  Ferromagnetic electrodes of a lateral semiconductor-based spin-valve
structure are designed to provide a maximum of spin-polarized injection
current. A single-domain state in remanence is a prerequisite obtained by
nanostructuring Permalloy thin film electrodes. Three regimes of aspect ratios
$m$ are identified by room temperature magnetic force microscopy: (i)
high-aspect ratios of $m \ge 20$ provide the favored remanent single-domain
magnetization states, (ii) medium-aspect ratios $m \sim 3$ to $m \sim 20$ yield
highly remanent states with closure domains and (iii) low-aspect ratios of $m
\le 3$ lead to multi-domain structures. Lateral kinks, introduced to bridge the
gap between micro- and macroscale, disturb the uniform magnetization of
electrodes with high- and medium-aspect ratios. However, vertical flanks help
to maintain a uniformly magnetized state at the ferromagnet-semiconcuctor
contact by domain wall pinning.
