IOP PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS J. Phys. D: Appl. Phys. 40 (2007) 5021–5026 doi:10.1088/0022-3727/40/17/002 SmCo 5 /Fe nanocomposite magnetic powders processed by magnetic field-assisted ball milling with and without surfactant P Saravanan, R Gopalan 1 , N V Rama Rao, M Manivel Raja and V Chandrasekaran Defence Metallurgical Research Laboratory, Kanchanbagh PO, Hyderabad 500 058, India E-mail: rg gopy@yahoo.com and gopalan@dmrl.ernet.in Received 26 April 2007, in final form 16 July 2007 Published 16 August 2007 Online at stacks.iop.org/JPhysD/40/5021 Abstract A magnetic field-assisted ball milling has been employed for the preparation of SmCo 5 + 10 wt% Fe nanocomposite powders in the presence of oleic acid as surfactant. Milling experiments were also carried out without using surfactant and the nanocomposite powders so obtained, with and without surfactant, were investigated for their structural and magnetic properties using SEM, XRD, VSM and M ¨ ossbauer spectrometry. The field-milled SmCo 5 /Fe nanopowders in the presence of surfactant display a possible grain orientation and possess relatively high coercivity as compared with that of SmCo 5 /Fe powders obtained with field-milling or conventional milling. M¨ ossbauer studies revealed that the formation of α-Fe(Co) (soft magnetic phase) is more pronounced for the powders milled without surfactant. (Some figures in this article are in colour only in the electronic version) 1. Introduction Rare earth (RE)–transition metal (TM) based intermetallic compounds are technologically important materials for permanent magnet applications. Among all the RE–TM magnets, SmCo 5 is an attractive candidate for hard magnet applications due to their high Curie temperature (T c ), high magnetocrystalline anisotropy (H A ) and relatively high energy product [(BH) max . ][1–3]. A milestone in energy product (20 MGOe) has been realized via liquid phase sintering of field-oriented powder of SmCo 5 [4]. The SmCo 5 magnet technology has reached saturation in achieving the maximum energy product close to its theoretical limit. To enhance the practically achieved values close to the threshold value, innovative approaches are called for to go beyond conventional technologies. In this context, ‘nanotechnology’ comes in handy. It is well known that at the nanolevels (10 -9 m) the properties of the materials are entirely different from those at 1 Author to whom any correspondence should be addressed. the macro levels and nanotechnology is based on this fact so that the new set of properties can be exploited. In particular, nanotechnology is so relevant in magnetic materials—as atomic magnetism controls the bulk properties [5, 6]. Usually, magnetic materials exist with either high coercivity or high magnetization, but both the properties are required for high energy magnets. The basic principle in the nanocomposite permanent magnet is to exchange couple a hard magnetic phase having high coercivity with a soft phase of very large magnetization (both the phases must be in nanosize). In this context, hard magnet research is directed towards the development of nanocomposite magnets based on Nd–Fe–B (hard)/Fe (soft) and Sm–Co(hard)/Fe(Co) (soft) phases, wherein the hard phase provides coercivity and the soft phase offers magnetization. High energy ball milling [7], mechanical alloying [8], sputtering [9] and melt spinning [10] are usually adopted as the process methodologies to prepare nanocomposite magnets. For example, Zhang et al have demonstrated high energy product (∼32 MGOe) in Sm(Co,Cu) 5 /Fe nanocomposite thin films [11]. On the 0022-3727/07/175021+06$30.00 © 2007 IOP Publishing Ltd Printed in the UK 5021