arXiv subjects

David Eilmsteiner

Publications and source records attributed to David Eilmsteiner.

5 recordsLinked to original sources

arXiv2026

Dispersion and lifetimes of magnons in non-collinear magnets from time dependent density functional theory

We investigate the spin dynamics of the non-collinear kagome triangular anti-ferromagnet Mn$_3$Rh using linear response time-dependent density functional theory. To this end, we present a novel first principles computational scheme for the evaluation of the dynamical susceptibility based on the non-collinear KKR Green's functions method and a symbolic computer algebra.This approach allows us to address the Landau decay of spin waves into non-collinear electron-hole Stoner pairs being inaccessible to adiabatic methods. Our calculations reveal three distinct Goldstone modes dispersing linearly in the long-wavelength regime giving rise to the three magnon branches and we discuss their non-trivial spatial polarizations. The spin-waves turn out to be defined in the whole Brillouin zone but their Landau damping becomes substantial away from the zone's center. Surprisingly, magnons of comparable momenta and energies can feature, depending on their chirality, considerably different attenuation, in some cases of predominantly resonant character. We trace this effect to the interplay between the magnon eigenvectors and the intrinsically spin-polarized altermagnetic band structure and the resulting spectrum of non-collinear Stoner states.

cond-mat.mtrl-sci↗

arXiv2026

Dynamical magnetic susceptibility of non-collinear magnets: A novel KKR-based ab initio scheme and its application

A novel implementation of the linear response time-dependent density functional theory addressing spin excitations in non-collinear magnets based on the Korringa-Kohn-Rostoker Green's function method is presented. Following the exposition of the formalism based on the adiabatic local spin density approximation to the exchange-correlation kernel generalized to the noncollinear case, the computational scheme is discussed in detail. The formation of the Goldstone modes in non-collinear susceptibility calculations is elaborated on formally and from the numerical convergence point of view. The scheme is deployed to study the dispersion and Landau damping of magnons in the altermagnetic non-collinear kagome antiferromagnet Mn$_{3}$Ir. The non-monotonous dependence of the damping on the magnon frequency makes the large momentum excitations attractive in the terahertz spintronics. To this end, we analyze the real-time and real-space dynamics of the magnetic modes, including their strongly chirality-dependent attenuation.

cond-mat.mtrl-sci↗

arXiv2025

High temperature Neel skyrmions in simple ferromagnets

A wide variety of chiral non-collinear spin textures have been discovered and have unique properties that make them highly interesting for technological applications. However, many of these are found in complex materials and only in a narrow window of temperature. Here, we show the formation of Neel-type skyrmions in thin layers of simple ferromagnetic alloys, namely Co-Al and Co-Ni-Al, over a wide range of temperature up to 770 K, by imposing a vertical strain gradient via epitaxy with an Ir-Al underlayer. The Neel skyrmions are directly observed using Lorentz transmission electron microscopy in freestanding membranes at high temperatures and the strain gradient is directly measured from x-ray diffraction anomalous peak profiles. Our concept allows simple centrosymmetric ferromagnets with high magnetic ordering temperatures to exhibit hot skyrmions, thereby, bringing closer skyrmionic electronics.

cond-mat.mtrl-sci↗

arXiv2021

Eigenmodes of a disordered FeCo magnonic crystal at finite temperatures

In this report we present a systematic study of the magnonic modes in the disordered Fe$_{0.5}$Co$_{0.5}$ alloy based on the Heisenberg Hamiltonian using two complementary approaches. In order to account for substitutional disorder, on the one hand we directly average the transverse magnetic susceptibility in real space over different disorder configurations and on the other hand we use the coherent potential approximation (CPA). While the method of direct averaging is numerically exact, it is computationally expensive and limited by the maximal size of the supercell which can be simulated on a computer. On the contrary the CPA does not suffer from this drawback and yields a cheap numerical scheme. Therefore, we additionally compare the results of these two approaches and show that the CPA gives very good results for most of the magnetic properties, including the magnon energies and the spatial shape of the eigenmodes. However, it turns out that while reproducing the general trend, the CPA systematically underestimates the disorder induced damping of the magnons. This provides evidence that the physics of impurity scattering in this system is governed by non-local effects missing in the CPA. Finally, we study the real space eigenmodes of the system, including their spatial shapes, and analyze their temperature dependence within the random phase approximation.

cond-mat.dis-nn↗

arXiv2021

Spin waves in alloys at finite temperatures: application for FeCo magnonic crystal

We study theoretically the influence of the temperature and disorder on the spin wave spectrum of the magnonic crystal Fe$_{1-c}$Co$_{c}$. Our formalism is based on the analysis of a Heisenberg Hamiltonian by means of the wave vector and frequency dependent transverse magnetic susceptibility. The exchange integrals entering the model are obtained from the \emph{ab initio} magnetic force theorem. The coherent potential approximation is employed to treat the disorder and random phase approximation in order to account for the softening of the magnon spectrum at finite temperatures. The alloy turns out to exhibit many advantageous properties for spintronic applications. Apart from high Curie temperature, its magnonic bandgap remains stable at elevated temperatures and is largely unaffected by the disorder. We pay particular attention to the attenuation of magnons introduced by the alloying. The damping turns out to be a non-monotonic function of the impurity concentration due to the non-trivial evolution of the value of exchange integrals with the Co concentration. The disorder induced damping of magnons is estimated to be much smaller than their Landau damping.

cond-mat.mtrl-sci↗