Bad neighbour, good neighbour: how magnetic dipole interactions between soft and hard ferrimagnetic nanoparticles affect macroscopic magnetic properties in ferrofluids
Niéli Daffé, Jovana Zečević, K. N. Trohidou, Marcin Sikora, Mauro Rovezzi, Claire Carvallo, Marianna Vasilakaki, Sophie Neveu, Johannes D. Meeldijk, Nadejda Bouldi, Véronica Gavrilov, Yohan Guyodo, Fadi Choueikani, Vincent Dupuis, Dario Taverna, Philippe Sainctavit, Amélie Juhin
Abstract
Fluids responding to magnetic fields (ferrofluids) offer a scene with no equivalent in nature to explore long-range magnetic dipole interactions. Here, we studied the very original class of binary ferrofluids, embedding soft and hard ferrimagnetic nanoparticles. We used a combination of X-ray magnetic spectroscopy measurements supported by multi-scale experimental techniques and Monte-Carlo simulations to unveil the origin of the emergent macroscopic magnetic properties of the binary mixture. We found that the association of soft and hard magnetic nanoparticles in the fluid has a considerable influence on their inherent magnetic properties. While the ferrofluid remains in a single phase, magnetic interactions at the nanoscale between both types of particles induce a modification of their respective coercive fields. By connecting the microscopic properties of binary ferrofluids containing small particles, our findings lay the groundwork for the manipulation of magnetic interactions between particles at the nanometer scale in magnetic liquids.