The role of non-collinear spins on the magnetic properties of uncoupled nanometer-size particles

A study of the magnetic properties of an assembly of non-interacting iron oxide-based nano-particles is presented. The measured average particle size is found to approach the expected thickness of the spin disordered layer. In this regime, the magnetization is characterized by two parameters: Tb above which the particle acts as a single domain, and TE below which intra-particle coupling between pinned and unpinned spins become important.