A Mössbauer investigation of the formation of the Ni 3 Fe phase by high energy ball milling and subsequent annealing J.M. Le Breton a, * , O. Isnard b , J. Juraszek a , V. Pop c , I. Chicinas ¸ d a Groupe de Physique des Matériaux, UMR CNRS 6634, Université de Rouen, 76801 Saint Etienne du Rouvray, France b Institut Néel, CNRS, Université Joseph Fourier, 25 rue des martyrs, 38042 Grenoble, France c Faculty of Physics, Babes-Bolyai University, 400084 Cluj-Napoca, Romania d Department of Materials Science and Technology, Technical University of Cluj-Napoca, 400641 Cluj-Napoca, Romania article info Article history: Received 5 March 2012 Received in revised form 23 September 2012 Accepted 1 October 2012 Available online 16 January 2013 Keywords: A. Nanostructured intermetallics B. Microalloying C. Mechanical alloying and milling F. Spectroscopic methods, various abstract NieFe alloys obtained by high energy ball milling of pure Ni and Fe powders were investigated by 57 Fe Mössbauer spectrometry. The Mössbauer spectra of the as-milled powders were fitted with two magnetic contributions, corresponding to the a-Fe and NieFe phases. As the milling time increases, the relative intensity of the a-Fe contribution decreases while that of the NieFe phase increases. After about 10 h of milling, a NieFe phase with a composition close to Ni 3 Fe is obtained and no more a-Fe phase is present in the powder. The contribution of the NieFe phase is carefully investigated, and the value of the hyperfine field shows that Ni 3 Fe is formed in a disordered state. The influence of an annealing treatment at 330  C is discussed and compared to the results of both X-ray diffraction analysis and magnetic measurements previously obtained. Ó 2012 Published by Elsevier Ltd. 1. Introduction Ferromagnetic materials with excellent soft magnetic properties (high saturation magnetisation, high permeability, high Curie temperature and very low energy losses) are required for miniatur- isation and high frequency applications [1,2]. The NieFe and NieFee XeY polycrystalline alloys are well known for about a century and are widely studied for both fundamental properties and applications. The Ni 3 Fe intermetallic compound is situated around the Permalloy composition, and is considered as an excellent soft magnetic mate- rial due to the combination of low magnetocrystalline anisotropy and a nearly zero magnetostriction. The Ni 3 Fe compound crystallises in a face centred cubic structure (fcc) of AuCu 3 type Pm-3m space group, with lattice parameter a ¼ 0.35525 nm [3]. An orderedisorder structural transition is observed around 773 K [4], and Ni 3 Fe orders very slowly below this transition temperature [5,6]. On the other hand, the nanocrystalline state may exhibit superior properties compared with materials having polycrystalline structure, in nano- crystalline state magnetic materials having simultaneously low coercivity and high permeability [7]. Thus, soft magnetic materials based on nanocrystalline ferromagnetic powder present an improvement as compared with their microcrystalline counterparts, if their crystallite sizes are smaller than the characteristic length scales of the physical phenomena occurring in bulk materials. The exceptional properties of nanocrystalline materials are derived from their large number of atoms residing in defect environments (grain boundaries, interfaces, interphases, triple junctions) compared to coarse-grained polycrystalline counterparts [8e10]. For producing nanocrystalline/nanostructured materials, an alternative widely used technique to the incipient recrystallisation of the amorphous ribbons is mechanical alloying. This technique is used to produce non-equilibrium structures/microstructures including amorphous alloys, extended solid solutions, metastable crystalline phases, nanocrystalline materials and quasi crystals [11e 14]. Mechanical alloying is basically a dry high-energy milling process, in which elemental blends (or prealloyed powders, oxides, nitrides, etc.) are repeatedly welded, fractured and re-welded in order to achieve alloys or composite materials [13e16]. A brief presentation of all mechanical alloying/milling methods has been made in reference [13]. There is the possibility to combine the interesting properties of the nanocrystalline materials with the high soft magnetic proper- ties of the NieFe alloys. The research of NieFe powders produced by mechanical alloying has attracted much interest these last years leading to several studies [17e23], which covers the entire NieFe * Corresponding author. Tel.: þ33 2 32 95 50 39; fax: þ33 2 32 95 50 32. E-mail address: Jean-Marie.LeBreton@univ-rouen.fr (J.M. Le Breton). Contents lists available at SciVerse ScienceDirect Intermetallics journal homepage: www.elsevier.com/locate/intermet 0966-9795/$ e see front matter Ó 2012 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.intermet.2012.10.001 Intermetallics 35 (2013) 128e134