INSTITUTE OF PHYSICS PUBLISHING NANOTECHNOLOGY Nanotechnology 15 (2004) 520–524 PII: S0957-4484(04)67808-1 The effect of carbon encapsulation on the magnetic properties of Ni nanoparticles produced by arc discharge in de-ionized water K H Ang 1 , I Alexandrou 2 , N D Mathur 3 , G A J Amaratunga 1 and S Haq 4 1 Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK 2 Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, UK 3 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, UK 4 BAE Systems, Advanced Technology Centre, PO BOX 5, Filton, FPC 267, Bristol BS34 7QW, UK Received 13 August 2003 Published 13 February 2004 Online at stacks.iop.org/Nano/15/520 (DOI: 10.1088/0957-4484/15/5/020) Abstract Despite intensive research on optimizing the methods for depositing carbon encapsulated ferromagnetic nanoparticles, the effect of the carbon cages remains unclear. In the present work, the effect of the graphitic cages on the magnetization of the ferromagnetic core has been studied by comparing the magnetic properties of pure and carbon encapsulated Ni particles of the same size. The carbon encapsulated Ni particles were formed using an electric arc discharge in de-ionized water between a solid graphite cathode and an anode consisting of Ni and C in a mass ratio of Ni:C = 7:3. This method is shown to have potential for low cost production of carbon encapsulated Ni nanoparticle samples with narrow particle size distributions. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) analysis were used to study the crystallography, morphology, and size distribution of the encapsulated and pure Ni nanoparticle samples. The availability of encapsulated particles with various sizes allowed us to elucidate the role of carbon cages in size-dependent properties. Our data suggest that even though encapsulation is beneficial for protection against hostile chemical environments and for avoiding low proximity phenomena, it suppresses the saturation magnetization of the Ni cores. (Some figures in this article are in colour only in the electronic version) 1. Introduction Carbon encapsulated ferromagnetic nanoparticles have received considerable attention in recent years because of their potential as small magnetic clusters in high density magnetic data storage, in ferrofluid applications, and magnetic resonance imaging [1]. Enclosure of nanometre-sized magnetic particles in carbon capsules is of particular interest since it could prevent their degradation in reactive chemical environments and isolate the particles magnetically from each other to avoid low proximity interactions [2]. To date, most research work has been concentrated on the synthesis of encapsulated ferromagnetic nanoparticles [3–5]. Since the main technological interest in this type of material concerns magnetic applications, in this work a comparison of the magnetic properties of carbon encapsulated Ni particles (produced by arc discharge in de-ionized water) and pure Ni particles (produced commercially) of the same size is made. 0957-4484/04/050520+05$30.00 © 2004 IOP Publishing Ltd Printed in the UK 520