Ondrej Sipr
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Previous Organizations / Institutes
The organizations / institutes from the scholar's other articles in the past ten years
Research Subjects
Research Interests
Ondrej Sipr has a total of 163 co-authors. Here are the top co-authors by number of shared publications:
- Jan Minar
University of West Bohemia in Pilsen
24 shared publications H. Ebert
Department of Chemistry, Ludwig-Maximilians-Universität München Butenandtstr. 11, D-81377 München, Germany
17 shared publications- Jiří Vackář
Institute of Physics Academy of Sciences of the Czech Republic Na Slovance 2 182 21 Praha 8 Czech Republic
16 shared publications - Antonin Simunek
Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Praha 8, Czech Republic
14 shared publications Hubert Ebert
Department of Chemistry, Ludwig-Maximilians-University Munich, Butenandtstrasse 11, D-81377 Munich, Germany
13 shared publications- Francesco Rocca
IFN-CNR, Institute for Photonics and Nanotechnologies, Unit FBK-Photonics of Trento, Povo, Trento, Italy
9 shared publications
Latest Publications
- Open Access
- 4 November 2024
- Published by American Physical Society (APS) in Physical Review B
- Vol. 110 (17)
Role of pressure-induced stacking faults on the magnetic properties of gadolinium
Experimental data show that under pressure, Gd goes through a series of structural transitions hcp → Sm -type (close-packed rhombohedral) → dhcp that is accompanied by a gradual decrease of the Curie temperature and magnetization till the collapse of a finite magnetization close to the dhcp structure. We explore theoretically the pressure-induced changes of the magnetic properties, by describing these structural transitions as the formation of fcc stacking faults. Using this approach, we are able to describe correctly the variation of the Curie temperature with pressure, in contrast to a static structural model using the hcp structure. Published by the American Physical Society 2024
- 4 November 2024
- Published by American Physical Society (APS) in Physical Review B
- Vol. 110 (17)
Open AccessRole of pressure-induced stacking faults on the magnetic properties of gadolinium
Experimental data show that under pressure, Gd goes through a series of structural transitions hcp → Sm -type (close-packed rhombohedral) → dhcp that is accompanied by a gradual decrease of the Curie temperature and magnetization till the collapse of a finite magnetization close to the dhcp structure. We explore theoretically the pressure-induced changes of the magnetic properties, by describing these structural transitions as the formation of fcc stacking faults. Using this approach, we are able to describe correctly the variation of the Curie temperature with pressure, in contrast to a static structural model using the hcp structure. Published by the American Physical Society 2024
- Top Cited Papers
- 20 December 2023
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 131 (25) , 256703
Chiral Magnons in AltermagneticMagnons in ferromagnets have one chirality, and typically are in the GHz range and have a quadratic dispersion near the zero wave vector. In contrast, magnons in antiferromagnets are commonly considered to have bands with both chiralities that are degenerate across the entire Brillouin zone, and to be in the THz range and to have a linear dispersion near the center of the Brillouin zone. Here we theoretically demonstrate a new class of magnons on a prototypical -wave altermagnet with the compensated antiparallel magnetic order in the ground state. Based on density-functional-theory calculations we observe that the THz-range magnon bands in have an alternating chirality splitting, similar to the alternating spin splitting of the electronic bands, and a linear magnon dispersion near the zero wave vector. We also show that, overall, the Landau damping of this metallic altermagnet is suppressed due to the spin-split electronic structure, as compared to an artificial antiferromagnetic phase of the same crystal with spin-degenerate electronic bands and chirality-degenerate magnon bands.- 20 December 2023
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 131 (25) , 256703
Top Cited PapersChiral Magnons in AltermagneticMagnons in ferromagnets have one chirality, and typically are in the GHz range and have a quadratic dispersion near the zero wave vector. In contrast, magnons in antiferromagnets are commonly considered to have bands with both chiralities that are degenerate across the entire Brillouin zone, and to be in the THz range and to have a linear dispersion near the center of the Brillouin zone. Here we theoretically demonstrate a new class of magnons on a prototypical -wave altermagnet with the compensated antiparallel magnetic order in the ground state. Based on density-functional-theory calculations we observe that the THz-range magnon bands in have an alternating chirality splitting, similar to the alternating spin splitting of the electronic bands, and a linear magnon dispersion near the zero wave vector. We also show that, overall, the Landau damping of this metallic altermagnet is suppressed due to the spin-split electronic structure, as compared to an artificial antiferromagnetic phase of the same crystal with spin-degenerate electronic bands and chirality-degenerate magnon bands. - 4 August 2023
