Reprint of: Out-of-equilibrium dynamics in superspin glass state of strongly interacting magnetic nanoparticle assemblies

Interacting magnetic nanoparticles display a wide variety of magnetic behaviors ranging from modified superparamagnetism, superspin glass to possibly, superferromagnetism. The superspin glass state is described by its slow and out-of-equilibrium magnetic behaviors akin to those found in atomic spin glasses. In this article, recent experimental findings on superspin correlation length growth and the violation of the fluctuation-dissipation theorem obtained in concentrated frozen ferrofluids are presented to illustrate certain out-of-equilibrium dynamics behavior in superspin glasses. - Highlights: • Recent experimental findings on superspin glass dynamics in magnetic nanoparticle systems. • Advantages of magnetic nanoparticles for the study of spin glass physics. • Open questions and future directions in superspin glass research