arXiv subjects

Swapneel Amit Pathak

Publications and source records attributed to Swapneel Amit Pathak.

6 recordsLinked to original sources

arXiv2026

Eigenmodes of synthetic antiferromagnetic skyrmions

We investigate the excitation modes of confined synthetic-antiferromagnetic (SAF) skyrmions using micromagnetic eigenvalue and ringdown simulations. Starting from a single skyrmion in a ferromagnetic layer, where the lowest-frequency modes are a gyrotropic and a breathing mode, we study how antiferromagnetic interlayer coupling modifies the dynamics in SAF bilayers. We consider several geometries: single SAF skyrmions in square and rectangular confinement, unequal layer thicknesses, and strips containing multiple skyrmions. The antiferromagnetic coupling strongly modifies the low-frequency dynamics. The square geometry exhibits two nearly degenerate gyrotropic modes, where in each both layers have the same rotation sense. In rectangular geometries, we instead find nearly linear SAF skyrmion translation emerging from opposite gyration sense in the two layers. These translational modes become the characteristic low-frequency excitations of SAF skyrmion chains. For skyrmion chains, we identify collective translational and breathing modes with standing-wave-like spatial profiles. Beyond ferromagnetic-like breathing modes, the SAF geometry supports breathing oscillations in which the two layers oscillate out of phase. We further demonstrate signal propagation along extended SAF skyrmion chains with propagation velocities comparable to ferromagnetic skyrmion chains. These results provide a systematic description of the collective dynamics of SAF skyrmions arising from the interplay of geometric confinement, intralayer, and interlayer coupling.

cond-mat.mes-hall↗

arXiv2024

NeuralMag: an open-source nodal finite-difference code for inverse micromagnetics

We present NeuralMag, a flexible and high-performance open-source Python library for micromagnetic simulations. NeuralMag leverages modern machine learning frameworks, such as PyTorch and JAX, to perform efficient tensor operations on various parallel hardware, including CPUs, GPUs, and TPUs. The library implements a novel nodal finite-difference discretization scheme that provides improved accuracy over traditional finite-difference methods without increasing computational complexity. NeuralMag is particularly well-suited for solving inverse problems, especially those with time-dependent objectives, thanks to its automatic differentiation capabilities. Performance benchmarks show that NeuralMag is competitive with state-of-the-art simulation codes while offering enhanced flexibility through its Python interface and integration with high-level computational backends.

physics.comp-ph↗

arXiv2024

Numerical simulation projects in micromagnetics with Jupyter

We report a case study where an existing materials science course was modified to include numerical simulation projects on the micromagnetic behavior of materials. The Ubermag micromagnetic simulation software package is used in order to solve problems computationally. The simulation software is controlled through Python code in Jupyter notebooks. Our experience is that the self-paced problem-solving nature of the project work can facilitate a better in-depth exploration of the course contents. We discuss which aspects of the Ubermag and the project Jupyter ecosystem have been beneficial for the students' learning experience and which could be transferred to similar teaching activities in other subject areas.

physics.ed-ph↗

arXiv2023

Controlling stable Bloch points with electric currents

The Bloch point is a point singularity in the magnetisation configuration, where the magnetisation vanishes. It can exist as an equilibrium configuration and plays an important role in many magnetisation reversal processes. In the present work, we focus on manipulating Bloch points in a system that can host stable Bloch points - a two-layer FeGe nanostrip with opposite chirality of the two layers. We drive Bloch points using spin-transfer torques and find that Bloch points can move collectively without any Hall effect and report that Bloch points are repelled from the sample boundaries and each other. We study pinning of Bloch points at wedge-shaped constrictions (notches) in the nanostrip and demonstrate that arrays of Bloch points can be moved past a series of notches in a controlled manner by applying consecutive current pulses of different strength. Finally, we simulate a T-shaped geometry and demonstrate that a Bloch point can be moved along different paths by applying current between suitable strip ends.

cond-mat.mes-hall↗

arXiv2021

Geometrically constrained Skyrmions

Skyrmions are chiral swirling magnetization structures with nanoscale size. These structures have attracted considerable attention due to their topological stability and promising applicability in nanodevices, since they can be displaced with spin-polarized currents. However, for the comprehensive implementation of skyrmions in devices, it is imperative to also attain control over their geometrical position. Here we show that, through thickness modulations introduced in the host material, it is possible to constrain three-dimensional skyrmions to desired regions. We investigate skyrmion structures in rectangular FeGe platelets with micromagnetic finite element element simulations. First, we establish a phase diagram of the minimum-energy magnetic state as a function of the external magnetic field strength and the film thickness. Using this understanding, we generate preferential sites for skyrmions in the material by introducing dot-like "pockets" of reduced film thickness. We show that these pockets can serve as pinning centers for the skyrmions, thus making it possible to obtain a geometric control of the skyrmion position. This control allows stabilizing skyrmions at positions and in configurations that they would otherwise not attain. Our findings may have implications for technological applications in which skyrmions are used as units of information that are displaced along racetrack-type shift register devices.

cond-mat.mes-hall↗

arXiv2020

Three-Dimensional Chiral Magnetization Structures in FeGe Nanospheres

Skyrmions, spin spirals, and other chiral magnetization structures developing in materials with intrinsic Dzyaloshinsky-Moriya Interaction display unique properties that have been the subject of intense research in thin-film geometries. Here we study the formation of three-dimensional chiral magnetization structures in FeGe nanospheres by means of micromagnetic finite-element simulations. In spite of the deep sub-micron particle size, we find a surprisingly large number of distinct equilibrium states, namely, helical, meron, skyrmion, chiral-bobber and quasi-saturation state. The distribution of these states is summarized in a phase diagram displaying the ground state as a function of the external field and particle radius. This unusual multiplicity of possible magnetization states in individual nanoparticles could be a useful feature for multi-state memory devices. We also show that the magneto-dipolar interaction is almost negligible in these systems, which suggests that the particles could be arranged at high density without experiencing unwanted coupling.

cond-mat.mes-hall↗