arXiv subjects

Hendrik Schrautzer

Publications and source records attributed to Hendrik Schrautzer.

10 recordsLinked to original sources

arXiv2026

Lifetime of bimerons and antibimerons in two-dimensional magnets

Soliton-based computing architectures have recently emerged as a promising avenue to overcome fundamental limitations of conventional information technologies, the von Neumann bottleneck. In this context, magnetic skyrmions have been widely considered for in-situ processing devices due to their mobility and enhanced lifetime in materials with broken inversion symmetry. However, modern applications in non-volatile reservoir or neuromorphic computing raise the additional demand for non-linear inter-soliton interactions. Here, we report that solitons in easy-plane magnets, such as bimerons and antibimerons, show greater versatility and potential for non-linear interactions than skyrmions and antiskyrmions, making them superior candidates for this class of applications. Using first-principles and transition state theory, we predict the coexistence of degenerate bimerons and antibimerons at zero field in a van der Waals heterostructure Fe$_3$GeTe$_2$/Cr$_2$Ge$_2$Te$_6$ -- an experimentally feasible system. We demonstrate that, owing to their distinct structural symmetry, bimerons exhibit fundamentally different behavior from skyrmions and cannot be regarded as their in-plane counterparts, as is often assumed. This distinction leads to unique properties of bimerons and antibimerons, which arise from the unbroken rotational symmetry in easy-plane magnets. These range from anisotropic soliton-soliton interactions to strong entropic effects on their lifetime, driven by the non-local nature of thermal excitations. Our findings reveal a broader richness of solitons in easy-plane magnets and underline their unique potential for spintronic devices.

cond-mat.mes-hall↗

arXiv2026

Emergence of multiple topological spin textures in an all-magnetic van der Waals heterostructure

Magnetic solitons such as skyrmions and bimerons show great promise for both fundamental research and spintronic applications. Stabilizing and controlling topological spin textures in atomically thin van der Waals (vdW) materials has gained tremendous attention due to high tunability, enhanced functionality, and miniaturization. Here, we present an efficient spin-spiral approach based on first-principles, a method for mapping magnetic interactions from collective models onto arbitrary lattice symmetries, such as hexagonal and honeycomb lattices. Using atomistic spin models parametrized from first-principles, we predict the emergence of multiple topological spin textures in an all-magnetic vdW heterostructure Fe$_3$GeTe$_2$/Cr$_2$Ge$_2$Te$_6$ (FGT/CGT) -- an experimentally feasible system. Interestingly, the FGT layer favors out-of-plane magnetization, whereas the CGT layer prefers in-plane magnetocrystalline anisotropy. Néel-type nanoscale skyrmions are formed at zero field in the FGT layer due to interfacial Dzyaloshinskii-Moriya interaction (DMI), while nanoscale bimerons and antibimerons can co-exist in the CGT layer by the interplay between exchange frustration and DMI. Using the collective approach we apply, we reveal significant discretization effects in hexagonal and honeycomb geometries. In particular, we demonstrate that the lifting of geometric exchange frustration on the honeycomb significantly affects soliton barriers and pinning energetics. These fundamental results not only highlight the importance of spin simulations in discrete models for topological magnetism, especially in 2D materials, but may also help to pave the way for solitonic devices based on atomically thin vdW heterostructures.

cond-mat.mtrl-sci↗

arXiv2026

Skyrmions in 2D chiral magnets with noncollinear ground states stabilized by higher-order interactions

Magnetic skyrmions are intriguing topological spin textures that have attracted great attention due to their potential for future spintronic devices. Skyrmions have so far been explored in different magnetic materials, such as ferromagnets, antiferromagnets, and ferrimagnets. Here, we propose a new type of unconventional skyrmions stabilized in noncollinear magnets. Using first-principles calculations and atomistic spin simulations, we demonstrate that a noncollinear ground state can be stabilized in Rh/Co and Pd/Co atomic bilayers on the Re(0001) surface by four spin exchange interactions, although Co -- a material often used in applications -- is a prototypical ferromagnet with strong pairwise exchange interaction. We further show that unconventional skyrmion lattices and isolated skyrmions can emerge on this noncollinear magnetic background. Transition-state theory calculations reveal that these metastable skyrmions are protected by large energy barriers, suggesting that they could be observed in experiments. These unconventional types of skyrmions in noncollinear magnets might open new possibilities for topological spin transport or magnet-superconductor hybrid systems.

