Magnetic Structure of Sculpted Nanospirals

Direct visualization of magnetic structures gives researchers a window into new possibilities at the Nanoscale.

Color map (left) reconstructed image showing the direction of magnetization and the stray magnetic fields in and around a cobalt nanospiral (color wheel indicates magnetization direction) that is only 20 nm in diameter (images taken using high resolution Lorentz microscopy), and (right) tomographic reconstruction showing the 3D shape of the nano-spiral. — Image courtesy of Argonne National Laboratory

The Science

The magnetic domains and interactions between three-dimensional (3D) sculpted nanostructures are directly visualized using a high-resolution transmission electron microscope specially designed for imaging magnetic materials.

The Impact

3D nanostructures are critical building blocks for complex mesoscopic systems and are therefore of significant technological importance. This research paves a path towards a clearer fundamental understanding of interactions between magnetic nanoscale building blocks, thereby enabling control of the properties of the mesoscopic system, and will contribute to their use in new technological applications in photonics and optics.

Summary

Confined magnetic nanostructures can exhibit novel behavior that emerges from interactions at the atomic and electronic scales. To achieve successful control over such phenomena, it is critical to understand the energetics of these systems in three dimensions. Research led by Argonne National Laboratory has succeeded in direct visualization of the magnetic structure in individual, sculpted 3D cobalt nanospirals with a wire diameter of 20 nm, using aberration-corrected Lorentz transmission electron microscopy (TEM). These results, combined with modeling, were used to analyze the magnetic interactions occurring at the nanoscale. Correlation with 3D tomography and high resolution TEM showed that the magnetic structure of these nanospirals is controlled by the shape anisotropy energy (i.e., the shape of the nanostructure dictates the preferential direction of magnetization), dominating over the magnetocrystalline anisotropy (i.e., the atomic structure of a nanospirals introduces preferential directions for the magnetization). Thin ﬁlms consisting of arrays of such sculpted nanostructures are potential candidates for a large variety of applications in the ﬁelds of photonics and optics as polarization ﬁlters, and as tissue scaffolds in biomedical applications. This research paves a path towards a clearer fundamental understanding of interactions between nanoscale building blocks, thereby enabling control of the properties of the mesoscopic system of which they form a part.

Contact

Amanda Petford-Long
Argonne National Laboratory
petford.long@anl.gov

Funding

DOE Office of Science, Basic Energy Sciences program (Lorentz TEM, 3D tomography, analysis of magnetic domains and interactions). Fabrication of the nanospirals was supported by the National Science Foundation; Image processing of the 3D date was supported by Air Force Office of Scientific Research.

Publications

C. Phatak, Y. Liu, E. B. Gulsoy, D. Schmidt, E. Schubert, A. Petford-Long, Visualization of the Magnetic Structure of Sculpted Three-Dimensional Cobalt Nanospirals” Nano Letters, 14, 759 (2014). [DOI: 10.1021/nl404071u]