Contents lists available at ScienceDirect Materials Characterization journal homepage: www.elsevier.com/locate/matchar Novel Ho(Ni 0.8 Co 0.2 ) 3 nanoflakes produced by high energy ball – milling Anna Bajorek a,b,⁎ , Clément Berger a,b,c , Krystian Prusik b,d , Marcin Wojtyniak a,b , Grażyna Chełkowska a,b a A. Chelkowski Institute of Physics, University of Silesia in Katowice, Uniwersytecka 4, 40 – 007 Katowice, Poland b Silesian Center for Education and Interdisciplinary Research, University of Silesia in Katowice, 75 Pulku Piechoty 1A, 41-500 Chorzów, Poland c L'Institut des Molécules et Matériaux du Mans, Université du Maine, Avenue Olivier Messiaen, 72085 Le Mans, France d Institute of Materials Science, University of Silesia in Katowice, 75 Pulku Piechoty 1A, 41-500 Chorzów, Poland ARTICLE INFO Keywords: Intermetallics Mechanical milling Nanostructured materials Magnetic properties X-ray photoelectron spectroscopy (XPS) ABSTRACT The morphology and magnetic properties of bulk crystalline and ball – milled Ho(Ni 0.8 Co 0.2 ) 3 intermetallic compounds were studied. The influence of the duration of the high energy ball - milling (HEBM) for the final size of particles and crystallites was confirmed by a variety of complementary measurement methods. The crystal- lization of all studied specimens in the PuNi 3 type of crystal structure was confirmed. The presence of an amorphous phase was evidenced at the final stage of pulverization. The influence of different grinding times is reflected in the variation of morphology and magnetism of as-milled powders. An emergence of nanoflakes having nanoflower-like morphology was found at the end of HEBM process. Furthermore, a slight variation of magnetic parameter was observed. Potential coating of the nanoflakes by Ni/Co oxides was demonstrated by XPS investigations. 1. Introduction The high energy ball-milling (HEBM) has attracted a lot of attention as a method used for production rare - earth based intermetallic nanopowders with a controllable sizes, shapes and magnetic properties [1–6]. The nanomaterials obtained in such a way are highly promising for the development of nanocomposite magnets with enhanced mag- netic properties [1–6]. The control of various HEBM parameters e.g. the grinding time, atmosphere, ball to powder ratio or type of milling media helps to manufacture and design nanostructured materials with appropriate crystal structure, morphology and enhanced coercivity [1,2,6–32,34–40,41–53]. Recently, a substantial progress has been achieved in preparation of surfactant assisted HEBM samarium – cobalt compounds having 1:5 [7–18,22–24,31], 1:3 [25], or 2:17 [19,20] ratios. Nonetheless, various other nanosized intermetallics are also proposed for advanced perma- nent magnets applications [26–42]. Furthermore, in a past few years, intermetallics with 1:2 [43–45] or 1:3 structure obtained via HEBM have been studied [46–49,51–53]. Usually, for all rare-earth based powders the presence of irregular flakes was found. The variation of morphology across milling involves the change of anisotropy and causes the subsequent modification within magnetic parameters. Ob- viously, in the case of R-T materials such modification is also based on the mixture of localized 4f (R) and itinerant 3d (T) magnetism, which plays an important role not only in bulk compounds [54–76], but also in their nanostructured analogues. Therefore, the application of HEBM into bulk R-T intermetallics causes not only a change of remanence or coercivity, but also in many cases results in a deformation of the hysteresis loop [1,2,49–53,77–81]. The first aim of our study was to improve magnetic parameters of the bulk crystalline Ho(Ni 0.8 Co 0.2 ) 3 compound by its synthesis via HEBM. The second aim was focused on the influence of ball - milling parameters on the morphology and magnetism in as – milled nano- powders in a function of applied pulverization time. It is worth mentioning, that there is no published data about the bulk and nanostructured Ho(Ni 0.8 Co 0.2 ) 3 specimens. 2. Experimental The Ho(Ni 0.8 Co 0.2 ) 3 compound was prepared by arc melting from high purity elements (Ho - Rare Earth Product Limited – 99.99 wt%, Ni and Co Johnson Matthey Chemicals – spectrographically standardized) under argon atmosphere. The ingot was melted several times in order to obtain homogeneity. Afterwards, the as-cast sample was wrapped in http://dx.doi.org/10.1016/j.matchar.2017.03.035 Received 16 January 2017; Received in revised form 22 March 2017; Accepted 22 March 2017 ⁎ Corresponding author at: A. Chełkowski Institute of Physics, University of Silesia in Katowice, Silesian Center for Education and Interdisciplinary Research, 75 Pułku Piechoty 1A, 41- 500 Chorzów, Poland. E-mail addresses: anna.bajorek@us.edu.pl (A. Bajorek), clement-berger@neuf.fr (C. Berger), krystian.prusik@us.edu.pl (K. Prusik), marcin.wojtyniak@us.edu.pl (M. Wojtyniak), grazyna.chelkowska@us.edu.pl (G. Chełkowska). Materials Characterization 128 (2017) 43–53 Available online 23 March 2017 1044-5803/ © 2017 Elsevier Inc. All rights reserved. MARK