Abstract
Finite temperature micromagnetic simulations were used to investigate the magnetisation structure, propagation dynamics and stochastic pinning of domain walls in rare earth-doped Ni80Fe20 nanowires. We first show how the increase of the Gilbert damping, caused by the inclusion rare-earth dopants such as holmium, acts to suppress Walker breakdown phenomena. This allows domain walls to maintain consistent magnetisation structures during propagation. We then employ finite temperature simulations to probe how this affects the stochastic pinning of domain walls at notch-shaped artificial defect sites. Our results indicate that the addition of even a few percent of holmium allows domain walls to pin with consistent and well-defined magnetisation configurations, thus suppressing dynamically-induced stochastic pinning/depinning phenomena. Together, these results demonstrate a powerful, materials science-based solution to the problems of stochastic domain wall pinning in soft ferromagnetic nanowires.
Highlights
One clear route to enhancing the reliability, and feasibility, of DW devices is to directly supress the Walker breakdown (WB) phenomena that lie at the heart of stochastic behaviour
We have used room temperature micromagnetic simulations to show that doping Ni80Fe20 nanowires with small amounts (
Such doping causes increases in the damping factor, α, which pushes the onset of Walker breakdown phenomena beyond typical propagation fields, preventing the complex DW dynamics that lie at the heart of stochastic DW pinning
Summary
Finite temperature micromagnetic simulations were used to investigate the magnetisation structure, propagation dynamics and stochastic pinning of domain walls in rare earth-doped Ni80Fe20 nanowires. We first show how the increase of the Gilbert damping, caused by the inclusion rare-earth dopants such as holmium, acts to suppress Walker breakdown phenomena This allows domain walls to maintain consistent magnetisation structures during propagation. A number of methods of suppressing WB have been previously proposed including the patterning of controlled nanowire edge profiles[13,14], applying transverse magnetic fields[15], inducing perpendicular magnetic anisotropies[16], or increasing the Gilbert damping parameters, α, of the materials from which the nanowires are formed[17] For the latter, increased values of α in soft materials such as Ni80Fe20 can be obtained by doping with a few percent of rare earth (RE) metals such as terbium or holmium[18,19] which increase the strength of spin-orbit interactions and the rate at which energy is dissipated by precessing spins[17,18]. This could be applied to create devices where DW behaviour is intrinsically well-defined
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