Nanoscale SEMPA measurements of trapped domain walls in thin film NiFe constrictions.


W. Casey Uhlig  and John Unguris

Electron Physics Group, National Institute of Standards and Technology, Gaithersburg, MD, 20899-8412, USA.


In recent years “nanotechnology” has established itself as a world-renowned buzzword humming through the ranks of the scientific arena.  The 4,000-year-old discovery of magnetism has also found itself enmeshed in the unfolding drama and has been coined “nanomagnetism.”  One component of this leading edge research investigates an effect known as spin-transfer torque (STT). Spin angular momentum from electrons in a spin-polarized current, at sufficient current densities (~ 108 A/cm2), can reverse the magnetization of a ferromagnetic element or manipulate the position of a trapped domain wall.

We used scanning electron microscopy with polarization analysis (SEMPA) to image the magnetic nanostructure of domain walls trapped in patterned NiFe thin film nanoconstrictions. Currents were applied to the structures to induce spin torque driven motion of the domain wall in the nanoconstriction. Various film geometries were investigated in order to understand how the size and shape of the constriction affects the magnetic nanostructure of the domain wall. The structures were fabricated using electron beam lithography. Constriction widths varied from 40 nm to 200 nm. The non-invasive nature of SEMPA allowed successful imaging of the unperturbed, remanent state of the trapped domain walls.  In 10 nm thick NiFe films, all of the observed trapped walls (within the constriction) were of the transverse type, and the domain wall widths were strongly dependent on both the width of the constriction (approximately equal to the width) as well as the shape of the constriction. Because SEMPA directly measures the magnetization direction, the image data allows meaningful quantitative comparisons to micromagnetic calculations. Simulations with inserted domain walls show good agreement with the behavior of the domain walls observed by SEMPA (see Figure 1). Detailed comparisons will be presented. 




Postdoc: W. Casey Uhlig

Mentor: John Unguris

Electron and Optical Physics Division (841)

Physics Laboratory

Bldg 216 , Room A233

Mail Stop 8412

Phone: 301-975-8269

Fax: 301-926-2746


Sigma Xi member: no

Poster Category: Physics