Critical parameters for current-induced domain wall motion

Permalloy ring structures with nonmagnetic contacts have been fabricated for transport measurements. The position of a domain wall is determined by low-temperature measurements of the resistance between different pairs of contacts. By monitoring the resistance, the threshold current density at which the current moves the domain wall is determined. Injecting a single 20 μs pulse with a current density of 3×10¹² A/m into a 200 nm wide and 27 nm thick line moves the domain wall by 20 μm, with an effective velocity of 1 m/s. It is found that the domain wall velocity is largely independent of the pulse duration but varies between 0.2 m/s and 1.3 m/s with the wire dimensions. Also, the velocity is shown to increase with current density. In addition, the threshold current density and velocity are determined to be dependent on the geometry of the structure and on the resulting domain wall type. Theoretical predictions reveal that the velocity is dependent on material parameters but not on the geometry of the structure. This implies that the simple one-dimensional model of a domain wall used in current calculations in this work is not sufficient to explain the observations.