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Despite decades of research, the role of the lattice and its coupling to the magnetisation during ultrafast demagnetisation processes is still not fully understood. Here we report on studies of both explicit and implicit lattice effects on laser induced ultrafast demagnetisation of bcc Fe and fcc Co. We do this using atomistic spin- and lattice dynamics simulations following a heat-conserving three-temperature model. We show that this type of Langevin-based simulation is able to reproduce observed trends of the ultrafast magnetization dynamics of fcc Co and bcc Fe. The parameters used in our models are all obtained from electronic structure theory, with the exception of the lattice dynamics damping term, where a range of parameters were investigated. It was found that while the explicit spin-lattice coupling in the studied systems does not impact the demagnetisation process notably, the lattice damping has a large influence on the details of the magnetization dynamics. The dynamics of Fe and Co following the absorption of a femtosecond laser pulse are compared with previous results for Ni and similarities and differences in the materials' behavior are analysed. For all elements investigated so far with this model, we obtain a linear relationship between the value of the maximally demagnetized state and the fluence of the laser pulse , which is in agreement with experiments. Moreover, we demonstrate that the demagnetization amplitude is largest for Ni and smallest for Co. This holds over a wide range of the reported electron-phonon couplings, and this demagnetization trend is in agreement with recent experiments.

Perturbed angular correlation spectroscopy combined with ab initio electronic structure calculations is used to unravel the structural phase transition path from the low -temperature polar structure to the high -temperature structural phase in Ca 3 Ti 2 O 7 , a hybrid improper ferroelectric. The experimental procedure, conducted at ISOLDE, explores the unique features of a local probe environment approach by monitoring the evolution of the electric field gradient tensor at the calcium sites. The local environments, observed above 1057 K, confirm a structural phase transition from the A 2 1 am symmetry to an orthorhombic Acaa symmetry in the Ca 3 Ti 2 O 7 crystal lattice, disagreeing with the frequently reported avalanche structural transition from the polar A 2 1 am phase to the aristotype I 4 / mmm phase. Moreover, the EFG temperature dependency, within the A 2 1 am temperature stability, is shown to be sensitive to the recently proposed Ca 3 Ti 2 O 7 ferroelectric polarization decrease within the 500-800 K temperature range.

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.

We present a metaheuristic conditional neural-network-based method aimed at identifying physically interesting metastable states in a potential energy surface of high rugosity. To demonstrate how this method works, we identify and analyze spin textures with topological charge Q ranging from 1 to −13 (where antiskyrmions have Q <0) in the Pd/Fe/Ir(111) system, which we model using a classical atomistic spin Hamiltonian based on parameters computed from density functional theory. To facilitate the harvest of relevant spin textures, we make use of the newly developed segment anything model. Spin textures with Q ranging from −3 to −6 are further analyzed using finite-temperature spin-dynamics simulations. We observe that for temperatures up to around 20 K, lifetimes longer than 200 ps are predicted, and that when these textures decay, new topological spin textures are formed. We also find that the relative stability of the spin textures depend linearly on the topological charge, but only when comparing the most stable antiskyrmions for each topological charge. In general, the number of holes (i.e., non-self-intersecting curves that define closed domain walls in the structure) in the spin texture is an important predictor of stability—the more holes, the less stable the texture. Methods for systematic identification and characterization of complex metastable skyrmionic textures—such as the one demonstrated here—are highly relevant for advancements in the field of topological spintronics.

Magnetic skyrmions are prime candidates for the nextgenerationof spintronic devices. Skyrmions and other topological magnetic structuresare known to be stabilized by the Dzyaloshinskii-Moriya interaction(DMI) that occurs when the inversion symmetry is broken in thin films.Here, we show by first-principles calculations and atomistic spindynamics simulations that metastable skyrmionic states can also befound in nominally symmetric multilayered systems. We demonstratethat this is correlated with the large enhancement of the DMI strengthdue to the presence of local defects. In particular, we find thatmetastable skyrmions can occur in Pd/Co/Pd multilayers without externalmagnetic fields and can be stable even near room temperature conditions.Our theoretical findings corroborate with magnetic force microscopyimages and X-ray magnetic circular dichroism measurements and highlightthe possibility of tuning the intensity of DMI by using interdiffusionat thin film interfaces.

