Rectangular current pulses of duration 0.14 μs, flowing across Bloch domain walls in Ni81Fe19 films, cause displacements Δx of these walls, observable by Kerr-contrast microscopy. In zero magnetic field, Δx reaches ≂14 μm/pulse at current densities ≂30% above the value jc where wall motion starts. This critical current density is jc≂1.2×1010 A/m2 for a film thickness w=263 nm. We have measured jc versus film thickness for w=120–740 nm, and find jc∝w−2.1. This suggests strongly that the observed wall motion is associated with an S-shaped distortion of the wall by the circumferential magnetic field of the current. This wall distortion is limited by the wall surface tension. The wall structure becomes that of the so-called asymmetric Néel wall. Through wall distortion, the current pulse pumps kinetic energy and momentum into the wall. This kinetic energy is then dissipated during ballistic wall motion happening largely after the end of the pulse. We also find jc to be independent of pulse duration.

Rectangular or exponential current pulses of duration 20.1 ys traversing a Bloch wall are found to induc.e wall displacements Ax<10 ,um/pulse in a NisiFer, film of thickness ~263 nm. The critical current density for wall displacement is j,, 1.35 X IO6 A/cm', about 20-200 times lower than for NCel or cross-tie walls investigated earlier. Wall motion arises probably from the precession of wall spins under the influence of the "s-d exchange torque" exerted by conduction electrons crossing the wall. The low j, value and easy precession of spins in a Bloch wall reflect the very small value 2 300 FT of the wall demagnetizing field which opposes spin orientation out of the wall plane in films of this thickness. A dc in-plane hard-axis field causes a linear decrease of j,. A dc easy-axis fleld smaller than H, produces only a very slow decrease of j,

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