Magnetic nanoparticles are commonly used in biomedical applications, but the large dispersion of their properties can be problematic for some applications. This internship aims at exploiting magnetic forces at the microscale for purification and separation of magnetic nanoparticles within a microfluidic channel. Micromagnets will be synthesized and integrated into microfluidic chips in order to control finely the trajectories of magnetic particles according to their physical properties (size, magnetic moment, susceptibilty) and therefore make their separation possible.

The demand for high performance magnets is continuously growing, in particular for the green energy transition (windmills, (hybrid)-electric-vehicles, electric bicycles) but also for robotics. The present reliance on critical rare earth (RE) elements in such magnets is not sustainable. The aim of this internship is to study new magnetic materials based on a combinatorial approach in which magnetic films are fabricated with gradients of composition . The production of a very large number of samples at once, combined with high throughput characterization (composition, crystal structure and magnetic properties) allows for a fast screening of a large composition space. Furthermore, the produced data will be used to feed machine learning algorithms in order to guide the development of more sustainable permanent magnets.

The magnetisation of thin films can be manipulated not only by magnetic field but also by an electrical current through the so-called spin transfer torque effects. The dynamics of domain walls – the regions that separate magnetic domains- depends on their internal structure: this is determined by the balance between different energy terms i.e. exchange, anisotropy and magnetostatic. In non-centrosymmetric thin films where the magnetic layer is deposited on a heavy metal with large spin-orbit interaction,  the presence of interfacial Dzyaloshinskii interaction (DMI) can stabilise magnetic structures with a fixed chirality, skyrmions and domain walls with Néel internal spin structure. The current- and field-driven dynamics of such objects strongly depends on the strength of the DMI. In view of possible applications to spintronic devices, it is important to measure and optimize such interaction.

Le projet explore, avec des réseaux moléculaires, des Hamiltoniens de spin frustrés et les diagrammes de phases intriguants auxquels ils donnent accès, où l’on attend des phases exotiques de la matière, des transitions de phases non conventionnelles et où des effets de topologie peuvent se manifester.