Delivered by Ingenta to: Guest User IP : 117.195.195.181 Wed, 10 Feb 2010 00:33:11 Copyright © 2010 American Scientific Publishers All rights reserved Printed in the United States of America RESEARCH ARTICLE Advanced Science Letters Vol. 3, 87–92, 2010 Multiwalled Carbon Nanotube-Coated SmCo 5 /Fe Magnetic Nanocomposites Processed by Magnetic Field-Assisted Ball Milling Padmanapan Saravanan ∗ , Partha Ghosal, and Venkatasubramanian Chandrasekaran Defence Metallurgical Research Laboratory, Hyderabad 500058, India Nanostructured anisotropic hard magnetic particles of SmCo 5 /Fe coated with multiwalled carbon nanotubes (MWNTs) were prepared by magnetic field-assisted ball milling technique. The MWNT-coated SmCo 5 /Fe pow- ders so obtained by this method exhibit interesting features such as flake-like morphology, reduction in particle size, anisotropy and high coercivity. The MWNT-coated SmCo 5 /Fe powders were further processed in the form of polymer nanocomposites under aligning magnetic field and were characterized for their structural and mag- netic properties. TEM analysis reveals the uniform coating of MWNTs in the form of disordered/amorphous carbon on the milled SmCo 5 /Fe powder particles. Magnetic measurements suggest that the addition of MWNTs with SmCo 5 /Fe brings new capabilities for the nanocomposite magnets in terms of higher coercivity (H c = 126 kOe), strong magnetic texture (M r /M max = 082) and percolation of SmCo 5 /Fe particles within the epoxy matrix. 1. INTRODUCTION The novel properties of carbon nanotubes (CNTs) 1–3 have gen- erated scientific and technical interest in the development of nanotubes-reinforced polymer composites. 4–6 The exceptionally high mechanical, electrical and thermal properties of CNTs make them ideal candidates as filler in light weight polymer composite. Besides their extraordinary mechanical properties (exceptionally high tensile strength and stiffness), the presence of large mag- netic susceptibility with strong anisotropy 7–9 —has further pro- moted research on the fabrication of nanotubes based magnetic composite materials. Many researchers have demonstrated the existence of anisotropic magnetic susceptibility of multiwalled carbon nanotubes (MWNTs), experimentally. 10 11 The magnetic susceptibility of partially aligned MWNT/polymer composites as function of temperature and magnetic field has been investigated by Tsui et al. 10 Similarly, the anisotropy of the MWNT polymer composites was studied by Kimura et al. through transmission electron microscopy (TEM), electrical, magnetic and mechani- cal property measurements. 11 The above remarkable properties of CNTs, i.e., the magnetic susceptibility associated with the strong anisotropy distinguishes this material from the other car- bon materials such as, fullerene, carbon black and graphite and represents CNTs as excellent candidates for the processing of polymer nanocomposites. It is for the above reasons, the MWNTs ∗ Author to whom correspondence should be addressed. have been chosen as a filler material for improving the perfor- mance of SmCo 5 /Fe magnetic nanocomposites. Recently, SmCo 5 /Fe-type nanocomposite exchange coupled magnets—which combine both the high anisotropy of hard magnetic phase (SmCo 5  with the large magnetization of the soft magnetic phase (Fe), have attracted greater attention for their potential to offer very high energy products. 12–14 Most of the preparation techniques reported for the SmCo 5 /Fe powders mainly uses high energy ball milling; nevertheless, the powder particles produced with this technique possess wide size distri- bution and, generally, they are magnetically isotropic and hence, not suitable for making anisotropic hard magnets. Consequently, many efforts have been made to transfigure the milling pro- cess through introducing either surfactant 15 or magnetic field 16 during conventional ball milling (referred as surfactant- or mag- netic field-assisted ball milling) to achieve anisotropic hard mag- netic particles with nanosized grains. Wang et al. 17 employed a surfactant-assisted milling technique to synthesize nanoparticles of Sm 2 Co 17 and SmCo 5 systems with sizes of about 50 nm, using oleic acid and oleyl amine as surfactants. Similarly, the mecha- nism of field-induced anisotropy has also been demonstrated in submicrometere size particles of Nd 2 Fe 14 B and Sm 2 Co 17 , pre- pared by a magnetic field-assisted ball milling. 16 Besides, we have recently reported the processing SmCo 5 /Fe nanocomposite powders by introducing both surfactant and magnetic field simul- taneously during the milling process, so as to impart size reduc- tion as well as orientation of the nanocrystallites. 18 However, Adv. Sci. Lett. Vol. 3, No. 1, 2010 1936-6612/2010/3/087/006 doi:10.1166/asl.2010.1093 87