arXiv subjects

Colin Ducarme

Publications and source records attributed to Colin Ducarme.

3 recordsLinked to original sources

arXiv2026

Beyond binary at submicron dimensions: crossed-ellipse MTJ free layers as multi-state cells for spintronic crossbars

Spintronic crossbars are promising hardware platforms for energy-efficient neuromorphic computing, but conventional magnetic tunnel junctions (MTJs) are binary, limiting the information density and synaptic precision of each crosspoint. Here, MuMax3 micromagnetic simulations are used to investigate how size and aspect ratio control the switching and remanent-state landscape of crossed-ellipse MTJ free layers, with permalloy as the main model system and CoFeB checks for transferability. At fixed 8:1 aspect ratio, shrinking the device from 16 micron x 2 micron to 80 nm x 10 nm lowers the absolute switching current but raises the switching field from about 11 Oe to about 301 Oe and increases the SOT current density. At fixed major axis 1.6 micron, aspect-ratio tuning produces a low-field four-state regime, while lower aspect ratios stabilize additional remanent states with lower switching fields and current densities. A 1.6 micron x 0.8 micron device exhibits twelve accessible remanent plateaus in its angle-resolved planar Hall response, with the resolved state count depending on both aspect ratio and absolute size. Projected MTJ readout gives multiple electrical levels, while minimum-energy-path calculations show that the twelve configurations are not all thermally independent. Independent MuMax+ calculations reproduce the multistate topology and reveal lower-barrier multistep escape pathways between nominally distant states. These results define a geometry-dependent design window for scalable multistate spintronic crossbar cells.

cond-mat.mtrl-sci↗

arXiv2026

Data-Driven Thiele Equation Approach for State-Dependent Coefficients in the Nonlinear Dynamics of Vortex-based Nano-Oscillators

Spin-torque vortex oscillators provide a model system for the nonlinear dynamics of a confined magnetic texture. Their motion is commonly described by the Thiele equation, but its standard constant-coefficient form relies on a rigid-texture approximation and becomes inaccurate at large gyration amplitudes. We introduce a data-driven Thiele equation approach (DD-TEA) that extracts effective, position-dependent Thiele coefficients from a single current-ramp micromagnetic simulation by interpolating the magnetization in vortex-core-position space. The extracted maps reveal a weak increase of the gyrovector magnitude and a pronounced separation of the radial and azimuthal dissipation as the orbit expands, providing quantitative signatures of confinement- and motion-induced vortex deformation. Because the gyrotropic, dissipative, conservative, and spin-transfer contributions retain their usual Thiele structure, the resulting description remains physically interpretable rather than acting as a black-box surrogate. Incorporating these state-dependent coefficients into the equation reproduces the nonlinear stable-orbit dynamics and accurately predicts the response to time-varying currents, whereas a conventional constant-coefficient description predicts vortex expulsion. The framework therefore provides a systematic route for deriving effective collective-coordinate dynamics from full micromagnetic states with high computational efficiency

cond-mat.mes-hall↗

arXiv2026

The Deformed Image Vortex Ansatz: A Perturbation-Aware Description of Magnetic Vortices in In-Plane Fields

Thiele-based descriptions of magnetic vortex dynamics in thin ferromagnetic nanodots rely on magnetization ansätze that describe the equilibrium texture but cannot represent perturbation-induced deformations. We introduce the Deformed Image Vortex Ansatz (DIVA): a perturbation-aware ansatz in which the response to an external perturbation is built into the magnetization profile itself, rather than appended to the dynamics as a correction. Here, we demonstrate the concept for a uniform, stationary in-plane field applied to a Permalloy nanodot, for which the deformation is analytically tractable. A symmetry-based perturbative expansion identifies the leading deformation as a single $m = 1$ harmonic around the disk, while energy minimization and a dominant-balance analysis yield a closed-form interpolant for the radial profile. Benchmarked against micromagnetic simulations on Permalloy disks of aspect ratio $t/R = 0.1$ and $0.0125$, this realization reduces the disk-averaged angular deviation by a factor of 3 to 6 relative to the two-vortex ansatz, depending on geometry and field, and reduces the total-energy deviation by about a factor of six in the thicker disk.

cond-mat.mes-hall↗