Previous studies have shown that nanoscale magnetic systems exhibit novel properties not observed in the bulk material, including ferro- and superparamagnetism [1], which depend on the dimensionality and morphology of the system [2]. While it is well known that bulk metal cobalt atoms exhibit ferromagnetism when ordered in the hcp crystal structure, a complete understanding of their magnetic behavior when arranged in different nanoscale geometries is required in order to assess their potential for applications in nanostructured technological devices and may offer some insights into the scale-sensitive magnetic behaviors of other transition metals. Cobalt nanowires can be made to self-assemble at the step edges of a clean Pt(997) crystal under ultra-high vacuum conditions, where an appropriate deposition rate has been calculated to sputter the amount of cobalt necessary for the desired nanowire atomic width. Previous studies have been on the uncapped system [1], but any technological applications will require nanowires be protected with a non-magnetic, noble metal capping layer to prevent oxidation. We have studied cobalt nanowire systems capped with varying numbers of gold monolayers to analyze the dependence of nanowire magnetic behaviors on the thickness of the capping layer. Samples were examined via x-ray absorption spectroscopy at beamline I1011 at the MAX-lab synchrotron radiation source at the University of Lund in Sweden, and a protocol was established to effectively fit scans with a quadratic background to facilitate X-ray magnetic circular dichroism calculations. Potentially useful further studies include X-ray photoemission spectroscopy and imaging via scanning tunneling microscopy. A vacuum suitcase and supportive frame system have been designed and are under construction at Trinity College in Dublin, Ireland, to allow for sample transport between and into and out of the XPS and STM systems in the Center for Research on Adaptive Nanostructures and Nanodevices under UHV conditions in further studies.
References [1] P. Gambardella, A. Dallmeyer, K. Maiti, M. C. Malagoli, W. Eberhardt, K. Kern, and C. Carbone, “Ferromagnetism in one-dimensional monatomic metal chains,” Nature, vol. 416, no. 6878, pp. 301–304, Mar. 2002. [2] J. P. Cunniffe, D. E. McNally, M. Liberati, E. Arenholz, C. McGuinness, and J. F. McGilp, “X-ray magnetic circular dichroism and reflection anisotropy spectroscopy Kerr effect studies of capped magnetic nanowires,” physica status solidi (b), vol. 247, no. 8, pp. 2108–2112, 2010.