Ga+ Ion Irradiation-Induced Tuning of Artificial Pinning Sites to Control Domain Wall Motion

Abstract

Domain-wall-based devices are considered one of the candidates for the next generation of storage memories and nanomagnetic logic devices due to their unique properties, such as nonvolatility, scalability, and low power consumption. Field or current-driven domain walls require a regular and controlled motion along the track in which they are stored in order to maintain the information integrity during operation. However, their dynamics can vary along the track due to film inhomogeneities, roughness of the edges, and thermal fluctuations. Consequently, the final position of the domain walls may be difficult to predict, making difficult the development of memory and logic applications. In this paper, we demonstrate how Ga+ ion irradiation can be used to locally modify the material properties of the Ta/CoFeB/MgO thin film, creating regions in which the domain wall can be trapped, namely motion barriers. The aim is to push the domain wall to overcome thin-film inhomogeneities effects, while stopping its motion at artificially defined positions corresponding to the irradiated regions. Increasing the driving force strength, the domain wall can escape, allowing the shifting between consecutive irradiated regions. In this way, the correct positioning of the domain walls after the motion is ensured. The study shows that the driving force strength, namely current density or magnetic field amplitude, needed to overcome the irradiated regions depends on the ion dose. These results show a reliable approach for domain wall manipulation, enabling a precise control of the domain wall position along a track with synchronous motion.