- Published by Elsevier in Computer Physics Communications
- Vol. 292
Adaptive Anderson mixing for electronic structure calculations
- 4 August 2023
- Published by Elsevier in Computer Physics Communications
- Vol. 292
Adaptive Anderson mixing for electronic structure calculations
- 8 November 2022
- Published by Wiley in Zeitschrift für anorganische und allgemeine Chemie
- Vol. 648 (21)
Dependence of the Electronic Structure of β‐Si6−zAlzOzN8−z on the (Al,O) Concentration z and on the Temperature
β‐Si6−zAlzOzN8−z is a prominent example of systems suitable as hosts for creating materials for light‐emitting diodes (LEDs). In this work, the electronic structure of a series of semiordered and disordered β‐Si6−zAlzOzN8−z systems is investigated by means of ab initio calculations, using the FLAPW and Green function KKR methods. Finite temperature effects are included by averaging over thermodynamic configurations within the alloy analogy model. We found that the dependence of the electronic structure on the (Al,O) concentration z is similar for semiordered and disordered structures. The electronic band gap decreases with increasing z by about 1.5 eV when going from z=0 to z=2. States at the top of the valence band are mostly associated with N atoms whereas the states at the bottom of the conduction band are mostly derived from O atoms. Increasing the temperature leads to a shift of the bottom of the conduction band to lower energies. The amount of this shift increases with increasing z.
- 8 November 2022
- Published by Wiley in Zeitschrift für anorganische und allgemeine Chemie
- Vol. 648 (21)
Dependence of the Electronic Structure of β‐Si6−zAlzOzN8−z on the (Al,O) Concentration z and on the Temperature
β‐Si6−zAlzOzN8−z is a prominent example of systems suitable as hosts for creating materials for light‐emitting diodes (LEDs). In this work, the electronic structure of a series of semiordered and disordered β‐Si6−zAlzOzN8−z systems is investigated by means of ab initio calculations, using the FLAPW and Green function KKR methods. Finite temperature effects are included by averaging over thermodynamic configurations within the alloy analogy model. We found that the dependence of the electronic structure on the (Al,O) concentration z is similar for semiordered and disordered structures. The electronic band gap decreases with increasing z by about 1.5 eV when going from z=0 to z=2. States at the top of the valence band are mostly associated with N atoms whereas the states at the bottom of the conduction band are mostly derived from O atoms. Increasing the temperature leads to a shift of the bottom of the conduction band to lower energies. The amount of this shift increases with increasing z.
- Open AccessDependence of the electronic structure of $β$-Si$_{6-z}$Al$_{z}$O$_{z}$N$_{8-z}$ on the (Al,O) concentration $z$ and on the temperatureSiAlON is a prominent example of systems suitable as hosts for creating materials for light-emitting diodes (LEDs). In this work, the electronic structure of a series of semiordered and disordered SiAlON systems is investigated by means of ab initio calculations, using the FLAPW and Green function KKR methods. Finite temperature effects are included by averaging over thermodynamic configurations within the alloy analogy model. We found that the dependence of the electronic structure on the (Al,O) concentration $z$ is similar for semiordered and disordered structures. The electronic band gap decreases with increasing $z$ by about 1.5 eV when going from $z$=0 to $z$=2. States at the top of the valence band are mostly associated with N atoms whereas the states at the bottom of the conduction band are mostly derived from O~atoms. Increasing the temperature leads to a shift of the bottom of the conduction band to lower energies. The amount of this shift increases with increasing $z$.Open AccessDependence of the electronic structure of $β$-Si$_{6-z}$Al$_{z}$O$_{z}$N$_{8-z}$ on the (Al,O) concentration $z$ and on the temperatureSiAlON is a prominent example of systems suitable as hosts for creating materials for light-emitting diodes (LEDs). In this work, the electronic structure of a series of semiordered and disordered SiAlON systems is investigated by means of ab initio calculations, using the FLAPW and Green function KKR methods. Finite temperature effects are included by averaging over thermodynamic configurations within the alloy analogy model. We found that the dependence of the electronic structure on the (Al,O) concentration $z$ is similar for semiordered and disordered structures. The electronic band gap decreases with increasing $z$ by about 1.5 eV when going from $z$=0 to $z$=2. States at the top of the valence band are mostly associated with N atoms whereas the states at the bottom of the conduction band are mostly derived from O~atoms. Increasing the temperature leads to a shift of the bottom of the conduction band to lower energies. The amount of this shift increases with increasing $z$.
