Michael Adams

PhD student, Univ. Luxembourg

Title:  Atomistic simulations of the magnetic neutron scattering from nanoparticles: towards the understanding of complex spin structures beyond the super spin model

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. I will illustrate some of our simulation results for the magnetic SANS cross section of spherical nanoparticles with different types of surface anisotropy.