${EuZn}_{2} {As}_{2}$
by Zhi-Cheng Wang, Emily Been, Jonathan Gaudet, Gadeer Matook A. Alqasseri, Kyle Fruhling, Xiaohan Yao, Uwe Stuhr, Qinqing Zhu, Zhi Ren, Yi Cui, et al.
Several recent studies have shown that the anisotropy in the magnetic structure of ${EuCd}_{2} {As}_{2}$ plays a significant role in stabilizing the Weyl nodes. To investigate the relationship between magnetic anisotropy and Weyl physics, we present a comparative study between ${EuZn}_{2} {As}_{2}$ and ${EuCd}_{2} {As}_{2}$ that are isostructural but with different magnetic anisotropy. We performed structural analysis, electronic transport, and magnetization experiments on millimeter-sized single crystals of ${EuZn}_{2} {As}_{2}$ , and compared the results to those of ${EuCd}_{2} {As}_{2}$ . By combining the first principle calculations and neutron diffraction experiment, we identify the magnetic ground state of ${EuZn}_{2} {As}_{2}$ as A-type antiferromagnetic order with a transition temperature ( $T_{N}$ = 19.6 K) twice that of ${EuCd}_{2} {As}_{2}$ . Like ${EuCd}_{2} {As}_{2}$ , the negative magnetoresistance of ${EuZn}_{2} {As}_{2}$ is observed after suppressing the resistivity peak at $T_{N}$ with increasing fields. However, the anisotropy in both transport and magnetization are much reduced in ${EuZn}_{2} {As}_{2}$ . The difference could be ascribed to the weaker spin-orbit coupling, more localized $d$ orbitals, and a larger contribution from the Eu $s$ orbitals in the zinc compound, as suggested by the electronic band calculations. The same band structure effect could be also responsible for the observation of a smaller nonlinear anomalous Hall effect in ${EuZn}_{2} {As}_{2}$ compared to ${EuCd}_{2} {As}_{2}$ .
Cited by 68
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Cited by 14
- 17 March 2021
- Published by American Physical Society (APS) in Physical Review B
Magnetic order in the quasi-one-dimensional Ising system $RbCo {Cl}_{3}$
by N. P. Hänni, D. Sheptyakov, M. Mena, E. Hirtenlechner, L. Keller, U. Stuhr, L.-P. Regnault, M. Medarde, A. Cervellino, Ch. Rüegg, et al.
In $RbCo {Cl}_{3}$ , the magnetic ${Co}^{2 +}$ ions form weakly coupled Ising chains arranged on a triangular lattice. We have investigated the structure and magnetism in $RbCo {Cl}_{3}$ by high-resolution x-ray diffraction and neutron scattering measurements on powder and single-crystal samples between 1.5 and 300 K. Upon cooling, the ${Co}^{2 +}$ spins develop one-dimensional antiferromagnetic correlations along the chain axis ( $c$ axis) below 90 K. Below the first Néel temperature, $T_{N 1} = 28 K$ , a partial three-dimensional magnetic order sets in, with propagation vector $k_{1} = (1 / 3, 1 / 3, 1)$ , the moments aligned along the $c$ axis, and every third chain uncorrelated from its neighbors. Only below a second magnetic phase transition at $T_{N 2} = 13 K$ does the system achieve a fully ordered state, with two additional propagation vectors: $k_{2} = (0, 0, 1)$ establishes a “honeycomb” $c$ -axis order, in which one third of the chains are subject to a strong effective mean field due to their neighbors whereas two thirds experience no net field, while $k_{3} = (1 / 2, 0, 1)$ governs a small, staggered, in-plane ordered moment. We conclude that $RbCo {Cl}_{3}$ is an excellent material to study the physics of Ising chains in a wide variety of temperature-controlled environments, and our results build an important foundation for the accurate interpretation of the spin dynamics measured in each case.
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- 17 March 2021
- Published by American Physical Society (APS) in Physical Review B
Magnetic order in the quasi-one-dimensional Ising system $RbCo {Cl}_{3}$
by N. P. Hänni, D. Sheptyakov, M. Mena, E. Hirtenlechner, L. Keller, U. Stuhr, L.-P. Regnault, M. Medarde, A. Cervellino, Ch. Rüegg, et al.
