Magnetic properties of carbon nano-particles produced by a pulsed arc submerged in ethanol N. Parkansky a, *, B. Alterkop a , R.L. Boxman a , G. Leitus b , O. Berkh c , Z. Barkay d , Yu. Rosenberg d , N. Eliaz e a Electrical Discharge and Plasma Laboratory, Tel Aviv University, P.O. Box 39040, Tel Aviv 69978, Israel b Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel c School of Electrical Engineering, Tel Aviv University, P.O. Box 39040, Tel Aviv 69978, Israel d Wolfson Applied Materials Research Center, Tel Aviv University, P.O. Box 39040, Tel Aviv 69978, Israel e School of Mechanical Engineering, Tel Aviv University, P.O. Box 39040, Tel Aviv 69978, Israel ARTICLE INFO Article history: Received 14 February 2007 Accepted 6 November 2007 Available online 21 November 2007 ABSTRACT Carbon powder was produced by a pulsed arc ignited between two carbon electrodes submerged in ethanol, and was comprised of both micro- and nano-particles. The mea- sured magnetic properties of the mixed ‘‘raw’’ powder at 20 and 300K were: saturation magnetization M s  0.90–0.93 emu/g, residual magnetization M r = 0.022 and 0.018 emu/g, and coercive force H c = 11 and 8 Oe, respectively. The data lead to conclusion that the pow- der consisted of ferromagnetic particles with a critical temperature much higher than 300 K. Magnetic particles in solution were separated by means of bio-ferrography. It was found that the magnetically separated particles included chains of 30–50 nm diameter spheres, and nanotubes and nanorods with lengths of 50–250 nm and diameters of 20– 30 nm. In contrast, the residual particles which passed through the bio-ferrograph con- sisted of 1 lm and larger micro-particles, and nano-particles without any definite shape. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction The possibility of macroscopic magnetic ordering in carbon particles is interesting because of their importance for phys- ics, chemistry and materials science. There may be applica- tions for them in engineering, and, because they are a unique biocompatible magnetic material, in medicine and biology as well [1,2]. Some experiments demonstrated the existence of weak ferromagnetic-like magnetization loops in highly-oriented pyrolytic graphite (HOPG) [3,4] and paramag- netism of a novel carbon nano-foam [5]. There have been theoretical and experimental demonstrations that ferromag- netism can existence in pure carbon [6–11], while other authors refute this possibility [12]. Possibly the coexistence of sp 3 and sp 2 bonds [1] and defects in graphite structures, such as pores, planar edges and topological defects, induce the observed magnetic properties. Thus, the magnetic proper- ties may depend on the particle production method, since it influences defect production. Recently, a novel method to produce carbon micro- and nano-particles using a pulsed arc submerged in liquid was developed [13,14]. A plasma bubble is formed, comprised of some combination of material evaporated and partially ion- ized from the electrodes and the liquid, and in some cases liquid droplets of the electrode material are also produced. Solid particles form when these liquid electrode droplets con- tact the surrounding liquid and when the materials in the bubble condense, either on contacting the surrounding liquid 0008-6223/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2007.11.008 * Corresponding author: Fax: +972 3 641 0189. E-mail address: naump@eng.tau.ac.il (N. Parkansky). CARBON 46 (2008) 215 – 219 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon