| 1. |
- Cardias, Ramon, et al.
(author)
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Comment on "Proper and improper chiral magnetic interactions"
- 2022
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In: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 105:2
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Journal article (peer-reviewed)abstract
- In a recent paper by dos Santos Dias et al. [Phys. Rev. B 103, L140408 (2021)], a critique of earlier works analyzing low-energy spin Hamiltonians is put forth. To be precise, it is the large noncollinear contributions to the Dzyaloshinskii-Moriya interaction (DMI) that is the main concern of dos Santos Dias et al. In this Comment, we clarify the microscopic mechanisms for the large DMI that can be found in noncollinear magnets. Furthermore, we outline the complementary nature of the different parametrizations of a spin Hamiltonian, with strengths and weaknesses of both approaches. Specifically, we stress the physical insight in the interpretation of the DMI, when decomposed in microscopic electron and spin densities and currents.
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| 2. |
- Cardias, Ramon, et al.
(author)
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Coupled spin-lattice dynamics from the tight-binding electronic structure
- 2024
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 109:14
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Journal article (peer-reviewed)abstract
- We developed a method which performs the coupled adiabatic spin and lattice dynamics based on the tight-binding electronic structure model, where the intrinsic magnetic field and ionic forces are calculated from the converged self-consistent electronic structure at every time step. By doing so, this method allows us to explore limits where the physics described by a parameterized spin-lattice Hamiltonian is no longer accurate. We demonstrate how the lattice dynamics is strongly influenced by the underlying magnetic configuration, where disorder is able to induce significant lattice distortions. The presented method requires significantly less computational resources than ab initio methods, such as time-dependent density functional theory (TD-DFT). Compared to parameterized Hamiltonian-based methods, it also describes more accurately the dynamics of the coupled spin and lattice degrees of freedom, which becomes important outside of the regime of small lattice and spin fluctuations.
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| 3. |
- Liu, Yuefei, et al.
(author)
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Tunable phonon-driven magnon-magnon entanglement at room temperature
- 2023
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In: New Journal of Physics. - : IOP Publishing Ltd. - 1367-2630. ; 25:11
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Journal article (peer-reviewed)abstract
- We report the existence of entangled steady-states in bipartite quantum magnonic systems at elevated temperatures. We consider dissipative dynamics of two magnon modes in a bipartite antiferromagnet, subjected to interaction with a phonon mode and an external rotating magnetic field. To quantify the bipartite magnon-magnon entanglement, we use entanglement negativity and compute its dependence on temperature and magnetic field. We provide evidence that the coupling between magnon and phonon modes is necessary for the entanglement, and that, for any given phonon frequency and magnon-phonon coupling rate, there are always ranges of the magnetic field amplitudes and frequencies for which magnon-magnon entanglement persists at room temperature.
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| 4. |
- Lu, Zhiwei, et al.
(author)
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Influence of nonlocal damping on magnon properties of ferromagnets
- 2023
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 108:1
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Journal article (peer-reviewed)abstract
- We study the influence of nonlocal damping on the magnon properties of Fe, Co, Ni, and Fe1-xCox (x=30%,50%) alloys. The Gilbert damping parameter is typically considered as a local scalar both in experiment and in theoretical modeling. However, recent works have revealed that Gilbert damping is a nonlocal quantity that allows for energy dissipation between atomic sites. With the Gilbert damping parameters calculated from a state-of-the-art real-space electronic structure method, magnon lifetimes are evaluated from spin dynamics and linear response, where a good agreement is found between these two methods. It is found that nonlocal damping affects the magnon lifetimes in different ways depending on the system. Specifically, we find that in Fe, Co, and Ni, the nonlocal damping decreases the magnon lifetimes, while in Fe70Co30 and Fe50Co50 an opposite, nonlocal damping effect is observed, and our data show that it is much stronger in the former.
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| 5. |
- Sato, Takuma, et al.
(author)
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Dynamic magnetoelastic boundary conditions and the pumping of phonons
- 2021
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:1
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Journal article (peer-reviewed)abstract
- We derive boundary conditions at the interfaces of magnetoelastic heterostructures under ferromagnetic resonance for arbitrary magnetization directions and interface shapes. We apply our formalism to magnet' nonmagnet bilayers and magnetic grains embedded in a nonmagnetic thin film, revealing a nontrivial magnetization angle dependence of acoustic phonon pumping.
