Current-induced displacements and precession of a Bloch wall in Ni-Fe thin films

Abstract

Rectangular or exponential current pulses of duration ≂0.1 μs traversing a Bloch wall are found to induce wall displacements Δx≤10 μm/pulse in a Ni81Fe19 film of thickness ≂263 nm. The critical current density for wall displacement is jc≂1.35×106 A/cm2, about 20–200 times lower than for Néel 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 jc value and easy precession of spins in a Bloch wall reflect the very small value ≂300 μT 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 jc. A dc easy-axis field smaller than Hc produces only a very slow decrease of jc.