cond-mat.mtrl-sci↗

arXiv2025

Network of localized magnetic textures revealed using a saddle-point search framework

A computational framework is presented for the sampling of the energy surface of magnetic systems via the systematic identification of first-order saddle points that determine connectivity of metastable states and define the mechanisms of transitions between them. The framework combines four stages: first, the symmetry of a given minimum-energy configuration is identified and used to define subsystems whose eigenmodes provide relevant deformation directions; the subsystem eigenmodes are then used to guide the system toward the vicinity of different saddle points surrounding the energy minimum; next, the geodesic minimum mode following method is employed to efficiently converge onto the saddle points; and finally, the identified saddle points are embedded into the state network. Applied to metastable textures in two-dimensional chiral magnets described by a lattice Hamiltonian, the method reveals a hierarchy of transition mechanisms governing the nucleation, annihilation, and rearrangement of the fundamental components of localized magnetic textures. The identified saddle points enable the construction of the network of metastable states, where saddle points define the connectivity between them, providing a comprehensive map of accessible transitions and their associated energy barriers. Transitions corresponding to both homotopies that preserve the topological charge and transformations that change it are identified. By scaling the interaction parameters, the distinct behavior of these two classes is obtained as the continuum limit is approached. Finally, it is shown that textures with the same topological charge are not always connected by a homotopy corresponding to a minimum-energy path: in specific parameter regimes, the total topological charge necessarily increases and then decreases (or vice versa) during the transition, returning to its initial value at the final state.

cond-mat.mtrl-sci↗

arXiv2025

Impact of higher-order exchange on the lifetime of skyrmions and antiskyrmions

Reliable control of skyrmion lifetime is essential for realizing spintronic devices, yet the role of higher-order exchange - which can lead to skyrmion stabilization - remains largely unexplored. Here we calculate lifetimes of isolated skyrmions and antiskyrmions at transition-metal interfaces based on an atomistic spin model that includes all fourth-order exchange terms. Within harmonic transition-state theory, we evaluate both energetic and entropic contributions and find substantially enhanced lifetimes when higher-order exchange is included. The four-spin four-site interaction raises the energy barrier and lowers the curvature of the energy landscape at the collapse saddle point, increasing the pre-exponential factor. We show that skyrmions and antiskyrmions can remain thermally stable even without Dzyaloshinskii-Moriya interaction (DMI), and that tuning the four-spin term by a small amount modulates the prefactor over orders of magnitude. Our results identify higher-order exchange as a promising route to stabilize topological magnetic textures - in particular in systems lacking DMI - and to engineer their thermally activated decay.

physics.comp-ph↗

arXiv2025

Entropy-driven phase transition in a non-collinear antiferromagnet due to higher-order exchange interactions

The triple-Q state arises due to the superposition of three symmetry equivalent spin spirals stabilized by higher-order exchange interactions. It has been predicted more than 20 years ago but was only recently discovered in a Mn monolayer on the Re(0001) surface. To date little is known about the thermodynamic properties of this intriguing non-coplanar spin state. Here, we reveal a low-temperature phase transition between the triple-Q and the row-wise antiferromagnetic state in this system via Monte Carlo simulations based on an atomistic spin model parametrized by density functional theory. By modeling the free energy landscape in terms of thermal excitations we derive an analytical expression of the partition function, which allows us to prove that the phase transition is driven by entropy. The predicted phase transition is not unique to Mn/Re(0001) but appears for a wide range of magnetic interaction parameters and is expected to occur also for other multi-Q states.

cond-mat.mtrl-sci↗

arXiv2025

Eigenmode following for direct entropy calculation and characterization of magnetic systems

We present an eigenmode following method (EMF) that has been developed for the numerical scanning of the potential energy surface and the direct calculation of entropy and pre-exponential factors of Arrhenius-like transition rates in the framework of transition state theory. In contrast to other methods, we do not use EMF to move "uphill" or "downhill" in energy to find stationary points, but to obtain energy curves. By numerical integration of the Boltzmann factor along these curves, the partition functions of the followed eigenmodes can be calculated without making assumptions of the form of the energy curves. The EMF method is computationally more elaborate than traditional approaches as it requires iterative updates of the respective eigenpair spectrum. In order to mitigate this increase in computational cost, the EMF method can be combined with other approaches like the harmonic approximation for all eigenmodes but the softest which typically require the most accurate mod elling. In this work we first introduce the general theoretical background and algorithm of the EMF method before providing test calculations and relevant use-cases in the framework of atomistic spin simulations with a focus on magnetic skyrmions collapse.

