Facultat de Física

Departament de Física de la Matèria Condensada

Wrinkled magnetic thin films towards magnonics

Dr. Regina Galceran Vercher

Departament de Física Aplicada -- Universitat de Barcelona

Magnonic crystals are magnetic metamaterials engineered to control and manipulate spin waves, or magnons. These magnons — collective excitations of electron spins — are promising for data transmission and processing due to their low energy consumption and compatibility with standard CMOS technology. Their propagation can be tailored by introducing periodic artificial structures at the micro- and nanoscale in magnetic materials, typically fabricated through complex lithographic techniques. However, in certain systems, periodic structures can arise spontaneously when flexible substrates are used. Under compressive strain, these substrates form surface wrinkles as a mechanical response. Such wrinkles can be deliberately induced during the deposition of a thin film onto a pre-stretched elastomer substrate, often as a strategy to enhance mechanical durability. In magnetic thin films, these wrinkles also modify magnetic properties through strain-induced effects. Notably, the wrinkle wavelengths — ranging from tens of nanometers to several micrometers — are well-matched to the characteristic wavelengths of spin waves in ferromagnetic media. In our work, we explore the wrinkling of magnetic thin films deposited on flexible polymer substrates, proposing them as a cost-effective and scalable alternative platform for magnonic systems — bypassing the need for conventional lithographic patterning. We demonstrate that these wrinkles significantly affect magnetic anisotropy, as characterized via magneto-optical Kerr effect microscopy and ferromagnetic resonance. Furthermore, we examine how the wrinkle patterns respond to external mechanical stress, revealing a bistable orientation behavior. This mechanical bistability opens new avenues for tunable magnonic device functionalities. Lastly, micromagnetic simulations provide insight into spin-wave dispersion within these wrinkled films, highlighting their potential for adaptable and scalable magnonic applications.