arXiv subjects

Riccardo Battistelli

Publications and source records attributed to Riccardo Battistelli.

5 recordsLinked to original sources

arXiv2026

Emergent Chaos-Like Dynamics of Spin-Orbit Torque-Driven Magnetic Transitions

Spin-orbit torques (SOTs) are widely used to control magnetization in nanoscale electric systems and are typically assumed to drive skyrmion nucleation and motion in a deterministic manner, especially in materials with strong Dzyaloshinskii-Moriya interaction. Here, using time-resolved holography-based x-ray microscopy supported by micromagnetic simulations, we reveal that on nano- to picosecond timescales the actual dynamics can deviate strikingly from this expectation by producing transient regimes of chaos-like behavior. By exploiting deterministic skyrmion generation at an anisotropy-engineered defect and implementing a high-resolution pump-probe scheme, we directly track the magnetization evolution in real space. This approach uncovers a dynamic phase transition that separates coherent SOT-driven motion from a regime of transient instability characterized by picosecond-scale fluctuations, strong domain disorder, topological instabilities, and skyrmion shedding, experimentally observed here for the first time. During SOT actuation, the system briefly enters this instability regime, showing short-lived chaos-like behavior, yet it reliably relaxes into robust and reproducible final states. Our results demonstrate a powerful methodology for accessing time-averaged nano- to picosecond dynamics in magnetic systems and reveal a previously hidden layer of transient, topologically rich behavior underlying nominally deterministic skyrmion control.

cond-mat.mes-hall↗

arXiv2026

3D tomographic imaging of skyrmionic cocoons using HERALDO

Uncovering the rich and intricate characteristics of three-dimensional (3D) magnetic textures is essential for functional materials such as magnetic multilayers, where the delicate balance of various magnetic interactions leads to complex 3D spin arrangements. Among these textures, skyrmionic cocoons-tubular 3D magnetic structures characterized by a closed magnetization surface wrapping around a core-have emerged as particularly intriguing. Stabilized by competing magnetic interactions, these textures reside within a fraction of the thickness of the magnetic material and exhibit a typical lateral size of approximately 100 nm. Here, we present a vector tomographic reconstruction of the 3D magnetization in aperiodic Pt/Co/Al chiral multilayers, where skyrmionic cocoons have been recently reported. Using soft X-ray Holography with Extended Reference by Autocorrelation Linear Differential Operator (HERALDO), we acquire tomographic projections of the magnetic configuration and reconstruct the full 3D magnetization vector field with a spatial resolution of approximately 30 nm, as determined by Fourier shell correlation (FSC). This resolution allows us to observe critical features of the cocoons, such as their vertical misalignment and their overall chirality. Our findings demonstrate that HERALDO-based vector tomography is a powerful approach for revealing the internal structure and vertical extent of these nanoscale magnetic textures, offering new experimental insights into their intrinsic behavior.

cond-mat.mtrl-sci↗

arXiv2025

A fluctuation-free pathway for a topological magnetic phase transition

Topological magnetic textures are particle-like spin configurations stabilized by competing interactions. Their formation is commonly attributed to fluctuation-driven, first-order nucleation processes requiring activation over a topological energy barrier. Here, we demonstrate an alternative barrier- and fluctuation-free pathway for nucleating topological magnetic textures, triggered in our experiments by an excitation-induced spin reorientation transition. By combining x-ray imaging, scattering and micromagnetic simulations, we show that the system follows a deterministic cascade of symmetry-breaking phase transitions after excitation. First, the system undergoes a second-order phase transition from a homogeneous state to weak stripe domains, then a first-order transition to topologically trivial bubbles, and finally a topological switching event into skyrmionic textures. Through simulations, we generalize our findings and demonstrate that this pathway is active in a vast range of low-anisotropy materials. This previously unrecognized, spontaneous transition pathway suggests strategies for rapid, low-energy generation of topological spin textures and points to a general role of intrinsic modulational instabilities in phase transitions beyond magnetism.

cond-mat.mtrl-sci↗

arXiv2025

Picosecond localization dynamics following ultrafast nanoscale magnetic switching

Ultrashort laser pulses provide the fastest known way to switch magnetic order. Such excitation commonly creates nanometer-scale domains, even after homogeneous illumination when the position of nucleated domains is not externally defined. However, the physics of domain localization during such ultrafast phase transitions remains unresolved. Here, we use shot-resolved pump-probe resonant x-ray scattering together with a material featuring a periodically modulated magnetic anisotropy landscape to track, in real time, the laser-driven nucleation and localization of nanometer-scale spin textures. We find that nucleation and localization are two distinct processes. Nucleation occurs homogeneously via fluctuations at early times, whereas spatially periodic structures emerge only later and, under suitable conditions, localize in less than one nanosecond. Real-space simulations show that this localization is governed by strong lateral variations in spin-texture lifetimes. Our results demonstrate that ultrafast phase-transition dynamics fundamentally differ from conventional transitions, yet still can be controlled through moderate nanometer-scale tailoring of the energy landscape.

cond-mat.mes-hall↗

arXiv2023

Coherent x-ray magnetic imaging with 5 nm resolution

Soft x-ray microscopy plays an important role in modern spintronics. However, the achievable resolution of most x-ray magnetic imaging experiments is above 10 nm, limiting access to fundamental and technologically relevant length scales. Here, we demonstrate x-ray magnetic microscopy with 5 nm resolution by combining holography-assisted coherent diffractive imaging with heterodyne amplification of the weak magnetic signal. The gain in resolution and contrast allows direct access to key magnetic properties, including domain wall profiles and the position of pinning sites. The ability to detect and map such properties with photons opens new horizons for element-specific, time-resolved, and in-operando research on magnetic materials and beyond.

cond-mat.mtrl-sci↗