Processing of anisotropic MnBi nanoparticles by surfactant assisted ball milling K. Kanari 1 , C. Sarafidis 1 , M. Gjoka 2 , D. Niarchos 2 and O. Kalogirou 1 1 Dept. of Physics, Aristotle University of Thessaloniki, 54006 Thessaloniki, Greece 2 INN, NCSR Demokritos, Athens 15310, Greece E-mail: hsara@physics.auth.gr Nowadays, the field of magnetic applications is dominated by high performance permanent magnets based on rare-earth metals, due to their high values in maximum energy product, as high as 56 MGOe [1]. However, the high cost along with the limited supplies of rare-earth elements resulted in research trying to find potential substitutions, free of any rare-earth magnets. Unfortunately, the rare-earth-free permanent magnets have exhibit low energy products, a key characteristic for advanced applications, that is necessary to improve [2]. The intermetallic compound MnBi is a rare-earth-free, promising permanent magnetic material, with unique structure and temperature-dependent magnetic properties that recently has attracted a lot of interest. The low temperature phase (LTP) has a large magnetocrystalline anisotropy (K ≈10 7 erg cm -3 ) [2] due to its hexagonal NiAs crystal structure and a positive temperature coefficient of coercivity HC [3], which makes it an excellent candidate for high temperature applications. The unique temperature dependent behavior of MnBi is a result of the variation of the crystal lattice ratio of c/a with temperature [1]. Due to the peritectic reaction of Mn with Bi, which leads Bi to segregate from MnBi below the temperature of 446 o C [3], it is a rather challenging task to prepare single- phase particles of MnBi. A lot of conventional methods have been used, such as arc- melting, rapid solidification and sintering, with the best results, more than 90% of the LTP MnBi coming from melt-spinnin.[4] In our research we are following a mechanochemical approach, with surfactant assisted ball milling using Fritsch Pulverisette mill. First, MnBi ingots were arc-melted under Ar atmosphere and they were subsequently annealed, to optimize the dispersion of Mn and Bi inside the ingots. Then, they were grinned, until the particles were smaller than 50 μm. The MnBi powder was mechanically milled along with oleic acid, as the surfactant and hexane as the dispersant. The BPR was 10:1 and the time of milling varied, from 30 to 170 minutes. The particles of each sample were left to dry in air and then were characterized. The crystal structure of the as-milled samples as well as the initial MnBi, were examined by X-ray powder diffraction (XRD) and the total chemical composition was measured with EDS. Microstructural characterization was carried out using scanning electron microscopy (SEM) and magnetic hysteresis loops were measured using a vibrating sample magnetometer (VSM).