Size-dependent changeover in magnetization reversal mode of self-assembled one-dimensional chains of spherical Fe3O4 nanoparticles

Understanding the ferromagnetic behavior of coupled magnetic nanoparticles (NPs) in a chain structure, called a "nanochain (NC) , will open up new routes for its practical use. Here, we report the magnetization reversal modes in isolated magnetite (Fe3O4) NPs with diameters of 100 and 200 nm, as well as those of one-dimensional (1D) self-assembled NCs consisting of these NPs. NCs consisting of 100-nm diameter NPs switched through a transverse domain wall-like motion. Meanwhile, in 200-nm diameter NPs and NCs, we observed 3D magnetic vortex states that were more energetically favorable than single domain or multidomain states.