The behaviour of domains and domain walls (DWs) in magnetic nanostructures has led to many developments in our understanding of fundamental magnetisation reversal processes. Interactions between DWs and geometrical structural features are one area of interest where previous studies largely consider the quasi-static field driven behaviour of DWs based on a structure in an energetically minimised state[1]. In this regime the behaviour of DWs can be described by properties such as their type, chirality and topology[2,3].

More recently, an increasing interest in DW dynamics has developed due to the potential for novel spintronic devices and the desire for high operating speeds. In this dynamic regime, gyroscopic precession limited and time-dependent changes in micromagnetic structure become significant in addition to the minimised energy states which dominate in the quasi-static regime. The micromagnetic structure of propagating DWs become distorted, and with driving fields in excess of the Walker field periodic transformations in DW type and chirality take place[4].

In this work both experimental focussed MOKE measurements and micromagnetic simulations are used to explore the behaviour of a dynamically propagating DW arriving at a Y-shaped vertex between three nanowires with a 120 degree opening. The DW either propagates through one of the nanowire paths or becomes pinned at the vertex, the outcome being determined by the DW structure at the point of arrival at the vertex. Thus, the final magnetisation state strongly depends on Walker breakdown processes associated with the incoming DW dynamics.

This work builds on our understanding magnetisation reversal processes in artificial spin ice structures comprising of many nanowire vertices. In addition this work also has implications for the development of novel DW based spintronic devices.

[1] D.M. Burn et.al. Phys. Rev. B. 88, 104422 (2013)
[2] K. Zeissler et.al. Sci. Rep., 3, 1252 (2013)
[3] A. Pushp, et.al. (2013). Nat. Phys., 9, 505. (2013)
[4] G.S.D. Beach, et.al. Nat. Mater., 4, 741. (2005)