Creep turns linear in narrow ferromagnetic nanostrips.

Jonathan Leliaert,Ben Van de Wiele,Luc Dupré,Gianfranco Durin,Lasse Laurson,Arne Vansteenkiste,Bartel Van Waeyenberge

doi:10.1038/srep20472

Abstract

The motion of domain walls in magnetic materials is a typical example of a creep process, usually characterised by a stretched exponential velocity-force relation. By performing large-scale micromagnetic simulations, and analyzing an extended 1D model which takes the effects of finite temperatures and material defects into account, we show that this creep scaling law breaks down in sufficiently narrow ferromagnetic strips. Our analysis of current-driven transverse domain wall motion in disordered Permalloy nanostrips reveals instead a creep regime with a linear dependence of the domain wall velocity on the applied field or current density. This originates from the essentially point-like nature of domain walls moving in narrow, line- like disordered nanostrips. An analogous linear relation is found also by analyzing existing experimental data on field-driven domain wall motion in perpendicularly magnetised media.

Highlights

The motion of domain walls in magnetic materials is a typical example of a creep process, usually characterised by a stretched exponential velocity-force relation
In ref. 15, Kim et al experimentally evidenced that in perpendicular magnetic anisotropy (PMA) materials the creep scaling law, Eq (1) breaks down when the geometries confining the domain walls (DWs) are reduced in dimension: in the Ta/Pt/Co90Fe10/Pt nanostrips, narrower than 300 nm, DWs could no longer be described as rough elastic lines, as assumed in the derivation of Eq (1); rather, they behaved like compact objects jumping across energy barriers resulting in a creep motion strongly deviating from Eq (1)
We have shown that the velocity of compact DWs displays a simple linear dependence on the driving force

Summary

Results and Discussion

This is in sharp contrast with the narrow nanostrip where v linearly depends on the applied field for low fields, in agreement with Eq (16) This provides experimental evidence for the existence of the linear creep regime at small driving forces in case of compact DWs, behaving like point particles in a one-dimensional random potential. This mainly originates from the small DW widths in PMA materials, resulting in significantly stronger pinning than in Permalloy nanostrips[51].

Conclusion

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Author Contributions

Additional Information