INVESTIGATION OF MICROMAGNETISM AND MAGNETIC REVERSAL OF NI NANOPARTICLES USING A MAGNETIC FORCE MICROSCOPE

Isolated Ni nanoparticles were studied in situ by atomic and magnetic force microscopy in the presence of an additional external field up to 300 Oe. By comparing topographic and magnetic images, and also by com puter modeling of magnetic images, it was established that particles s maller than 100 nm are single-domain and easily undergo magnetic rever sal in the direction of the applied external magnetic field. For large magnetic particles, the external magnetic field enhances the magnetiz ation uniformity and the direction of total magnetization of these par ticles is determined by their shape anisotropy. Characteristics of the magnetic images and magnetic reversal of particles larger than 150 nm are attributed to the formation of a vortex magnetization structure i n these particles. (C) 1998 American Institute of Physics.