arXiv subjects

Ivan P. Miranda

Publications and source records attributed to Ivan P. Miranda.

5 recordsLinked to original sources

arXiv2026

Harnessing the skyrmion Hall effect for low-power skyrmion transport in a tubular synthetic antiferromagnet

We show that optimal control can turn the skyrmion Hall effect from a source of typically unwanted transverse motion into a mechanism for reducing Ohmic losses in skyrmion transport. We consider a pair of antiferromagnetically coupled skyrmions confined to a tubular geometry, where their relative transverse displacement becomes a periodic internal coordinate. The skyrmion Hall effect drives this coordinate, while finite interlayer coupling makes the resulting relation between applied current and longitudinal velocity nonlinear, allowing different current protocols to produce the same prescribed average velocity. We determine which of these protocols minimizes Joule heating. Depending on the interlayer coupling and spin-transfer-torque parameters, the optimal current is either constant, with the skyrmion pair maintaining a fixed relative position, or time dependent, with the pair undergoing periodic relative motion around the tube. In either case, the additional internal degree of freedom created by the skyrmion Hall effect and interlayer coupling enables skyrmion transport at a lower power than in the uncoupled limit.

cond-mat.mes-hall↗

arXiv2026

Disorder-induced chirality in superconductor-ferromagnet heterostructures revealed by neutron scattering and multiscale modeling

Chirality in superconductor-ferromagnet hybrids strongly influences phenomena such as the observable signatures of long-range triplet superconductivity, but its microscopic origin in nominally centrosymmetric ferromagnets is still unclear. Here, we combine structural characterization, polarization-analyzed grazing-incidence small-angle neutron scattering (PA-GISANS), first-principles calculations, and deep-learning-assisted multiscale modeling to study FePd and Nb/FePd heterostructures. Experimentally, we observe partial L1$_0$ order, atomic intermixing, anti-phase boundaries, and a depth-dependent defect gradient across the FePd layer, together with a finite net magnetic chirality at room temperature. The GISANS asymmetry indicates that the main chiral contribution lies in-plane, with an additional out-of-plane component associated with depth-dependent magnetic inhomogeneity. Theoretically, we show that chemical disorder in FePd, especially when combined with a compositional gradient, produces finite Dzyaloshinskii-Moriya interactions and stabilizes chiral finite-$\mathbf{q}$ magnetic modulations with mixed Bloch-N\'eel character. In the mesoscopic model, the resulting in-plane modulation length approaches the experimentally observed range. These results identify disorder and compositional gradients as intrinsic microscopic sources of net chirality in FePd-based films, showing that the observed chirality does not arise only from interface effects.

cond-mat.mtrl-sci↗

arXiv2025

Theory of Momentum-Resolved Electron Energy-Loss Spectra of Coupled Phonon and Magnon Excitations

We develop a theory of momentum-resolved electron energy-loss spectra in the scanning transmission microscope (STEM-EELS) that captures the effects of coupled phonon and magnon excitations within a unified formalism, and apply it to body-centered cubic iron at 300 K. By advancing the Time Autocorrelation of Auxiliary Wavefunctions (TACAW) method to incorporate atomistic spin-lattice dynamics (ASLD), we simulate the EELS signal, including phonon-magnon interaction effects, dynamical diffraction, and multiple scattering. Our results reveal non-additive spectral features arising from phonon-magnon coupling, hybridization, and energy shifts, and further allow estimation of the electron dose required to detect magnon scattering under optimized detector conditions.

cond-mat.mtrl-sci↗

arXiv2024

Optimal field-free magnetization switching via spin-orbit torque on the surface of a topological insulator

We present an optimal field-free protocol for current-induced switching of a perpendicularly magnetized ferromagnetic insulator nanoelement on the surface of a topological insulator. The time dependence of in-plane components of the surface current, which drives the magnetization reversal via the Dirac spin-orbit torque with minimal Joule heating, is derived analytically as a function of the switching time and material properties. Our analysis identifies that energy-efficient switching is achieved for vanishing damping-like torque. The optimal reversal time that balances switching speed and energy efficiency is determined. When we compare topological insulators to heavy-metal systems, we find similar switching costs for the optimal ratio between the spin-orbit torque coefficients. However, topological insulators offer the advantage of tunable material properties. Finally, we propose a robust and efficient simplified switching protocol using a down-chirped rotating current pulse, tailored to realistic ferromagnetic/topological insulator systems.

cond-mat.mes-hall↗

arXiv2024

Quantum analog of Landau-Lifshitz-Gilbert dynamics

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 entangled, our study uncovers an unusual form of revival-type quantum correlation dynamics, which differs significantly from what is typically seen in open quantum systems.

quant-ph↗