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Stabilization of unusual spin-orbit-driven magnetic orderings are achieved for chains of Mn atoms deposited on a W(110) substrate. First-principles electronic structure calculations show that the ground-state spin configuration is noncollinear, forming chiral spiral-like structures, driven by competing nearest-and next-nearest-neighbor interactions. The orbital magnetic moments are also found to exhibit noncollinear ordering that, interestingly, tend to align in-plane for some systems with an orientation distinctly differently from that of the spin moment. We analyze the mechanism behind such behavior, and find that it is due to the competition between the spin-orbit interaction and crystal-field splitting. Model calculations based on this assumption reproduce the main findings observed in our first-principles calculations.

Despite extensive research on magnetic skyrmions and antiskyrmions, a significant challenge remains in crafting nontrivial high-order skyrmionic textures with varying, or even tailor-made, topologies. We address this challenge, by focusing on a construction pathway of skyrmionic metamaterials within a monolayer thin film and suggest several skyrmionic metamaterials that are surprisingly stable, i.e., long-lived, due to a self-stabilization mechanism. This makes these new textures promising for applications. Central to our approach is the concept of 'simulated controlled assembly', in short, a protocol inspired by 'click chemistry' that allows for positioning topological magnetic structures where one likes, and then allowing for energy minimization to elucidate the stability. Utilizing high-throughput atomistic-spin-dynamic simulations alongside state-of-the-art AI-driven tools, we have isolated skyrmions (topological charge Q = 1), antiskyrmions (Q = - 1), and skyrmionium (Q = 0). These entities serve as foundational 'skyrmionic building blocks' to form the here-reported intricate textures. In this work, two key contributions are introduced to the field of skyrmionic systems. First, we present a novel combination of atomistic spin dynamics simulations and controlled assembly protocols for the stabilization and investigation of new topological magnets. Second, using the aforementioned methods we report on the discovery of skyrmionic metamaterials.

Among the quasi-two-dimensional van der Waals magnetic systems, Fe4GeTe2 makes a profound impact due to its near-room-temperature ferromagnetic behavior and the complex magnetothermal phase diagram exhibiting multiple phase transformations, as observed from magnetization and magnetotransport measurements. A complete analysis of these phase transformations in light of electronic correlation and its impact on the underlying magnetic interactions remain unexplored in the existing literature. Using first-principles methodologies, incorporating the dynamical nature of electron correlation, we have analyzed the interplay of the direction of magnetization in an easy-plane and easy-axis manner with the underlying crystal symmetry, which reveals the opening of a pseudogap feature beyond the spin-reorientation transition temperature. The impact of dynamical correlation on the calculated magnetic circular dichroism and x-ray absorption spectrum of the L-edge of Fe atoms compare well with existing experimental observations. The calculated intersite Heisenberg exchange interactions display a complicated nature, depending upon the pairwise interactions among the two inequivalent Fe sites, indicating a Ruderman-Kittel-Kasuya-Yosida-like behavior of the magnetic interactions. We note the existence of significant anisotropic and antisymmetric exchange interactions, resulting in a chirality in the magnetic behavior of the system. Subsequent investigation of the dynamical aspects of magnetism in Fe4GeTe2 and the respective magnetothermal phase diagram reveals that the dynamical nature of spins and the decoupling of the magnetic properties for both sites of Fe is crucial to explain all the experimentally observed phase transformations.

Fe₃GeTe₂ and Fe₃GaTe₂ are ferromagnetic conducting materials of van der Waals type with unique magnetic properties that are highly promising for the development of new spintronic, orbitronic, and magnonic devices. Even in the form of two-dimensional-like ultrathin films, they exhibit a relatively high Curie temperature, magnetic anisotropy perpendicular to the atomic planes, and multiple types of Hall effects. We explore nanoribbons made from single layers of these materials and show that they display noncollinear magnetic ordering at their edges. This magnetic inhomogeneity allows angular momentum currents to generate magnetic torques at the sample edges, regardless of their polarization direction, significantly enhancing the effectiveness of magnetization manipulation in these systems. We also demonstrate that it is possible to rapidly reverse the magnetization direction of these nanostructures by means of spin–orbit and spin-transfer torques with rather low current densities, making them quite propitious for nonvolatile magnetic memory units.

