Linear-chain assemblies of iron oxide nanoparticles

•Hydrothermal synthesis of pure phase 200nm Fe3O4 nanoparticles.•Studies of linear-chain assemblies of iron oxide nanosphere by FESEM.•Micromagnetic simulations showed the presence of 3D vortex states.•The B.E. for different numbers of particles in linear chain assemblies were calculated. We synthesized iron oxide nanoparticles using a simple hydrothermal approach and found several types of segments of their linear-chain self-assemblies as observed by field emission scanning electron microscopy. X-ray diffraction and transmission electron microscopy measurements confirm a well-defined single-phase FCC structure. Vibrating sample magnetometry measurements exhibit a ferromagnetic behavior. Micromagnetic numerical simulations show magnetic vortex states in the nanosphere model. Also, calculations of binding energies for different numbers of particles in the linear-chain assemblies explain a possible mechanism responsible for the self-assemblies of segments of the linear chains of nanoparticles. This work offers a step towards linear-chain self-assemblies of iron oxide nanoparticles and the effect of magnetic vortex states in individual nanoparticles on their binding energy.