- 17 October 2022
- Published by American Physical Society (APS) in Physical Review B
- Vol. 106 (14) , 144416
Temperature-induced changes in the magnetism of Laves phase rare-earth-iron intermetallics by ab initio calculations
Laves compounds, where is a rare earth, exhibit technologically relevant properties associated with the interplay between their lattice geometry and magnetism. We apply ab initio calculations to explore how magnetic properties of Fe in systems vary with temperature. We found that the ratio between the orbital magnetic moment and the spin magnetic moment increases with increasing temperature for , and . This increase is significant and it should be experimentally observable by means of x-ray magnetic circular dichroism. We conjecture that the predicted increase of the ratio with temperature is linked to the reduction of hybridization between same-spin-channel states of atoms with fluctuating magnetic moments and to the associated increase of their atomic-like character.- 17 October 2022
- Published by American Physical Society (APS) in Physical Review B
- Vol. 106 (14) , 144416
Temperature-induced changes in the magnetism of Laves phase rare-earth-iron intermetallics by ab initio calculations
Laves compounds, where is a rare earth, exhibit technologically relevant properties associated with the interplay between their lattice geometry and magnetism. We apply ab initio calculations to explore how magnetic properties of Fe in systems vary with temperature. We found that the ratio between the orbital magnetic moment and the spin magnetic moment increases with increasing temperature for , and . This increase is significant and it should be experimentally observable by means of x-ray magnetic circular dichroism. We conjecture that the predicted increase of the ratio with temperature is linked to the reduction of hybridization between same-spin-channel states of atoms with fluctuating magnetic moments and to the associated increase of their atomic-like character.- Open Access
Temperature-induced changes in the magnetism of Laves phase rare-earth--iron intermetallics by ab~initio calculations
Laves RFe2 compounds, where R is a rare earth, exhibit technologically relevant properties associated with the interplay between their lattice geometry and magnetism. We apply ab~initio calculations to explore how magnetic properties of Fe in RFe2 systems vary with temperature. We found that the ratio between the orbital magnetic moment m_orb and the spin magnetic moment m_spin increases with increasing temperature for YFe2, GdFe2, TbFe2, DyFe2, and HoFe2. This increase is significant and it should be experimentally observable by means of x-ray magnetic circular dichroism. We conjecture that the predicted increase of the m_orb/m_spin ratio with temperature is linked to the reduction of hybridization between same-spin-channel states of atoms with fluctuating magnetic moments and to the associated increase of their atomic-like character.
Open AccessTemperature-induced changes in the magnetism of Laves phase rare-earth--iron intermetallics by ab~initio calculations
Laves RFe2 compounds, where R is a rare earth, exhibit technologically relevant properties associated with the interplay between their lattice geometry and magnetism. We apply ab~initio calculations to explore how magnetic properties of Fe in RFe2 systems vary with temperature. We found that the ratio between the orbital magnetic moment m_orb and the spin magnetic moment m_spin increases with increasing temperature for YFe2, GdFe2, TbFe2, DyFe2, and HoFe2. This increase is significant and it should be experimentally observable by means of x-ray magnetic circular dichroism. We conjecture that the predicted increase of the m_orb/m_spin ratio with temperature is linked to the reduction of hybridization between same-spin-channel states of atoms with fluctuating magnetic moments and to the associated increase of their atomic-like character.
