Mechanisms for low-field, and multiple domain wall injection into magnetic nanowires.

The motion of a domain wall within a magnetic nanowire is important for the development of future recording, sensing and logic devices.~ The speed of a field driven domain wall is quickest when the applied magnetic field is below the so-called Walker Field which depends on the size and material properties of the wire.~ However, the field needed to inject a domain wall into a wire is much greater than the Walker Field which leads to slow wall motion because of the nucleation of vortices and anti-vortices, or fast motion with complicated domain wall structures. We present Landau-Lifshitz simulation results showing a significant decrease in the field needed to inject a domain wall into the wire for a variety of injection designs including: pads, rings, straight ends, and tapered ends.~ We also find that by applying a transverse field the required driving field to inject the wall decreases, and that the domain wall motion in the wire is faster.~ The magnetization of the pad and ring injection designs can be easily manipulated so that multiple walls with a known magnetization structure are injected allowing for faster, more reliable domain wall motion.