Colloquium: Dr. Johan van Lierop
Arrested Dynamics: Cooperative Phenomena in and amongst Nanoparticles
The physics of the magnetism from nanoparticles has been a topic of significant research interest to a wide variety of disciplines in recent years. Difficulties in translation to application arise from the particle's surface magnetism dominating the field response. In general, the physics of the surface magnetism is understood poorly. We study the cooperative phenomena that occur at the nanoscale at the surface and interface between a transition metaloxide nanoparticle and its transition metal or metaloxide shell as model systems. I
will present our investigations of the overall, elemental and atomic magnetism that reveals the novel interfacial magnetism in core/shell nanoparticles, and new ways to control and recapture lost moments. Building on our understanding of nanoparticle magnetism, I will tell you about our pioneering studies of cooperative phenomena from interactions between single domain nanoparticles. The nature of cooperative phenomena driving magnetic order in a crystal with only interacting dipoles has been explored theoretically since the 1940's, and Monte Carlo work in the 1980's raised the possibility of a new class of ferromagnetic materials composed of crystalline arrangements of nanoparticles. We have identified intriguing magnetism from macroscopic 3D crystals made of nanoparticles, and unconventional magnetism from functional nanoparticle assemblies.