Electron transport limited by the rotating exchange potential of domain wal
ls is calculated in the ballistic limit for the itinerant ferromagnets Fe,
Co, and Ni. When realistic band structures are used, the domain-wall magnet
oresistance is enhanced by orders of magnitude compared to the results for
previously studied two-band models. Increasing the pitch of a domain wall b
y confinement in a nanostructured point contact is predicted to give rise t
o a strongly enhanced magnetoresistance. [S0163-1829(99)02302-4].