To develop new devices based on synthetic ferrimagnetic heterostructures, understanding the material's physical properties is pivotal. Here, the induced magnetic moment (IMM), magnetic exchange coupling, and spin textures are investigated in Pt(1 nm)/Co(1.5 nm)/Gd(1 nm) multilayers using a multiscale approach. The magnitude and direction of the IMM are interpreted in the framework of both X-ray magnetic circular dichroism and density functional theory. The IMM transferred by Co across the Gd paramagnetic thickness leads to a nontrivial flipped spin state (FSS) within the Gd layers, in which their magnetic moments couple antiparallel/parallel with the ferromagnetic Co near/far from the Co/Gd interface, respectively. The FSS depends on the magnetic field, which, on average, reduces the Gd magnetic moment as the field increases. For the Pt, in both Pt/Co and Gd/Pt interfaces, the IMM follows the same direction as the Co magnetic moment, with negligible IMM in the Gd/Pt interface. Additionally, zero-field spin spirals were imaged using scanning transmission X-ray microscopy, whereas micromagnetic simulations were employed to unfold the interactions, stabilizing the ferrimagnetic configurations, where the existence of a sizable Dzyaloshinskii-Moriya interaction is demonstrated to be crucial.

PdFe/Ir(111) has attracted tremendous attention for next-generation spintronics devices due to existence of magnetic skyrmions with the external magnetic field. Our density functional theoretical calculations in combination with spin dynamics simulation suggest that the spin spiral phase in fcc stacked PdFe/Ir(111) flips into the skyrmion lattice phase around B-ert similar to 6 T. This leads to the microscopic understanding of the thermodynamic and kinetic behaviours affected by the intrinsic spin-lattice couplings (SLCs) in this skyrmion material for magneto-mechanical properties. Here we calculate fully relativistic SLC parameters from first principle computations and investigate the effect of SLC on dynamical magnetic interactions in skyrmion multilayers PdFe/Ir(111). The exchange interactions arising from next nearest-neighbors (NN) in this material are highly frustrated and responsible for enhancing skyrmion stability. We report the larger spin-lattice effect on both dynamical Heisenberg exchanges and Dzyaloshinskii-Moriya interactions for next NN compared to NN which is in contrast with recently observed spin-lattice effect in bulk bcc Fe and CrI3 monolayer. Based on our analysis, we find that the effective measures of SLCs in fcc (hcp) stacking of PdFe/Ir(111) are similar to 2.71(similar to 2.36) and similar to 14.71(similar to 21.89) times stronger for NN and next NN respectively, compared to bcc Fe. The linear regime of displacement for SLC parameters is <= 0.02 angstrom which is 0.72% of the lattice constant for PdFe/Ir(111). The microscopic understanding of SLCs provided by our current study could help in designing spintronic devices based on thermodynamic properties of skyrmion multilayers.

Magnetoelasticity plays a crucial role in numerous magnetic phenomena, including magnetocalorics, magnon excitation via acoustic waves, and ultrafast demagnetization, or the Einstein-de Haas effect. Despite a long-standing discussion on anisotropy-mediated magnetoelastic interactions of relativistic origin, the exchangemediated magnetoelastic parameters within an atomistic framework have only recently begun to be investigated. As a result, many of their behaviors and values for real materials remain poorly understood. Therefore, by using a proposed simple modification of the embedded cluster approach that reduces the computational complexity, we critically analyze the properties of exchange-mediated spin-lattice coupling parameters for elemental 3d ferromagnets (bcc Fe, fcc Ni, and fcc Co), comparing methods used for their extraction and relating their realistic values to symmetry considerations and orbitally decomposed contributions. Additionally, we investigate the effects of noncollinearity (spin temperature) and applied pressure on these parameters. For Fe, we find that singlesite rotations, associated with spin temperatures around 100 K, induce significant modifications, particularly in Dzyaloshinskii-Moriya-type couplings; in contrast, such interactions in Co and Ni remain almost configuration independent. Moreover, we demonstrate a notable change in the exchange-mediated magnetoelastic constants for Fe under isotropic contraction. Finally, the conversion between atomistic, quantum-mechanically derived parameters and the phenomenological magnetoelastic theory is discussed, which can be a useful tool towards larger and more realistic dynamics simulations involving coupled subsystems.

Femtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. Several microscopic mechanisms have been proposed to explain these observations, including the transport of ultrashort spin-polarized hot-electrons (SPHE). However, currently such ultrafast spin currents are only poorly characterized due to the measurement requirements for element and time resolution. Here, using time- and element-resolved X-ray magnetic circular dichroism alongside atomistic spin-dynamics simulations, we study the ultrafast transfer of the angular momentum from spin-polarized currents. We show that using a Co/Pt multilayer as a polarizer in a spin-valve structure, the SPHE drives the demagnetization of the two sub-lattices of the Fe₇₄Gd₂₆ film. This behaviour can be explained with two physical mechanisms; spin transfer torque and thermal fluctuations induced by the SPHE. We provide a quantitative description of the heat transfer of the ultrashort SPHE pulse to the Fe₇₄Gd₂₆ films, as well as the effect of spin-polarization of the SPHE current density responsible for the observed magnetization dynamics. Our work finally characterizes the spin-polarization of the SPHEs revealing unexpected opposite spin polarization to the Co magnetization.

We study the ultrafast demagnetization dynamics of 𝐿⁢𝑛⁢Rh₂⁢Si₂(𝐿⁢𝑛=Pr, Nd, Sm, Gd, Tb, Dy, Ho) antiferromagnets after excitation by a laser pulse, using a combination of density functional theory and atomistic spin and spin-lattice dynamics simulations. In the first step, we calculate the Heisenberg interactions using the magnetic force theorem and compare two approaches, where the 4⁢𝑓 states of the rare earths are treated as frozen core states or as valence states with added correlation corrections. We find marked quantitative differences in terms of predicted Curie temperature for most of the systems, especially for those with a large orbital moment of the rare-earth cations. This can be attributed to the importance of indirect interactions of the 4⁢𝑓 states through the Si states, which depends on the binding energy of the 4⁢𝑓 states and coexists with Ruderman-Kittel-Kasuya-Yosida–type interactions mediated by the conduction states. However, qualitatively both approaches agree in terms of the predicted antiferromagnetic ordering at low temperature, which is in line with previous experiments. In the second step, the atomistic dynamics simulations are used in combination with a heat-conserving two-temperature model, which allows for the calculation of spin and electronic temperatures during the magnetization dynamics simulations. Our simulations demonstrate that despite quite different demagnetization times, magnetization dynamics of all studied 𝐿⁢𝑛⁢Rh₂⁢Si₂ antiferromagnets exhibit similar two-step behavior, in particular the first fast drop followed by slower demagnetization. In addition, we observe that the demagnetization amplitude depends linearly on laser fluence, for low fluences, something that is also in agreement with experimental observations. We also investigate the impact of lattice dynamics on ultrafast demagnetization using coupled atomistic spin-lattice dynamics simulations and the heat-conserving three-temperature model, which confirm the linear dependence of magnetization on laser fluence. The microscopic mechanisms behind these behaviors are investigated in detail.

The impact of the local chemical environment on the Gilbert damping in the binary alloy Fe100-xCox is investigated, using computations based on density functional theory. By varying the alloy composition x as well as Fe-Co atom positions we reveal that the effective damping of the alloy is highly sensitive to the nearest-neighbor environment, especially to the amount of Co and the average distance between Co-Co atoms at nearest-neighbor sites. Both lead to a significant local increase (up to an order of magnitude) of the effective Gilbert damping, originating mainly from variations of the density of states at the Fermi energy. In a global perspective (i.e., making a configuration average for a real material), those differences in damping are masked by statistical averages. When low-temperature explicit atomistic dynamics simulations are performed, the impact of short-range disorder on local dynamics is observed to also alter the overall relaxation rate. Our results illustrate the possibility of local chemical engineering of the Gilbert damping, which may stimulate the study of new ways to tune and control materials aiming for spintronics applications.