Selective injection of magnetic domain walls in Permalloy nanostripes

Abstract

This work explores the conditions that allow the injection and pinning of different magnetic domain walls (DWs) in Permalloy nanostripes with notches of different shapes. The injection is done under a constant external field by applying a 10 ns current pulse through an adjacent current line. The type of DW is identified by its anisotropic magnetoresistance (AMR). We find that, while a quasi-static pinning (nucleating at zero field and propagating the DW to the notch by slowly increasing the external field) would allow to distinguish different types of DWs pinned at the notch, a dynamic pinning (nucleating, propagating, and pinning the DW under a constant non-zero magnetic field) makes the discrimination of different DWs very difficult. Micromagnetic simulations indicate that the AMR of the different types of DWs become quite similar to each other as the injection field increases. This might explain why at large injection fields, usually only one or two values of resistance are detected, depending on the shape of the notch. Therefore, caution should be taken when establishing a one-to-one relationship between a type of DW and a value of resistance, especially if the injection is done under a non-zero external magnetic field.