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S6.20.1

SELF-ASSEMBLING MAGNETIC NANOSTRUCTURES: WIRES, HELICES, NANOTUBES OF Ni NANOPARTICLES V.V.Kislov1, Yu.V.Gulyaev1, I.V.Taranov1, V.V.Kashin1, V.M. Kozhevin2, D.A. Yavsin2, M.A. Zabelin2, P.A. Tret’yakov2 and S.A. Gurevich2 1

Institute of Radioengineering & Electronics, Russian Academy of Sciences, 11 Mokhovaya, bld. 7, Moscow, 125009, Russia, [email protected] 2 Ioffe Institute, Russian Academy of Sciences, 26, Politekhnicheskaya, St. Petersburg, 194021, Russia ABSTRACT The formation of organized structures of magnetic nanoparticles have been studied by scanning probe microscopy when depositing Ni nanoclusters on conducting (gold on HOPG) substrates. In this case magnetic Ni nanoparticles formed by laser electrodispersion technique based on laser ablation (size of particles ~ 2.5 nm) form highly ordered superstructures, including helical (double helix with outer diameter ~ 10 nm, distance between sequences ~ 5 nm, length of such helix is typically hundreds of nm), linear (chains of clusters), etc. The structures discovered were investigated also by STS methods, with clear demonstration of Coulomb blockade effect over single nanoclusters. The results of calculations for dipole-dipole and exchange interaction of magnetic nanoparticles support such formation of helix-like structures. 1. INTRODUCTION Molecular nanoclusters (MNC) are playing increasingly important role as building blocks for electronic, catalytic, medical applications [1-3]. Within last 10 years considerable efforts were devoted to manufacturing of MNC with complex structure [1, 2] or nanoparticles (NP) [3], including magnetic NP. Metal NP are of considerable interest for their potential role for the design of novel electronic and magnetic devices, including data storage [4]. Typically metal NP should be less than 10 nm in size, forming organized structures in a highly controllable manner. Unfortunately, modern nanolithography facilities are very complicated and so very expensive. Self-assembling of metal NP and, in particular, magnetic NP provides an alternative and relatively inexpensive method of creating organized nanostructures. The discovery of helical nanostructures and linear chains of magnetic Ni NP, described in this work, requests some better understanding of individual and collective properties of NP and open the way for some interesting applications. 2. FABRICATION OF MAGNETIC NP Magnetic Ni NP were fabricated by laser electrodispersion technique [3] and deposited on specially prepared substrates (gold on HOPG) for further investigation by STM/STS methods of

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individual properties and structure formation for such metal NP. In this technique metal NP are generated in laser torch plasma and they are negatively charged when arriving to the substrate, and have very well defined size of ~ 2.5 nm. The size dispersion is less than 5%. Since Ni NP are amorphous, they do not coagulated even when the neighboring particles touch each other. Thin films of such NP are highly stable against oxidation. The presence of magnetic moments of