Electronic phenomena studied in the nordic countries

The collective state of densely packed magnetic nanoparticles

Not scheduled

15m

Max IV Lund

Speaker

Mr Mikael S. Andersson (Uppsala University)

Description

We will present results on densely packed maghemite ($\gamma$-Fe$_2$O$_3$) nanoparticles forming a superspin glass state. A superspin glass is a nanoparticle analogy to the atomic spin glass state, much like a superparamagnet is an analogy to a paramagnet. The main experimental technique used to obtain the results was SQUID magnetometry. The results that we present show that the magnetic properties of the superspin glass state is in most regards the same as the corresponding properties in an atomic spin glass. These results include measurements of non-equilibrium phenomena such as ageing, memory and rejuvenation. We will also present results highlighting some of the differences that exist, e.g. the individual relaxation time of building blocks, which for atomic spin glasses is fixed while temperature dependent for superspin glasses. Lastly we will discuss how size and size distribution of the nanoparticle building blocks impacts the collective properties of the superspin glass.