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| 6. |
- Streib, Simon, et al.
(author)
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Adiabatic spin dynamics and effective exchange interactions from constrained tight-binding electronic structure theory : Beyond the Heisenberg regime
- 2022
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In: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 105:22
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Journal article (peer-reviewed)abstract
- We consider an implementation of the adiabatic spin dynamics approach in a tight-binding description of the electronic structure. The adiabatic approximation for spin degrees of freedom assumes that the faster electronic degrees of freedom are always in a quasiequilibrium state, which significantly reduces the numerical complexity in comparison to the full electron dynamics. Noncollinear magnetic configurations are stabilized by a constraining field, which allows us to directly obtain the effective magnetic field from the negative of the constraining field. While the dynamics are shown to conserve energy, we demonstrate that adiabatic spin dynamics does not conserve the total spin angular momentum when the lengths of the magnetic moments are allowed to change, which is confirmed by numerical simulations. Furthermore, we develop a method to extract an effective two-spin exchange interaction from the energy curvature tensor of noncollinear states, which we calculate at each time step of the numerical simulations. We demonstrate the effect of noncollinearity on this effective exchange and limitations due to multispin interactions in strongly noncollinear configurations beyond the regime where the Heisenberg model is valid. The relevance of the results are discussed with respect to experimental pump-probe experiments that follow the ultrafast dynamics of magnetism.
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| 7. |
- Streib, Simon
(author)
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Difference between angular momentum and pseudoangular momentum
- 2021
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:10
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Journal article (peer-reviewed)abstract
- In condensed matter systems it is necessary to distinguish between the momentum of the constituents of the system and the pseudomomentum of quasiparticles. The same distinction is also valid for angular momentum and pseudoangular momentum. Based on Noether's theorem, we demonstrate that the recently discussed orbital angular momenta of phonons and magnons are pseudoangular momenta. This conceptual difference is important for a proper understanding of the transfer of angular momentum in condensed matter systems, especially in spintronics applications.
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| 8. |
- Streib, Simon, et al.
(author)
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Equation of motion and the constraining field in ab initio spin dynamics
- 2020
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 102:21
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Journal article (peer-reviewed)abstract
- It is generally accepted that the effective magnetic field acting on a magnetic moment is given by the gradient of the energy with respect to the magnetization. However, in ab initio spin dynamics within the adiabatic approximation, the effective field is also known to be exactly the negative of the constraining field, which acts as a Lagrange multiplier to stabilize an out-of-equilibrium, noncollinear magnetic configuration. We show that for Hamiltonians without mean-field parameters both of these fields are exactly equivalent, while there can be a finite difference for mean-field Hamiltonians. For density functional theory (DFT) calculations, the constraining field obtained from the auxiliary Kohn-Sham Hamiltonian is not exactly equivalent to the DFT energy gradient. This inequality is highly relevant for both ab initio spin dynamics and the ab initio calculation of exchange constants and effective magnetic Hamiltonians. We argue that the effective magnetic field and exchange constants have the highest accuracy in DFT when calculated from the energy gradient and not from the constraining field.
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| 9. |
- Streib, Simon, et al.
(author)
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Exchange constants for local spin Hamiltonians from tight-binding models
- 2021
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:22
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Journal article (peer-reviewed)abstract
- We consider the mapping of tight-binding electronic structure theory to a local spin Hamiltonian, based on the adiabatic approximation for spin degrees of freedom in itinerant-electron systems. Local spin Hamiltonians are introduced in order to describe the energy landscape of small magnetic fluctuations, locally around a given spin configuration. They are designed for the linear response near a given magnetic state and, in general, are insufficient to capture arbitrarily strong deviations of spin configurations from the equilibrium. In order to achieve this mapping, we include a linear term in the local spin Hamiltonian that together with the usual bilinear exchange tensor, produces an improved accuracy of effective magnetic Weiss fields for noncollinear states. We also provide examples from tight-binding electronic structure theory, where our implementation of the calculation of exchange constants is based on constraining fields that stabilize an out-of-equilibrium spin configuration. We check our formalism by means of numerical calculations for iron dimers and chains.
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