Structurally similar transition metal systems can have widely differing magnetic properties. A prime example of this is found for bilayers on Ir(111), where the Pd/Fe/Ir(111) ground state has a well-established noncollinear spin texture, while Pd/Co/Ir(111) presents a ferromagnetic (FM) single domain. To unravel the origins of these different magnetic behaviors, an investigation of Pd/Fe and Pd/Co bilayers on Ir(111) is here performed. Based on the obtained ab initio electronic structure, exchange coupling parameters Ji j,and Dzyaloshinskii-Moriya interactions (DMIs), we demonstrate that, although in Pd/Co/Ir(111) the DMI is significant, two ingredients play a key role in the origin of noncollinearity in Pd/Fe/Ir(111): the presence of magnetic frustrations and a much more in-plane DMI, both with a long-range influence. The Jij and DMI behaviors in both systems can be explained in terms of a simple rigid-band-like model. Also, by performing spin-dynamics simulations with the magnetic parameters tuned from the Pd/Co/Ir(111) to Pd/Fe/Ir(111) ab initio values, we could find conditions for the emergence of skyrmionic phases in the originally FM Pd/Co/Ir(111).

Multireservoir models are widely used for modeling and interpreting ultrafast magnetization dynamics. Here we introduce an alternative formulation to existing three-temperature models for the treatment of spin, electron, and lattice temperatures in magnetization dynamics simulations. In contrast to most existing models of calculations of energy transfer between reservoirs in these types of simulations, the heat distribution of the spin and lattice subsystems is evaluated during the simulation instead of being calculated a priori. The model is applied to investigate the demagnetization and remagnetization of fcc Ni, when subjected to a strong laser pulse. In particular, our model results in a fast interplay between the electron and spin subsystems which reproduces the main features of experimental data for fcc Ni significantly better than most reported three-temperature models. We also show that the way in which the electron, spin, and lattice heat capacities are described can have a significant impact on the simulated ultrafast dynamics. By introducing spin-lattice couplings in the simulation, it is shown that these explicit interactions only have a marginal impact on the magnetization dynamics of fcc Ni, albeit it is more pronounced for higher laser pulse powers.

[ES] El monográfico está formado por una recopilación de artículos que fueron presentados, a modo de comunicaciones, en el II Congreso Interdisciplinar de Jóvenes Historiadores impulsado por la Asociación de Jóvenes Historiadores (AJHIS), con la colaboración de la Asociación de Jóvenes Investigadores de Teoría e Historia de la Educación (AJITHE), y que se celebró en la Universidad de Salamanca durante los días 24, 25, 26 y 27 de mayo de 2011.

The Landau-Lifshitz-Gilbert (LLG) and Landau-Lifshitz (LL) equations play an essential role for describing the dynamics of magnetization in solids. While a quantum analog of the LL dynamics has been proposed in [Phys. Rev. Lett. 110, 147201 (2013)], the corresponding quantum version of LLG remains unknown. Here, we propose such a quantum LLG equation that inherently conserves purity of the quantum state. We examine the quantum LLG dynamics of a dimer consisting of two interacting spin-1/2 particles. Our analysis reveals that, in the case of ferromagnetic coupling, the evolution of initially uncorrelated spins mirrors the classical LLG dynamics. However, in the antiferromagnetic scenario, we observe pronounced deviations from classical behavior, underscoring the unique dynamics of becoming a spinless state, which is non-locally correlated. Moreover, when considering spins that are initially correlated, our study uncovers an unusual form of transient quantum correlation dynamics, which differ significantly from what is typically seen in open quantum systems., QC 20240522