Asymmetrical energy landscape for domain wall motion induced by compositional gradients in ferromagnetic nanowires*

In recent years, 3D magnetic systems and curvilinear nanostructures have appeared as exciting alternatives for developing novel spintronics applications based on domain wall motion. In particular, complex and interesting spin textures and novel physics phenomena can be observed in cylindrical nanowires. Electrodeposition is a versatile tool for the synthesis of cylindrical nanowires with controlled morphology and composition. Recent works have shown that introducing local changes in composition along the axial direction in permalloy nanowires is very efficient for controlling the magnetisation dynamics. 

We will show in this work that electrochemical deposition also allows the introduction of gradual changes in the Fe/Ni ratio along the axis of the nanowires. This introduces a gradual change of the ferromagnetic properties, producing an asymmetrical energy landscape for the magnetic domain walls along the nanowire, as shown by micromagnetic simulations. In addition, these compositional gradients produce an asymmetrical landscape for domain wall motion, which is reflected in asymmetrical magnetisation processes under an applied magnetic field, paving the way towards full control of the movement of domain walls along these nanowires.