Domain wall propagation in modulated-diameter cylindrical nanowires is a key phenomenon to be studied with a view to designing three-dimensional magnetic memory devices. In this framework, we quantified theoretically the driving force needed for a domain wall to overcome the potential barrier related to modulated diameter geometry in order to jump from one stable position to another.
Electrochemical growth of cylindrical nanowires technique is continuously progressing, and is nearing compatibility with design of a three-dimensional race-track memory. The information stored in this type of solid-state device would be encoded by magnetic domains separated by magnetic domain walls. The control of the domain wall position may be achieved by introducing geometrical inhomogeneities during the fabrication process. Smaller cross-section reduces the internal domain wall energy and thus plays the role of the energy well which implies that some threshold driving force must be applied to overcome the barrier.
In this context, we proposed both a quantitative micromagnetic description of the domain wall behavior using our home-made finite element micromagnetic software, and a simplified analytical model which relates geometric parameters to the critical driving force needed to unpin the domain wall. Qualitative analytical model for gently sloping modulations resulted in a simple scaling law. We focused on the case of wall motion under the conservative driving force produced by a magnetic field applied along the wire’s axis. It shows that the domain wall depinning field value is mostly proportional to the modulation slope. Our approach is quite general and may be extended further to study the effect of other driving forces such as spin-polarized current in order to assist experimental system design.
Teams: THEORY/SIMULATIONS and SPIN TEXTURES
Funding: ANR JCJC MATEMAC-3D, FP7/2007-2013 M3d n°309589
Further reading: Modeling magnetic-field-induced domain wall propagation in modulated-diameter cylindrical nanowires, J. A. Fernandez-Roldan, A. De Riz, B. Trapp, C. Thirion, M. Vazquez, J.-C. Toussaint, O. Fruchart, D. Gusakova. Scientific Reports, 9, 5130 (2019). DOI: 10.1038/s41598-019-40794-1
Contact: Daria Gusakova
Figure: (a) Illustration of the domain wall based magnetic memory concept. (b) Illustration of the domain wall simulated in modulated-diameter cylindrical nanowire. (c) Topography and magnetic image of a NiCo alloy nanowire with three distinct segments of different diameter (from PhD thesis of B.Trapp).