Hatem Ben Mahmoud

Scalable fabrication of functional magnetic nanostructures remains a major challenge for the development of spin-wave devices and magnonic metamaterials, where nanoscale geometrical precision, reproducibility, and scalable nanopatterning are essential. In this work, we demonstrate that a mechanically stabilized Lloyd’s mirror interference lithography platform enables the reliable fabrication of periodic CoFeB magnonic nanostructures over millimeter-scale areas using a simple and cost-effective process. The optimized optical and mechanical configurations provide reproducible control of the interference conditions and allow the fabrication of one- and two-dimensional (1D and 2D) magnetic architectures with tunable lattice parameters, including nanowires, antidot lattices, dot arrays, lace-like networks, and volcano-like structures. Structural characterization by atomic force microscopy and scanning electron microscopy confirms the nanopattern transfer, while ferromagnetic resonance and Brillouin light-scattering measurements reveal a substantially modified dynamic magnetic response in the patterned structures, characterized by multiple additional resonances and a spin-wave dispersion that differs from that of the continuous film. These results establish interference lithography as a versatile and scalable route for manufacturing functional magnonic nanomaterials and spin-wave metamaterials for future wave-based information processing technologies.

We report the development and synchrotron integration of a longitudinal magneto-optical Kerr effect (MOKE) magnetometer designed for in situ operation during x-ray diffraction (XRD) experiments under multiaxial mechanical loading. The optical layout, magnetic-field geometry, and mechanical compatibility were optimized to enable synchronized acquisition of MOKE hysteresis loops, XRD lattice strain, and digital image correlation (DIC) data within the constrained environment of a diffraction goniometer. The capabilities of the platform are demonstrated on a Co/W thin film deposited on a flexible Kapton® substrate subjected to equi-biaxial tensile loading. The combined MOKE–XRD–DIC measurements reveal three distinct mechanical regimes from elastic strain transfer to partial relaxation and ultimately full mechanical fragmentation, each associated with a characteristic magnetic response. Post-mortem image analysis provides a quantitative description of fragment morphology, linking crack topology to the evolution of magnetic properties and highlighting the role of fragment size, shape anisotropy, and mechanical isolation in strain-dependent magnetic behavior. The present approach establishes a multi-scale framework that integrates surface magnetometry, structural probes, and real-space imaging, opening new opportunities for studying magneto-mechanical coupling and damage-driven functional evolution in flexible magnetic thin films.

Flexible magnetoelectronics face a major challenge in maintaining functionality under mechanical strain. This research investigates how biaxial multicracking affects the magnetic properties of nanometric thin films, specifically by separating magnetoelastic from magnetostatic effects. Using a unique experimental platform, we show that in magnetostrictive Co films, the magnetic behavior is dominated by stress‐induced magnetoelastic effects. In contrast, in non‐magnetostrictive films, the magnetic changes only appear once multicracking begins, allowing us to demonstrate the magnetostatic contributions from fragmentation. Our findings reveal that the variation in the saturation field correlates directly with fragment shape. This work demonstrates that fragmentation is not just a failure mechanism but a controllable process whose magnetic effects can be understood and leveraged for designing next‐generation flexible devices.

We explore the magnetic properties of a thin Co film deposited on Kapton® substrates using the magneto-optical Kerr effect in a longitudinal configuration. We developed a magnetometer integrated with a tensile testing machine to investigate magnetization reversal phenomena under applied strain. The tensile machine, custom-designed to fit the experimental constraints, applies uniaxial stress to the samples, facilitating the study of magnetoelastic effects. Calibration using digital image correlation ensures accurate strain measurements. Our findings demonstrate that the application of strain significantly influences the magnetization curves, highlighting the emergence of anisotropies and changes in coercive and saturation fields.

The influence of multi-cracking on the magnetic response of more (Co) or less (Ni78Fe22) magnetostrictive ferromagnetic nanofilms on flexible substrates has been studied by combining tensile tests with in situ magneto-optical Kerr effect magnetometry measurements, up to large strain (20%). The results show that the variations of the magnetic features are more significant in the elastic domain (before cracking), while they are slightly affected in the multi-cracking regime, linked to the fact that the stresses evolve relatively little in this regime. This results in a lesser modification of the magnetization curves of Ni78Fe22, which also means weak magnetostatic (dipolar) effects despite a very high crack density. This is very promising for the applicability of magnetic films in highly curved or stretched systems, especially using weakly magnetostrictive materials.