Deroughening of a 1D Domain Wall in an Ultrathin Magnetic Film by a Correlated Defect

Interaction of a field-driven magnetic domain wall with a correlated (line) defect is examined by Kerr imaging in subnanometer thin Co films. The line defect directs and confines the wall near the bottom of the effective potential trough $U_{\mathrm{eff}}$, which competes with underlying random disorder that roughens the wall. We observe a kinetic “deroughening” with roughness exponent $\zeta \sim 0.1$ well below $\zeta =2/3\mathrm{}$ characteristic of random defects. Deroughening occurs on lengths greater than an inherent elastic screening length $L_{\mathrm{el}}$, which is consistently explained by the restoring action of $U_{\mathrm{eff}}$.