Abstract
We study the physical origins of stochastic domain wall pinning in soft ferromagnetic nanowires using focused magneto-optic Kerr effect measurements and dynamic micromagnetic simulations. Our results illustrate the ubiquitous nature of these effects in Ni80Fe20 nanowires, and show that they are not only a result of the magnetisation history of the system (i.e. the magnetisation structure of the injected domain walls), and the onset of non-linear propagation dynamics above the Walker breakdown field, but also a complex interplay between the two. We show that this means that, while micromagnetics can be used to make qualitative predictions of the behaviour of domain walls at defect sites, making quantitative predictions is much more challenging. Together, our results reinforce the view that even in these simple pseudo-one dimensional nanomagnets, domain walls must be considered as complex, dynamically evolving objects rather than simple quasi-particles.
Highlights
The behaviour of domain walls (DWs) in soft ferromagnetic nanowires [1] has been a topic of intense research since proposals for using DWs to represent data in non-volatile and solid state logic [2, 3] and memory [4, 5] devices were made around the turn of the century
In the previous section we presented experimental results that illustrated the ubiquitous nature of stochastic DW pinning in soft ferromagnetic nanowires, and demonstrated why these effects cannot be caused purely by DWs being injected with poorly defined chiralities
While it is impossible to directly correlate the simulated dynamics with those occurring in the experimentally characterised nanowires, we propose that the enhanced stochasticity observed for DWs injected from nucleation pads may result from similar effects: For example, different modes of injection from the nucleation pads may lead to substantially different DW
Summary
The behaviour of domain walls (DWs) in soft ferromagnetic nanowires [1] has been a topic of intense research since proposals for using DWs to represent data in non-volatile and solid state logic [2, 3] and memory [4, 5] devices were made around the turn of the century. For example in the experimental measurements presented in figures 1 and 2, DWs were introduced into the nanowires from extended nucleation pads with relatively broad IFDs. It was interesting to examine whether the stochasticity of DW pinning/depinning could be reduced if more controlled methods of DW injection were used.
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