Nucleation of Ferromagnetic Domains in Iron Whiskers

Nucleation fields up to 483 oe have been experimentally observed for the reversal of magnetization in regions of nearly perfect iron whiskers about 5 μ thick. This is near the theoretical limit ${\text{2K}}_1{\mathrm{/M}}_s\text{\hspace{0.17em}(\hspace{0.17em}=\hspace{0.17em}560\hspace{0.17em}}\mathrm{oe}\hspace{0.17em}\mathrm{for}\hspace{0.17em}\mathrm{iron})$ for the coercive force resulting from magnetocrystalline anisotropy. In addition, conspicuous growth defects on the surface are observed to be sites of easy nucleation. A field of about one oersted, if applied to the damaged end of an iron whisker of this size, suffices to reverse the magnetization by domain wall motion.