Nucleation, imaging, and motion of magnetic domain walls in cylindrical nanowires

Abstract

We report several procedures for the robust nucleation of magnetic domain walls in cylindrical permalloy nanowires. Specific features of the magnetic force microscopy contrast of such soft wires are discussed, with a view to avoid the misinterpretation of the magnetization states. The domain walls could be moved under quasistatic magnetic fields in the range 0.1−10 mT.

Fast Domain Wall Motion Governed by Topology and Œrsted Fields in Cylindrical Magnetic Nanowires

“…2d), corresponding to an average velocity of ≈ 350 m/s. However, the right hand DW remains pinned, highlighting a common and key issue for inferring DW velocities from motion distances: pinning on geometrical or microstructural defects hampers DW motion [33]. Depinning not only requires a current density above a critical value j dp , but re-pinning can also occur at another location with a deeper energy well, while the current pulse is still being applied.…”

Domain wall pinning in a circular cross-section wire with modulated diameter

“…Magnetization tends to be rather uniform over distances smaller than l ex , while it may rotate at larger scales under the influence of boundary conditions or dipolar energy. In cylindrical nanowires, depending on the wire diameter so far two different domain wall types have been theoretically predicted [33,31] and experimentally observed [44,23,21,42]. Moderate wire diameters (D < 7l ex ) considered in this chapter favor the formation of the socalled transverse-like domain wall [28,47].…”

Magnetic Nanowires and Nanotubes

“…Walls have been imaged by several groups and various microscopy techniques. Experimentally, the increase of wall width with wire diameter is clear (Da Col et al 2016), although it has not been studied quantitatively in a systematic manner. In tubes, analytical modelling predicts that the width of TVWs steadily decreases for increasing β, while the width of BPWs reaches a maximum for a given β (López-López et al 2012).…”

“…Specific strategies need to be deployed in the case of wires and tubes. Using the natural bending of very thin wires at surface is efficient to mimick bends in flat strips (Da Col et al 2016), however the process is poorly controlled. Another way is to use modulations of diameter to create potential barriers with a view to keep the wall in a given area (Bochmann et al 2018).…”

“…Another way is to use modulations of diameter to create potential barriers with a view to keep the wall in a given area (Bochmann et al 2018). Yet another way is to proceed to demagnetization with a magnetic field applied transverse to the wire/tube axis (Biziere et al 2013, Da Col et al 2014, Da Col et al 2016, Bran et al 2016b, which seems to be the most efficient method. To the contrary, it seems that domain walls nucleate spontaneously towards remanence, whatever the direction of previous saturation, in the case of tubes with azimuthal magnetization (Staňo et al 2017b).…”