Engineering topics

Im, M -Y

Publications and source records attributed to Im, M -Y.

3 records

DOE OSTI2011

X-ray imaging of vortex cores in confined magnetic structures

Cores of magnetic vortices in micron-sized NiFe disk structures, with thicknesses between 150 and 50 nm, were imaged and analyzed by high-resolution magnetic soft x-ray microscopy. A decrease of the vortex-core radius was observed from approximately 38 to 18 nm with decreasing disk thickness. By comparing with full three-dimensional micromagnetic simulations showing the well-known barrel structure, we obtained excellent agreement, taking into account instrumental broadening and a small perpendicular anisotropy. The proven magnetic spatial resolution of better than 25 nm was sufficient to identify a negative dip close to the vortex core, originating from stray fields of the core. Magnetic vortex structures can serve as test objects for evaluating sensitivity and spatial resolution of advanced magnetic microscopy techniques.

36 MATERIALS SCIENCE↗

DOE OSTI2010

Focused ion beam patterned Fe thin films A study by selective area Stokes polarimetry and soft x-Ray microscopy

We demonstrate the potential to modify the magnetic behavior and structural properties of ferromagnetic thin films using focused ion beam 'direct-write' lithography. Patterns inspired by the split-ring resonators often used as components in meta-materials were defined upon 15 nm Fe films using a 30 keV Ga{sup +} focused ion beam at a dose of 2 x 10{sup 16} ions cm{sup -2}. Structural, chemical and magnetic changes to the Fe were studied using transmission soft X-ray microscopy at the ALS, Berkeley CA. X-ray absorption spectra showed a 23% reduction in the thickness of the film in the Ga irradiated areas, but no chemical change to the Fe was evident. X-ray images of the magnetic reversal process show domain wall pinning around the implanted areas, resulting in an overall increase in the coercivity of the film. Transmission electron microscopy showed significant grain growth in the implanted regions.

36 MATERIALS SCIENCE↗

DOE OSTI2010

Switchable cell trapping using superparamagnetic beads

Ni{sub 81}Fe{sub 19} microwires are investigated as the basis of a switchable template for positioning magnetically-labeled neural Schwann cells. Magnetic transmission X-ray microscopy and micromagnetic modeling show that magnetic domain walls can be created or removed in zigzagged structures by an applied magnetic field. Schwann cells containing superparamagnetic beads are trapped by the field emanating from the domain walls. The design allows Schwann cells to be organized on a surface to form a connected network and then released from the surface if required. As aligned Schwann cells can guide nerve regeneration, this technique is of value for developing glial-neuronal co-culture models in the future treatment of peripheral nerve injuries.

36 MATERIALS SCIENCE↗