cond-mat.mtrl-sci↗

arXiv2025

Identification of mechanisms of magnetic transitions using an efficient method for converging on first order saddle points

A method for locating first order saddle points on the energy surface of a magnetic system is described and several applications presented where the mechanism of various magnetic transitions is identified. The starting point for the iterative search algorithm can be anywhere, even close to a local energy minimum representing an initial state of the system, and the final state need not be specified. Convergence on a saddle point is obtained by inverting the component of the gradient along the minimum mode, thereby effectively transforming the neighbourhood of the saddle point to that of a local minimum. The method requires only the lowest two eigenvalues and corresponding eigenvectors of the Hessian of the system's energy and they are found using a quasi-Newton limited-memory Broyden-Fletcher-Goldfarb-Shanno solver for the minimization of the Rayleigh quotient without explicit evaluation of the Hessian. The method is applicable to large systems as the computational effort scales linearly with system size. Applications are presented to transitions in systems that reveal significant complexity of co-existing magnetic states, such as skyrmions, skyrmion bags, skyrmion tubes, chiral bobbers, and globules. When combined with rate theory within the harmonic approximation, the method can be used for simulations of the long timescale dynamics of complex magnetic systems characterized by multiple metastable states.

physics.comp-ph↗

arXiv2024

Prediction of stable nanoscale skyrmions in monolayer Fe$_5$GeTe$_2$

Using first-principles calculations and atomistic spin simulations, we predict stable isolated skyrmions with a diameter below 10 nm in a monolayer of the two-dimensional van der Waals ferromagnet Fe$_5$GeTe$_2$, a material of significant experimental interest. A very large Dzyaloshinskii-Moriya interaction (DMI) is observed due to the intrinsic broken inversion symmetry and strong spin-orbit coupling for monolayer Fe$_5$GeTe$_2$. We show that the nearest-neighbor approximation, often used in literature, fails to describe the DMI. The strong DMI together with moderate in-plane magnetocrystalline anisotropy energy allows to stabilize nanoscale skyrmions in out-of-plane magnetic fields above $\approx 2$~T. The energy barriers of skyrmions in monolayer Fe$_5$GeTe$_2$ are comparable to those of state-of-the-art transition-metal ultra-thin films. We further predict that these nanoscale skyrmions can be stable for hours at temperatures up to 20 K.

cond-mat.mtrl-sci↗

arXiv2021

Effects of interlayer exchange on collapse mechanisms and stability of magnetic skyrmions

Theoretical calculations of thermally activated decay of skyrmions in systems comprising several magnetic monolayers are presented, with a special focus on bilayer systems. Mechanisms of skyrmion collapse are identified and corresponding energy barriers and thermal collapse rates are evaluated as functions of the interlayer exchange coupling and mutual stacking of the monolayers using transition state theory and an atomistic spin Hamiltonian. In order to contrast the results to monolayer systems, the magnetic interactions within each layer are chosen so as to mimic the well-established Pd/Fe/Ir(111) system. Even bilayer systems demonstrate a rich diversity of skyrmion collapse mechanisms that sometimes co-exist. For very weakly coupled layers, the skyrmions in each layer decay successively via radially-symmetric shrinking. Slightly larger coupling leads to an asymmetric chimera collapse stabilized by interlayer exchange. When the interlayer exchange coupling reaches a certain critical value, the skyrmions collapse simultaneously. Interestingly, the overall energy barrier for the skyrmion collapse does not always converge to a multiple of that for a monolayer system in the strongly coupled regime. For a certain stacking of the magnetic layers, the energy barrier as a function of the interlayer exchange coupling features a maximum and then decreases with the coupling strength in the strong coupling regime. Calculated mechanisms of skyrmion collapse are used to ultimately predict the skyrmion lifetime. Our results reveal a comprehensive picture of thermal stability of skyrmions in magnetic multilayers and provide a perspective for realizing skyrmions with controlled properties.

physics.comp-ph↗