Magnetic domain structure in nanocrystalline nickel electrodeposits

The correlation between the crystal/defect and the magnetic domain structure of nanocrystalline (nc) bulk nickel produced by electrodeposition was investigated. By means of conventional and high resolution transmission electron microscopy, an average grain size of 23 nm was determined; nano-grains surrounded by low angle and high angle boundaries and the presence of nanotwins and stacking faults were observed. The nc nickel exhibited soft magnetic properties. Lorentz TEM (LTEM) in the Fresnel mode revealed magnetic domains of various sizes in the micrometer range extending over many grains, with a few random pinning sites, exhibiting a magnetic ripple structure and vortices. The LTEM was used to investigate the motion of domain walls driven by an external in situ magnetic field and to determine the domain wall width. Domain wall movement was observed at very small magnetic fields along the hysteresis loop. The correlation of the grain size and magnetic properties shows good agreement with the Herzer random anisotropy model for nanocrystalline materials, although the nc nickel studied here has no traces of an amorphous phase