In $RbCo {Cl}_{3}$ , the magnetic ${Co}^{2 +}$ ions form weakly coupled Ising chains arranged on a triangular lattice. We have investigated the structure and magnetism in $RbCo {Cl}_{3}$ by high-resolution x-ray diffraction and neutron scattering measurements on powder and single-crystal samples between 1.5 and 300 K. Upon cooling, the ${Co}^{2 +}$ spins develop one-dimensional antiferromagnetic correlations along the chain axis ( $c$ axis) below 90 K. Below the first Néel temperature, $T_{N 1} = 28 K$ , a partial three-dimensional magnetic order sets in, with propagation vector $k_{1} = (1 / 3, 1 / 3, 1)$ , the moments aligned along the $c$ axis, and every third chain uncorrelated from its neighbors. Only below a second magnetic phase transition at $T_{N 2} = 13 K$ does the system achieve a fully ordered state, with two additional propagation vectors: $k_{2} = (0, 0, 1)$ establishes a “honeycomb” $c$ -axis order, in which one third of the chains are subject to a strong effective mean field due to their neighbors whereas two thirds experience no net field, while $k_{3} = (1 / 2, 0, 1)$ governs a small, staggered, in-plane ordered moment. We conclude that $RbCo {Cl}_{3}$ is an excellent material to study the physics of Ising chains in a wide variety of temperature-controlled environments, and our results build an important foundation for the accurate interpretation of the spin dynamics measured in each case.
Cited by 14
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Cited by 6
- 16 March 2021
- Published by American Physical Society (APS) in Physical Review B
Experimental determination of the magnetic interactions of frustrated Cairo pentagon lattice materials
by Manh Duc Le, Elisa M. Wheeler, Jaehong Jeong, K. Ramesh Kumar, Seongsu Lee, Chang-Hee Lee, Myeong Jun Oh, Youn-Jung Jo, Akihiro Kondo, Koichi Kindo, et al.
We present inelastic neutron scattering measurements of the Cairo pentagon lattice magnets ${Bi}_{2} {Fe}_{4} O_{9}$ and ${Bi}_{4} {Fe}_{5} O_{13} F$ , supported by high field magnetization measurements of ${Bi}_{2} {Fe}_{4} O_{9}$ . Using linear spin wave theory and mean-field analyses we determine the spin exchange interactions and single-ion anisotropy in these materials. The Cairo lattice is geometrically frustrated and consists of two inequivalent magnetic sites, both occupied by ${Fe}^{3 +}$ ions and connected by two competing nearest neighbor interactions. We found that one of these interactions, coupling nearest neighbor spins on the threefold symmetric sites, is extremely strong and antiferromagnetic. These strongly coupled dimers are then weakly coupled to a framework formed from spins occupying the other inequivalent site. In addition, we found that the ${Fe}^{3 +} S = 5 / 2$ spins have a non-negligible single-ion anisotropy, which manifests as a spin anisotropy gap in the neutron spectrum and a spin-flop transition in high field magnetization measurements.
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- 16 March 2021
- Published by American Physical Society (APS) in Physical Review B
Open Access
Experimental determination of the magnetic interactions of frustrated Cairo pentagon lattice materials
by Manh Duc Le, Elisa M. Wheeler, Jaehong Jeong, K. Ramesh Kumar, Seongsu Lee, Chang-Hee Lee, Myeong Jun Oh, Youn-Jung Jo, Akihiro Kondo, Koichi Kindo, et al.
We present inelastic neutron scattering measurements of the Cairo pentagon lattice magnets ${Bi}_{2} {Fe}_{4} O_{9}$ and ${Bi}_{4} {Fe}_{5} O_{13} F$ , supported by high field magnetization measurements of ${Bi}_{2} {Fe}_{4} O_{9}$ . Using linear spin wave theory and mean-field analyses we determine the spin exchange interactions and single-ion anisotropy in these materials. The Cairo lattice is geometrically frustrated and consists of two inequivalent magnetic sites, both occupied by ${Fe}^{3 +}$ ions and connected by two competing nearest neighbor interactions. We found that one of these interactions, coupling nearest neighbor spins on the threefold symmetric sites, is extremely strong and antiferromagnetic. These strongly coupled dimers are then weakly coupled to a framework formed from spins occupying the other inequivalent site. In addition, we found that the ${Fe}^{3 +} S = 5 / 2$ spins have a non-negligible single-ion anisotropy, which manifests as a spin anisotropy gap in the neutron spectrum and a spin-flop transition in high field magnetization measurements.
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