arXiv subjects

A. Hierro-Rodríguez

Publications and source records attributed to A. Hierro-Rodríguez.

6 recordsLinked to original sources

arXiv2025

Nucleation of magnetic textures in stripe domain bifurcations for reconfigurable domain wall racetracks

Within the racetrack memory paradigm, systems exploiting magnetic guiding potentials instead of geometrical ones, allow for enhancing the versatility of the final devices adding magnetic reconfigurable capabilities. Hard/soft magnetic multilayers with stripe domain configurations fulfill these requirements. In these systems, the topology of the generated textures that would act as information carriers, is strongly conditioned by the stripe lattice configuration. Micromagnetic simulations have been used to study the magnetization reversal process in NdCo$_5$/Py reconfigurable racetracks. By using skyrmionic charges and magnetic vorticity lines, the topological transformations controlling the nucleation of vortices, antivortices, Bloch lines and Bloch points has been analyzed. It has been shown that magnetic topological charge exchanges between textures rule the formation of vortex/antivortex pairs with opposite polarities, key for the guided propagation through the stripe pattern.

cond-mat.mtrl-sci↗

arXiv2024

Remote-sensing based control of 3D magnetic fields using machine learning for in-operando applications

In-operando techniques enable real-time measurement of intricate physical properties at the micro- and nano-scale under external stimuli, allowing the study of a wide range of materials and functionalities. In nanomagnetism, in-operando techniques greatly benefit from precise three-dimensional (3D) magnetic field control, enabling access to complex magnetic states forming in systems where multiple energies are set to compete with each other. However, achieving such precision is challenging and uncommon, as specific applications impose constraints on the type and geometry of magnetic field sources, limiting their capabilities. Here, we introduce an approach that leverages machine learning algorithms to achieve precise 3D magnetic field control using a hexapole electromagnet that is composed of three independent, non-collinear dipole electromagnets. In our experimental setup, magnetic field sensors are placed at a distance from the sample position due to inherent constraints, leading to indirect field measurements that differ from the magnetic field experienced by the sample. We find that the existing relationship between the remote and sample frames of reference is non-linear, thus requiring a more complex calibration method. To address this, we employ a multi-layer perceptron neural network that processes multiple inputs from a dynamic magnetic field sequence, effectively capturing the time-dependent non-linear field response. The network achieves high calibration accuracy and demonstrates exceptional generalization to unseen magnetic field sequences. This study highlights the significant potential of machine learning in achieving high-precision control and calibration, crucial for in-operando experiments where direct measurement at the point of interest is not possible.

physics.app-ph↗

arXiv2024

Preservation of scalar spin chirality across a metallic spacer in synthetic antiferromagnets with chiral interlayer interactions

Chiral magnetic textures are key for the development of modern spintronic devices. In multilayered thin films, these are typically stabilized via the interfacial intralayer Dzyaloshinskii-Moriya interaction (DMI). Additionally, it has been recently observed that DMI may also promote vector spin chirality along the third dimension, coupling spins in different magnetic layers via non-magnetic spacer layers, an effect referred to as interlayer DMI (IL-DMI). This interaction holds promise for 3D nanomagnetism, from the creation of 3D spin structures such as hopfions to new forms of magnetic functionality in the vertical direction via remote control of chiral spin states. Here, we investigate via magnetic X-ray scattering and imaging techniques the chiral nature of orthogonal magnetic states that form in a synthetic antiferromagnet with IL-DMI. We find that the vector spin chirality of the textures formed in an in-plane layer is determined by the net out-of-plane spin configuration of a neighboring layer, leading as a result to complex spin states across a metallic interface where the overall scalar spin chirality is preserved. This work thus uncovers a new flavor of chiral interlayer interactions, demonstrating new ways to control magnetic chirality in three dimensions.

cond-mat.mes-hall↗

arXiv2024

Determination of optimal experimental conditions for accurate 3D reconstruction of the magnetization vector via XMCD-PEEM

In this work we present a detailed analysis on the performance of X-ray magnetic circular dichroism photo-emission electron microscopy (XMCD-PEEM) as a tool for vector reconstruction of the magnetization. For this, we choose 360$^{\circ}$ domain wall ring structures which form in a synthetic antiferromagnet as our model to conduct the quantitative analysis. We assess how the quality of the results is affected depending on the number of projections that are involved in the reconstruction process, as well as their angular distribution. For this we develop a self-consistent error metric, which indicates that the main factor of improvement comes from selecting the projections evenly spread out in space, over having a larger number of these spanning a smaller angular range. This work thus poses XMCD-PEEM as a powerful tool for vector imaging of complex 3D magnetic structures.

cond-mat.mes-hall↗

arXiv2022

Fourier-space generalized magneto-optical ellipsometry

The magneto-optical Kerr effect (MOKE) is a widely used lab-based technique for the study of thin films and nanostructures, providing magnetic characterization with good spatial and temporal resolutions. Due to the complex coupling of light with a magnetic sample, conventional MOKE magnetometers normally work by selecting a small range of incident wave-vector values, focusing the incident light beam to a small spot, and recording the reflected intensity at that angular range by means of photodetectors. This generally provides signals proportional to a mixture of magnetization components, requiring additional methodologies for full vectorial magnetic characterization. Here, we computationally investigate a Fourier-space MOKE setup, where a focused beam ellipsometer using high numerical aperture optics and a camera detector is employed to simultaneously map the intensity distribution for a wide range of incident and reflected wave-vectors. We employ circularly incident polarized light and no analyzing optics, in combination with a fitting procedure of the light intensity maps to the analytical expression of the Kerr effect under linear approximation. In this way, we are able to retrieve the three unknown components of the magnetization vector as well as the material's optical and magneto-optical constants with high accuracy and short acquisition times, with the possibility of single shot measurements. Fourier MOKE is thus proposed as a powerful method to perform generalized magneto-optical ellipsometry for a wide range of magnetic materials and devices.

physics.app-ph↗

arXiv2021

Adjustable 3D magnetic configuration in ferrimagnetic multilayers with competing interactions visualized by soft X-ray vector tomography

Soft X-ray magnetic vector tomography has been used to visualize with unprecedented detail and solely from experimental data the 3D magnetic configuration of a ferrimagnetic Gd12Co88/Nd17Co83/Gd24Co76 multilayer with competing anisotropy, exchange and magnetostatic interactions at different depths. The trilayer displays magnetic stripe domains, arranged in a chevron pattern, which are imprinted from the central Nd17Co83 into the bottom Gd12Co88 layer with a distorted closure domain structure across the thickness. Near the top Gd24Co76 layer, local exchange springs with out-of-plane magnetization reversal, modulated ripple patterns and magnetic vortices and antivortices across the thickness are observed. The detailed analysis of the magnetic tomogram shows that the effective strength of the exchange spring at the NdCo/GdCo interface can be finely tuned by GdxCo1-x composition and anisotropy (determined by sample fabrication) and in-plane stripe orientation (adjustable), demonstrating the capability of 3D magnetic visualization techniques in magnetic engineering research.

cond-mat.mtrl-sci↗