Anisotropic domain evolution in epitaxial Fe/GaAs(001) wires

The magnetization reversal in in-plane magnetized epitaxial Fe/GaAs(001) wire elements with dimensions of 15 μm (width $w)$×500 μm (length $l)$×300 Å (Thickness $t)$ has been studied by scanning Kerr microscopy and Kerr magnetometry. The two-jump switching process is observed which is characteristic for the magnetization reversal in continuous epitaxial Fe(001) films with fourfold in-plane anisotropy. However, in contrast to the continuous film, the domain nucleation and growth processes which mediate the irreversible magnetization jumps at the two critical fields, $H_{c1\mathrm{}}$ and $H_{c2\mathrm{}}$ are found to be determined by the orientation of the applied field with respect to the long and the short wire axis. This anisotropy in the domain evolution is a result of the combined effects of local edge dipolar fields, the fourfold magnetocrystalline anisotropy as well as the finite and anisotropic lateral extensions of the wires. Due to the large aspect ratio of $l/w,$ the boundaries of the long and short wire edges restrict the domain expansion differently. Consequently, this “shape” anisotropy in the domain evolution contrasts with the conventional shape anisotropy associated with macroscopic (average) demagnetization fields.