Size-Dependent Multi- to Single Domain Transition of UV Laser-Driven Ferromagnetic Co Nanoparticles Under External Magnetic Field

he magnetic domain of cobalt (Co) nanoparticles (NPs) was studied as a function of particle size. Various single crystalline and uniform Co NPs were prepared using a novel UV laser irradiation technique on ultra thin Co films under an external applied magnetic field. Structural and magnetic characteristics were analyzed with transmission electron microscopy and superconducting quantum interference devices. The experimental observations indicate that during Co NP growth, externally applied magnetic fields and size-dependent NP surface effects strongly facilitate multi-to-single domain transition at a critical diameter of about 10 nm, an extremely small NP size that is suitable for higher density storage applications.This work was supported by the IT R&D program of MKE/KEIT [10043398, Fundamental technology development of materials of magnet resistance change (MR ratio > 120%) and tunneling barrier for advanced low power memory device]