Exchange forces between domain wall and electric current in permalloy films of variable thickness

Abstract

Wall displacements are induced by large current pulses crossing a wall, in Ni81Fe19 films. In films of thickness w<35 nm containing Néel walls, the sense of wall motion is found to be independent of the magnetization sense in the two domains adjacent to the wall, and is identical to the sense of motion of the electronlike charge carriers. This shows that the wall motion is not caused by stray magnetic fields, but rather by s-d exchange forces generated by conduction electrons. The value ≂5×107 A cm−2 of the needed current density agrees with predictions of a theory based on s-d exchange. In the case of cross-tie walls in films with 35 nm <w<86 nm, the sense of wall motion does depend on the sense of the domain magnetizations. The force of the circumferential magnetic field of the current is probably important, here.

Spin-polarised currents and magnetic domain walls

“…Vernier et al were able to estimate the pressure applied to the wall per unit current density as about 0.44 nN/A, of the same order of magnitude as the values (0.6 nN/A) that can be derived from the early experiments of Berger and colleagues [410,412]. The measurement of the current induced wall velocity was accomplished by Yamaguchi et al using a bent L-shaped wire geometry with an injection pad, with the detection of individual walls by carried out by MFM [444].…”

“…After a quantitative analysis of the domain wall motion the coupling constant of the drift velocity (∝ the current density) and the force on the wall was measured, and found to be of the same order of magnitude as predicted by the theory [411]. In an extension of this experiment, Hung and Berger measured the differing effects of high current density pulses on Néel and cross-tie walls in thin permalloy films [412]. Experimental efforts to research these topics then disappeared for many years before the discovery of current driven switching effects in multilayer point contacts [413] and nanopillars [414] by the group of Buhrman at Cornell.…”

Pulsed-current-induced domain wall propagation in Permalloy patterns observed using magnetic force microscope

“…Unlike the domain drag, the exchange force is independent of the sample thickness. The third mechanism is caused by the "global field" [10]. The electric current through the sample produces a circumferential magnetic field, which runs in closed loops perpendicular to the direction of current.…”

Theory of Domain Wall Dynamics under Current

“…5 In 1984, 10,11 he studied the effect of the force arising from the reflection of conduction electron by domain wall caused by this exchange coupling. This force was associated with a wall mobility introduced phenomenologically.…”