Seminarium om kondenserade materiens fysik - Lasse Larson

Lasse Larson: Depinning transition and Barkhausen avalanches of thin film domain walls with internal degrees of freedom

Abstract

The jerky dynamics of domain walls driven by applied magnetic fields in disordered ferromagnets—the Barkhausen effect—is a paradigmatic example of avalanches or crackling noise. I’ll start by discussing our recent study of Barkhausen noise in disordered Pt/Co/Pt thin films with perpendicular magnetic anisotropy due to precessional motion of domain walls using full micromagnetic simulations, allowing for a detailed description of the domain wall internal structure consisting of topological defects known as Bloch lines [1]. The scaling features of the Barkhausen jumps appear to agree with those of the quenched Edwards-Wilkinson (qEW) equation, but since the reachable domain wall lengths in micromagnetic simulations are limited to a few micrometers, this result could be affected by finite-size effects. To overcome such limitations, I’ll discuss our very recently developed collective coordinate model of thin film domain walls able to account for the internal degrees of freedom of the domain wall while allowing us to reach much larger system sizes. The model exhibits a depinning phase transition transition with disorder-dependent scaling: For weak disorder, excitations of the internal magnetization are rare, and the depinning transition takes on exponent values of the quenched Edwards-Wilkinson equation. Stronger disorder results in disorder-dependent exponents concurrently with nucleation of an increasing density of Bloch lines within the domain wall [2].  

[1] T. Herranen and L. Laurson, Phys. Rev. Lett. 122, 117205 (2019). 

[2] A. Skaugen and L. Laurson, Phys. Rev. Lett. 128, 097202 (2022).

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Seminarium om kondenserade materiens fysik