Current-driven domain wall mobility in polycrystalline Permalloy nanowires: A numerical study

Abstract

A complete understanding of domain wall motion in magnetic nanowires is required to enable future nanowire based spintronics devices to work reliably. The production process dictates that the samples are polycrystalline. In this contribution, we present a method to investigate the effects of material grains on domain wall motion using the GPU-based micromagnetic software package MuMax3. We use this method to study current-driven vortex domain wall motion in polycrystalline Permalloy nanowires and find that the influence of material grains is fourfold: an extrinsic pinning at low current densities, an increasing effective damping with disorder strength, shifts in the Walker breakdown current density, and the possibility of the vortex core to switch polarity at grain boundaries. V

Domain walls within domain walls in wide ferromagnetic strips

“…Possible origins for the symmetry breaking leading to incoherent precession of m DW in different parts of the DW could be edge effects, and/or quenched disorder, interacting with the DW [10,[14][15][16][17][18][19][20]; these may include dislocations, precipitates, grain boundaries, thickness fluctuations of the strip, etc. Here we explore the dynamics of extended DWs in wide CoPtCr PMA strips, with a Bloch wall equilibrium structure, using large-scale micromagnetic simulations with and without quenched disorder.…”

“…In order to account for the effect of quenched disorder, here assumed to originate from the polycrystalline structure of the strip [41], we construct grains using a Voronoi tessella- tion [14,15], with an average grain size of 11.9 nm [35]; see the inset of Fig. 2.…”

Micromagnetic modeling of domain wall motion in sub-100-nm-wide wires with individual and periodic edge defects

“…The damping parameter, α, described in Ref. 15, was set to 0.018, and the saturation magnetization M sat = 1.40 × 10 6 A/m. A uniaxial magnetocrystalline anisotropy of 4100 J/m 3 with random direction was present in each cell.…”

“…13 Micromagnetic simulations provide a tool to study the effect of edge roughness or anisotropy variations, subject to the limitations of the discretization cell size, which should be similar to the exchange length. LER can be introduced into a simulation by removing cells or blocks of cells from the edge of a nanowire in a model with cuboidal 14,15 or tetrahedral cells. 6 Other studies use a Voronoi cell geometry.…”

Coarsening dynamics of topological defects in thin permalloy films

“…We also investigate the effect of α on the relaxation process, using values ranging from the typical 0.01 for pure permalloy up to 0. magnetization dynamics of permalloy, they allow us to address the more general question of the effect of damping on the defect coarsening dynamics. Moreover, we also check the stability of our results with respect to adding quenched structural disorder to the system [27][28][29][30][31], by performing a Voronoi tessellation to divide the films into grains, mimicking the polycrystalline structure of the material [30,31]; we consider average grain sizes of 10, 20, and 40 nm. Disorder is then implemented by either setting a random saturation magnetization in each grain (from a normal distribution with mean M s and standard deviation of 0.1M s or 0.2M s ) [27,30], or decreasing the exchange coupling across the grain boundaries by 10%, 30%, or 50% [30,31].…”