Abstract:

We consider a dilute ensemble of randomly-oriented spherical nanomagnets and investigate its magnetization structure and ensuing neutron-scattering response by numerically solving the Landau-Lifshitz equation. Taking into account the isotropic exchange interaction, an uniaxial magnetic core anisotropy, an external magnetic field, and in particular the Néel surface anisotropy, we compute the magnetic small-angle neutron scattering cross section and pair-distance distribution function from the obtained equilibrium spin structures. The numerical results are compared to the well- known analytical expressions for uniformly magnetized particles and provide guidance to the experimentalist. Moreover, the (directed) Néel surface anisotropy is compared to a random surface anisotropy, and the effect of a particle- size distribution function is modeled. The following figure illustrates some of our simulation results for the magnetic SANS cross section of spherical nanoparticles with different types of surface anisotropy.

Bio:

At the beginning of his professional career (2008-2012), Michael Adams went through a 3.5 year long vocational training to become an electronics technician for operating technology. In 2013, he achieved a technical diploma at the Harald-Fissler school in Idar-Oberstein, Germany. Michael Adams then continued with a Bachelor (2013-2017) and Master (2017-2020) degree in electrical engineering at the University of Applied Sciences in Trier, Germany, where he focused on computational electrodynamics. In his master thesis, he worked in the group of Professor Hellmut Hupe on Langevin dynamics simulations of a system of magnetic nanoparticles in a thermal bath. In summer 2021, he received a PhD grant from the National Research Fund of Luxembourg and started his PhD project at the University of Luxembourg in the group of Professor Andreas Michels (October 2021). The topic of his PhD project is related to the understanding of magnetic small-angle neutron scattering from magnetic nanoparticles using atomistic simulations and analytical calculations.