Jul 6, 2012
Planar nanowires grown on step-bunched templates exhibit room temperature ferromagnetic behaviour
Forming planar nanowire (NW) arrays that are ferromagnetic (FM) at room temperature (RT) using self-assembly techniques is a challenging task. Generally, self-assembly can only be achieved with very specific combinations of NW and substrate materials. Commonly used methods for producing planar nanostructures are step-flow growth and step-decoration methods. However, due to their small thickness these nanostructures are usually superparamagnetic. One option is to use shallow angle deposition on faceted surfaces to produce structures that are thick enough to overcome the superparamagnetism at RT.
Reporting their results in the journal Nanotechnology, S K Arora and colleagues have fabricated planar NW arrays of Co on oxidized step-bunched vicinal Si templates using a shallow angle deposition technique named ATLAS (atomic terrace low angle shadowing). The method allows the team to tailor the width and inter-wire separation of the nanowires by selecting the appropriate combination of deposition angle, flux direction and template periodicity. This opens up a wide range of possibilities to investigate the magnetic interactions, magnetization dynamics and spin transport at the nanoscale.
In the study, the team from Trinity College Dublin in collaboration with researchers from the Catalan Institute of Nanotechnology show that the NW arrays with wire widths down to 25 nm are FM at 300 K. These NW arrays display an easier approach towards magnetic saturation for a magnetic field applied parallel to the wire length than across the structure.
The in-plane uniaxial anisotropy is dominated by the shape of the wires and is preserved at low temperatures (10 K). The group also reports on the magnetization reversal properties of the Co NW arrays, which depends on the thickness of NWs. This process is governed by the curling mode reversal for thick wires, whereas thinner wires exhibit a more complex behaviour related to thermal effects and size distribution of the crystal grains that constitute the NWs.
More information can be found in the journal Nanotechnology.
About the author
The study was conducted by researchers from the Applied Physic group, CRANN & School of Physics, Trinity College Dublin, Ireland, in collaboration with the Catalan Institute of Nanotechnology (ICN), Barcelona, Spain. Dr S K Arora is a Senior Research Fellow in the Applied Physics Group at Trinity College Dublin. He specializes in self-assembly-based methods for synthesizing magnetic nanostructures and techniques for characterizing the materials. The Applied Physics group is headed by Prof. Igor Shvets, and consists of about 20 researchers working on a wide variety of topics including surface science, energy materials and nanomagnetics. Prof. Gambardella is head of the Atomic Manipulation and Spectroscopy Group at ICN, and focuses on fundamental concepts in magnetism and molecular electronics.