Cobalt nanoparticles with preferential hcp structure: A confirmation by X-ray diffraction and NMR Vladimir V. Matveev a , Dmitry A. Baranov b , Gleb Yu. Yurkov b, * , Nikita G. Akatiev a , Ivan P. Dotsenko b , Sergey P. Gubin b a V.A. Fock Institute of Physics of Saint-Petersburg State University, 198504 Saint Petersburg, Russia b N.S. Kurnakov Institute of General and Inorganic Chemistry Russian Academy of Sciences, 119991 Moscow, Russia Received 26 December 2005; in final form 30 January 2006 Available online 6 March 2006 Abstract In this Letter, nanostructured materials consisting of cobalt nanoparticles and different matrixes and formed by universal thermal destruction method are presented. Ultradispersed polytetrafluoroethylene (UPTFE) and polyethylene were used as matrixes for surface or volume stabilization of nanoparticles. 59 Co NMR and X-ray diffraction methods were used to determine the structure of cobalt nano- particles. The NMR data confirmed mainly the presence of hcp-like crystalline structure. Ó 2006 Elsevier B.V. All rights reserved. 1. Introduction Nanometer-sized cobalt particles embedded in various matrixes or on the surface of different supports are prom- ising materials for high-density recording as well as for other technological applications [1–3]. The unique behavior of nanostructured systems is determined by both the prop- erties of nanoparticles and interaction with the matrix. In addition, magnetic nanoparticles placed on the surface of the nanogranules are very attractive as magnetic nanomar- kers and for the application in drug delivery [4]. Earlier our group reported about novel methods of sta- bilization of magnetic nanoparticles (iron and cobalt oxi- des, ferrites, and bimetallic nanoparticles) in the volume of polyethylene (PE) [5] and localization of the iron nano- particles on the surface of the polytetrafluoroethylene nanogranules [6]. Investigation of a structure of 4 nm sized cobalt nanoparticles immobilized in the PE by EXAFS method allowed us to suggest that the nanoparticles may have the hcp-like crystalline structure [7]. In this letter, we demonstrate the possibility of the immobilization of cobalt nanoparticles on the surface of UPTFE by the same method and confirm the preferential hcp-like structure of the particles both in PE and on UPTFE matrixes using XRD and NMR techniques. 2. Experimental section The materials containing magnetic nanoparticles (Fe, Fe x O y , Co, BaFe 2 O 4 , and Fe 1x Co x ) in the volume of PE matrix and iron-based particles on the surface of UPTFE may be prepared by the method of thermal decomposition as described earlier [5–9]. The main idea of the synthetic method is thermolysis of the metal-containing compound in the presence of the stabilizer (polymer). The one-pot sta- bilization of ‘hot’ nanoparticles by the matrix is one of the advantages of this approach. For the synthesis of nano- structured material consisting of Co nanoparticles stabi- lized on the surface of the UPTFE we used cobalt formate (Co(HCOO) 2 ) as a precursor. The average size of nanoparticles was determined by transmission electron microscopy (TEM) studies using JEOL JEM-100B microscope. Samples were dispersed in the solvent using an ultrasonic oscillator. A drop of the 0009-2614/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2006.02.099 * Corresponding author. Fax: +7 495 954 1279. E-mail addresses: vmatveev@esr.phys.spbu.ru (V.V. Matveev), gy- yurkov@yandex.ru (G.Yu. Yurkov), gubin@igic.ras.ru (S.P. Gubin). www.elsevier.com/locate/cplett Chemical Physics Letters 422 (2006) 402–405