Barkhausen noise from domain walls with internal degrees of freedom

Abstract

Domain walls in disordered ferromagnets—interfaces separating oppositely magnetized regions—are commonly modeled as elastic interfaces in random media. However, real domain walls possess internal degrees of freedom related to the local magnetization direction at the wall's midpoint, which are not captured by simple elastic interface models. Here, we investigate how these internal degrees of freedom influence Barkhausen noise arising from the jerky field-driven motion of linelike domain walls in disordered thin ferromagnetic films with strong perpendicular magnetic anisotropy. Using a recently developed reduced model that incorporates internal wall dynamics, we simulate systems two orders of magnitude larger than those accessible via full micromagnetic simulations. We focus on Bloch line dynamics and identify a disorder-driven mechanism where Bloch lines accumulate near the edges of moving wall segments during avalanches, thereby impeding further propagation. This mechanism leads to distinctive statistical features in Barkhausen avalanches, including pronounced bumps in the cutoffs of the avalanche distributions, skewness of the average avalanche shape evolving with the avalanche duration, and reduced domain wall roughness at large scales.