- 8 October 2021
- Published by American Physical Society (APS) in Physical Review B
- Vol. 104 (14) , 144302
Effect of lattice excitations on transient near-edge x-ray absorption spectroscopy
Time-dependent and constituent-specific spectral changes in soft near-edge x-ray absorption spectroscopy (XAS) of an metal/insulator heterostructure after laser excitation are analyzed at the O K-edge with picosecond time resolution. The oxygen absorption edge of the insulator features a uniform intensity decrease of the fine structure at elevated phononic temperatures, which can be quantified by a simple simulation and fitting procedure presented here. Combining XAS with ultrafast electron diffraction measurements and ab initio calculations demonstrates that the transient intensity changes in XAS can be assigned to a transient lattice temperature. Thus, the sensitivity of transient near-edge XAS to phonons is demonstrated.- 8 October 2021
- Published by American Physical Society (APS) in Physical Review B
- Vol. 104 (14) , 144302
Effect of lattice excitations on transient near-edge x-ray absorption spectroscopy
Time-dependent and constituent-specific spectral changes in soft near-edge x-ray absorption spectroscopy (XAS) of an metal/insulator heterostructure after laser excitation are analyzed at the O K-edge with picosecond time resolution. The oxygen absorption edge of the insulator features a uniform intensity decrease of the fine structure at elevated phononic temperatures, which can be quantified by a simple simulation and fitting procedure presented here. Combining XAS with ultrafast electron diffraction measurements and ab initio calculations demonstrates that the transient intensity changes in XAS can be assigned to a transient lattice temperature. Thus, the sensitivity of transient near-edge XAS to phonons is demonstrated.- 17 May 2021
- Published by American Physical Society (APS) in Physical Review B
- Vol. 103 (17) , 174419
Spin-spiral state of a Mn monolayer on W(110) studied by soft x-ray absorption spectroscopy at variable temperature
The noncollinear magnetic state of epitaxial Mn monolayers on tungsten (110) crystal surfaces is investigated by means of soft x-ray absorption spectroscopy to complement earlier spin-polarized scanning tunneling microscopy experiments. X-ray absorption spectra (XAS), x-ray linear dichroism (XLD) and field-induced x-ray magnetic circular dichroism (XMCD) Mn -edge spectra were measured in the temperature range from 8 to 300 K and compared to results of fully relativistic ab initio calculations. We show that antiferromagnetic (AFM) helical and cycloidal spirals give rise to significantly different Mn -edge XLD signals, enabling, thus, to distinguish between them. It follows from our results that the magnetic ground state of a Mn monolayer on W(110) is an AFM cycloidal spin spiral. Based on temperature-dependent XAS, XLD, and field-induced XMCD spectra we deduce that magnetic properties of the Mn monolayer on W(110) vary with temperature, but this variation lacks a clear indication of a phase transition in the investigated temperature range up to 300 K—even though a crossover exists around 170 K in the temperature dependence of XAS branching ratios and in XLD profiles.- 17 May 2021
- Published by American Physical Society (APS) in Physical Review B
- Vol. 103 (17) , 174419
Spin-spiral state of a Mn monolayer on W(110) studied by soft x-ray absorption spectroscopy at variable temperature
The noncollinear magnetic state of epitaxial Mn monolayers on tungsten (110) crystal surfaces is investigated by means of soft x-ray absorption spectroscopy to complement earlier spin-polarized scanning tunneling microscopy experiments. X-ray absorption spectra (XAS), x-ray linear dichroism (XLD) and field-induced x-ray magnetic circular dichroism (XMCD) Mn -edge spectra were measured in the temperature range from 8 to 300 K and compared to results of fully relativistic ab initio calculations. We show that antiferromagnetic (AFM) helical and cycloidal spirals give rise to significantly different Mn -edge XLD signals, enabling, thus, to distinguish between them. It follows from our results that the magnetic ground state of a Mn monolayer on W(110) is an AFM cycloidal spin spiral. Based on temperature-dependent XAS, XLD, and field-induced XMCD spectra we deduce that magnetic properties of the Mn monolayer on W(110) vary with temperature, but this variation lacks a clear indication of a phase transition in the investigated temperature range up to 300 K—even though a crossover exists around 170 K in the temperature dependence of XAS branching ratios and in XLD profiles.- Open Access
- 11 September 2020
- Published by American Physical Society (APS) in Physical Review Research
- Vol. 2 (3) , 032067
First-principles calculations of steady-state voltage-controlled magnetism: Application to x-ray absorption spectroscopy experiments
Recent x-ray absorption experiments have demonstrated the possibility to accurately monitor the magnetism of metallic heterostructures controlled via a time-independent perturbation caused, for example, by a static electric field. Using a first-principles, nonequilibrium Green's function scheme, we show how the measured dichroic signal for the corresponding steady-state situation can be related to the underlying electronic structure and its response to the external stimulus. The suggested approach works from the infinitesimal limit of linear response to the regime of strong electric field effects, which is realized in present experimental high-sensitivity investigations.
- 11 September 2020
- Published by American Physical Society (APS) in Physical Review Research
- Vol. 2 (3) , 032067
Open AccessFirst-principles calculations of steady-state voltage-controlled magnetism: Application to x-ray absorption spectroscopy experiments
Recent x-ray absorption experiments have demonstrated the possibility to accurately monitor the magnetism of metallic heterostructures controlled via a time-independent perturbation caused, for example, by a static electric field. Using a first-principles, nonequilibrium Green's function scheme, we show how the measured dichroic signal for the corresponding steady-state situation can be related to the underlying electronic structure and its response to the external stimulus. The suggested approach works from the infinitesimal limit of linear response to the regime of strong electric field effects, which is realized in present experimental high-sensitivity investigations.