Magnetic, structural and thermal properties of the Finemet-type powders prepared by mechanical alloying S. Alleg a,n , S. Kartout b , M. Ibrir a , S. Azzaza a , N.E. Fenineche c , J.J. Sun ˜ol d a Laboratoire de Magne ´tisme et Spectroscopie des Solides, De´partement de Physique, Universite´ Badji Mokhtar, Annaba, B.P. 12, 23000 Annaba, Alge´rie b De´partement des Sciences Fondamentales, Universite´ du 20 Aou ˆt 1955 Skikda, Alge´rie c LERMPS, Universite´ de Technologie de Belfort Montbelliard, 90010 Belfort Cedex, France d Department de Fisica, Universitat de Girona, Campus Montilivi, Girona 17071, Spain article info Article history: Received 1 September 2012 Received in revised form 24 November 2012 Accepted 3 December 2012 Available online 22 December 2012 Keywords: A. Nanostructures C. X-ray diffraction D. Microstructure D. Magnetic properties abstract The mechanical alloying process has been used to prepare nanocrystalline Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 powders in a high energy planetary ball-mill Retsch PM400/2. Morphological, microstructural, structural, thermal and magnetic characterizations of the powders milled several times were investigated by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and hysteresis meter. A mixture of Fe(Si)-type nanograins (14 nm), Fe 2 B boride phase ( 12 nm), and bcc substitutional Fe(B)-type solid solution is obtained after 150 h of milling. The coercivity and saturation magnetization values are about 62 Oe and 14 emu/g, respectively. Several magnetic transition temperatures are revealed in the DSC scans of the ball-milled powders in the temperature ranges 500–560 1C and 599–606 1C, related to the Fe(B) and Fe(Si)-type phases, respectively. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Mechanical alloying (MA) has received special attention as a powerful non-equilibrium process which allows the preparation of amorphous, nanocrystalline (NC), intermetallic, supersaturated solid solutions, nanocomposites, etc. [1–5]. Because of the impor- tant fraction of atoms residing in grain boundaries, NC materials exhibit different physical, mechanical and magnetic properties from those of conventional coarse grains materials [6,7]. Fe–Si–B alloys with addition of Cu and Nb have been studied and used for many years since they exhibit good soft magnetic properties and are promising candidates for wide applications in technology such as power transformers, inductors, components for data communication interface, etc. [8–10]. The most fre- quently studied composition of Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 (known as Finemet) is of both physical and technical interest due to its high saturation magnetization, M s , low coercivity, H c , and high Curie temperature, T C , that are coupled with extreme brittleness when the optimum magnetic properties are reached [11,12]. The mag- netic softness of NC Finemet mainly arises from the dispersion of ultrafine a-Fe(Si) grains in an amorphous matrix which reduces the effective magnetic anisotropy and magnetostriction. The average anisotropy for randomly oriented a-Fe(Si) grains is negligibly small when the grain diameter does not exceed  15 nm [13]. The formation of NC bcc-Fe(Si) grains can be related to the small amount of alloying elements such as Cu and Nb which are grain boundary segregants. Indeed, Cu acts as nucleat- ing element for the bcc-Fe(Si) formation while the Nb hinders their growth [14,15]. The mechanical alloying process has been used to prepare NC Finemet powders starting from (i) rapidly quenched amorphous ribbons [16], (ii) NC ribbons obtained by thermal annealing at high temperature [17], (iii) Finemet powder prepared by high- speed water spray method [18], and (iv) pure elemental powders [19–21]. Mechanical grinding of amorphous ribbons for 140 h led to a very fine NC phase (10 nm) with a large fraction of grain boundaries [16], whereas nanostructured ribbons obtained from the crystallization of amorphous state by a proper annealing treatment could be changed into amorphous powder via short milling time, and return to crystallization on further milling [17]. The coercivity of the mechanically alloyed Finemet powders is much larger than that of the melt-spun ribbons, though the saturation magnetization is the same. This was attributed to the weakening of ferromagnetic coupling between the a-Fe(Si) nano- grains due to the absence of a grain boundary amorphous ferromagnetic phase [19]. The Finemet alloys show superpara- magnetic behavior for very small grain sizes [20,21]. The aim of the present study is to produce nanostructured Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 powders by MA in a high energy ball-mill Retsch PM400/2. X-ray diffraction (XRD), scanning electron Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jpcs Journal of Physics and Chemistry of Solids 0022-3697/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jpcs.2012.12.002 n Corresponding author. Tel./fax: þ213 38 87 53 99. E-mail addresses: safia_alleg@yahoo.fr, alleg.safia@univ-annaba.org (S. Alleg). Journal of Physics and Chemistry of Solids 74 (2013) 550–557