Supermagnetism

TLDR

Supermagnetism encompasses regimes from weakly interacting superparamagnetic nanoparticles to strongly interacting ensembles that exhibit superspin glass and superferromagnetic behavior. This review aims to highlight the most important developments in supermagnetism across its three main subfields. The authors synthesize recent progress by surveying advances in superparamagnetism, superspin glass, and superferromagnetism.

Abstract

An ensemble of nanoparticles in which the inter-particle magnetic interactions are sufficiently weak shows superparamagnetic behaviour as described by the Néel–Brown model. On the contrary, when inter-particle interactions are non-negligible, the system eventually shows collective behaviour, which overcomes the individual anisotropy properties of the particles. At sufficiently strong interactions a magnetic nanoparticle ensemble can show superspin glass (SSG) properties similar to those of atomic spin glass systems in bulk. With a further increase in concentration, but still below physical percolation, sufficiently strong interactions can be experienced to form a superferromagnetic (SFM) state. SFM domains in a non-percolated nanoparticle assembly are expected to be similar to conventional ferromagnetic domains in a continuous film, with the decisive difference that the atomic spins are replaced by the superspins of the single-domain nanoparticles. In this review we highlight the most important developments in the field of supermagnetism, which comprises three fascinating subjects: superparamagnetism, SSG and superferromagnetism.