arXiv subjects

Aurelio Hierro-Rodríguez

Publications and source records attributed to Aurelio Hierro-Rodríguez.

6 recordsLinked to original sources

arXiv2026

Geometrical Confinement of Magnetic Domains and Domain Walls on Two-Dimensional Cylindrical-Shaped Ferromagnetic Surfaces

The rolling of two-dimensional (2D) van der Waals (vdW) magnetic monolayers into cylindrical architectures provides an ideal platform for confining magnetic domain walls (DWs) without edge-pinning effects. Here, we present a combined analytical and numerical investigation of DW confinement and interaction in ferromagnetic (FM) nanotubes. Using an analytical Heisenberg model on a 2D rectangular lattice, we show that transversal curvature introduces an azimuthal exchange energy penalty that intrinsically compresses the DW width. This model demonstrates excellent quantitative agreement with atomistic Landau-Lifshitz-Gilbert (LLG) spin dynamics simulations. By extending our study to realistic CrSBr (CSB) nanotubes, we model a bound state of two interacting DWs arising from a balance between long-range dipolar attraction and short-range exchange repulsion. Micromagnetic simulations reveal a non-monotonic evolution of the inter-wall distance with the tube perimeter. These findings highlight vdW magnetic nanotubes as robust platforms for stable domain confinement in quasi-one-dimensional spintronic architectures.

cond-mat.mtrl-sci↗

arXiv2025

Unidirectional motion of topological defects mediating continuous rotation processes

Topological defects play a critical role across many fields, mediating phase transitions and macroscopic behaviors as they move through space. Their role as robust information carriers has also generated much attention. However, controlling their motion remains challenging, especially towards achieving motion along well-defined paths which typically require predefined structural patterning. Here we demonstrate the tunable, unidirectional motion of topological defects, specifically magnetic dislocations in a weak magnetic stripe pattern, induced by external magnetic field in a laterally unconfined thin film. This motion is shown to mediate the overall continuous rotation of the stripe pattern. We determine the connection between the unidirectional motion of dislocations and the underlying three-dimensional (3D) magnetic structure by performing 3D magnetic vectorial imaging with in situ magnetic fields. A minimal model for dislocations in stripe patterns that encodes the symmetry breaking induced by the external magnetic field reproduces the motion of dislocations that facilitate the 2D rotation of the stripes, highlighting the universality of the phenomenon. This work establishes a framework for studying the field-driven behavior of topological textures and designing materials that enable well defined, controlled motion of defects in unconfined systems, paving the way to manipulate information carriers in higher-dimensional systems.

cond-mat.mes-hall↗

arXiv2024

Strain-induced dynamic control over the population of quantum emitters in two-dimensional materials

The discovery of quantum emitters (QEs) in two-dimensional materials (2D) has triggered a surge of research to assess their suitability for quantum photonics. While their microscopic origin is still the subject of intense studies, position-controlled QEs are routinely fabricated using static strain gradients, which are used to drive excitons towards localized regions of the crystal where quantum light emission takes place. However, the use of strain in a dynamic fashion to control the brightness of single-photon sources in 2D materials has not been explored so far. In this work, we address this challenge by introducing a novel hybrid semiconductorpiezoelectric device in which WSe2 monolayers are integrated onto piezoelectric pillars that provide both static and dynamic strains. The static strains are first used to induce the formation of QEs, whose emission shows photon anti-bunching. Their energy and brightness are then controlled via the application of voltages to the piezoelectric pillars. Numerical simulations combined with drift-diffusion equations show that these effects are due to a strain-induced modification of the confining-potential landscape, which in turn leads to a net redistribution of excitons among the different QEs. Our work provides a method to dynamically control the brightness of single photon sources based on 2D materials.

cond-mat.mtrl-sci↗

arXiv2024

Memory effects on the current induced propagation of spin textures in NdCo$_5$/Ni$_8$Fe$_2$ bilayers

Bilayers of NdCo$_5$/Ni$_8$Fe$_2$ can act as reconfigurable racetracks thanks to the parallel stripe domain configuration present in the hard magnetic material with weak perpendicular anisotropy (NdCo$_5$), and its imprint on the soft magnetic layer (Ni$_8$Fe$_2$). This pattern hosts spin textures with well defined topological charges and establishes paths for their deterministic propagation under the effect of pulsed currents, which has been studied as a function of externally applied fields by using Magnetic Transmission X-ray Microscopy. The experiments show guided vortex/antivortex propagation events within the Ni$_8$Fe$_2$ above a threshold current of $3\cdot10^{11}$ A/m$^2$. Opposite propagation senses have been observed depending on the topological charge of the spin texture, both in the remnant state and under an applied external field. Micromagnetic simulations of our multilayer reveal that the guiding effect and asymmetric propagation sense are due to the magnetic history of the hard magnetic layer. An exchange-bias-based memory effect acts as a magnetic spring and controls the propagation sense by favoring a specific orientation of the in plane magnetization, leading to a system which behaves as a hard-soft magnetic composite with reconfigurable capabilities for a controlled propagation of magnetic topological textures.

cond-mat.mtrl-sci↗

arXiv2023

Hyperbolic Bloch points in ferrimagnetic exchange spring

Bloch points in magnetic materials are attractive entities in view of magnetic information transport. Here, Bloch point configuration has been investigated and experimentally determined in a magnetic trilayer ($Gd_{12}Co_{88}/Nd_{17}Co_{83}/Gd_{24}Co_{76}$) with carefully adjusted composition within the ferrimagnetic $Gd_{x}Co_{1-x}$ alloys in order to engineer saturation magnetization, exchange length, and interlayer couplings (ferromagnetic vs antiferromagnetic). X-ray vector magnetic tomography has allowed us to determine experimentally Bloch point polarity (related to topological charge) and Bloch point helicity $γ$ (determined by magnetostatic energy). At the bottom layer (close to the ferromagnetic interface), Bloch points adopt a standard circulating configuration with helicity $γ$ close to $π/2$. Within the top layer (with much lower saturation magnetization), Bloch points nucleate within a Neel-like exchange spring domain wall created by the antiferromagnetic coupling and adopt an uncommon hyperbolic configuration, characterized by much larger helicity angles. Our results indicate a path for Bloch point engineering in future applications adjusting material parameters and domain wall characteristics.

cond-mat.mes-hall↗

arXiv2019

Tunable ferromagnetic resonance in coupled trilayers with crossed in-plane and perpendicular magnetic anisotropies

A novel approach to tune the ferromagnetic resonance frequency of a soft magnetic Ni$_{80}$Fe$_{20}$ (Permalloy = Py) film with in-plane magnetic anisotropy (IMA) based on the controlled coupling to a hard magnetic NdCo$_\text{x}$ film with perpendicular magnetic anisotropy (PMA) through a non-magnetic Al spacer is studied. Using transverse magneto-optical Kerr effect (TMOKE), alternating gradient magnetometry (AGM) as well as vector network analyzer ferromagnetic resonance (VNA-FMR) spectroscopy, the influence of both Co concentration and Al spacer thickness on the static and dynamic magnetic properties of the coupled IMA/PMA system is investigated. Compared to a single Py film, two striking effects of the coupling between IMA and PMA layers can be observed in their FMR spectra. First, there is a significant increase in the zero-field resonance frequency from 1.3 GHz up to 6.6 GHz, and second, an additional frequency hysteresis occurs at low magnetic fields applied along the hard axis. The maximum frequency difference between the frequency branches for increasing and decreasing magnetic field is as high as 1 GHz, corresponding to a tunability of about 20% at external fields of typically less than $\pm$70 mT. The origin of the observed features in the FMR spectra is discussed by means of magnetization reversal curves.

cond-mat.mes-hall↗