MnBi has attracted much attention in recent years due to its potential as a rare-earth-free permanent magnet material. It is unique because its coercivity increases with increasing temperature, which makes it a good hard phase material for exchange coupling nanocomposite magnets. MnBi phase is difficult to obtain, partly because the reaction between Mn and Bi is peritectic, and partly because Mn reacts readily with oxygen. MnO formation is irreversible and harmful to magnet performance. In this paper, we report our efforts toward developing MnBi permanent magnets. To date, high purity MnBi (>90%) can be routinely produced in large quantities. The produced powder exhibits 74.6?emu?g?1 saturation magnetization at room temperature with 9?T applied field. After proper alignment, the maximum energy product (BH)max of the powder reached 11.9?MGOe, and that of the sintered bulk magnet reached 7.8?MGOe at room temperature. A comprehensive study of thermal stability shows that MnBi powder is stable up to 473?K in air. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. AbstractMnBi has attracted much attention in recent years due to its potential as a rare-earth-free permanent magnet material. It is unique because its coercivity increases with increasing temperature, which makes it a good hard phase material for exchange coupling nanocomposite magnets. MnBi phase is difficult to obtain, partly because the reaction between Mn and Bi is peritectic, and partly because Mn reacts readily with oxygen. MnO formation is irreversible and harmful to magnet performance. In this paper, we report our efforts toward developing MnBi permanent magnets. To date, high purity MnBi (>90%) can be routinely produced in large quantities. The produced powder exhibits 74.6 emu g −1 saturation magnetization at room temperature with 9 T applied field. After proper alignment, the maximum energy product (BH) max of the powder reached 11.9 MGOe, and that of the sintered bulk magnet reached 7.8 MGOe at room temperature. A comprehensive study of thermal stability shows that MnBi powder is stable up to 473 K in air.

Crystallographically anisotropic SmCo 5 nanoflakes were fabricated directly by one-step surfactant-assisted high energy ball milling ͑HEBM͒ of Sm 17 Co 83 ingot powders for 5 h in heptane and oleic acid ͑OA͒ without preprocessing or further annealing. The SmCo 5 nanoflakes have a strong ͓001͔ out-of-plane texture. The thickness of nanoflakes is in the range of 8-80 nm while their length is 0.5-8 m. The surfactant OA plays an important role in the formation of SmCo 5 nanoflakes. HEBM of SmCo 5 ingots in heptane without OA resulted in the formation of magnetically isotropic more or less equiaxed SmCo 5 particles with a size of 2 -30 m. Closely packed "kebablike" SmCo 5 nanoflakes were formed by HEBM in heptane with 15 wt % OA. HEBM in 150 wt % OA led to well-separated nanoflakes instead of the closely packed kebablike nanostructure. This resulted in the enhanced ͓001͔ out-of-plane texture. In-plane transmission electron microscope examination showed that the SmCo 5 nanoflakes were composed of grains with sizes in the range of 4-8 nm. Coercivities of about 18.0 kOe were obtained for the anisotropic SmCo 5 nanoflakes.Using surfactants during ball milling influences not only the size of the particles but also their shape. 1-3 For malleable metals and alloys, the shape of ball-milled particles can be controlled by varying the milling environment. Dry milling in gas yields more or less equiaxed particles, 2 whereas wet milling in the presence of a solvent and/or surfactants, particularly with a high energy mill and/or at a high ball-topowder ratio, results in high-aspect-ratio flakes, usually with a submicron thickness. 2,3 Flakes of Ni, Cu, Fe-Co, Fe-CoZr, Fe-Si-Al, Sn-Ag-Cu, etc., have been fabricated by wet ball milling. 2,3 However, the rare earth-transition metal ͑RE-TM͒ hard magnetic materials are inherently brittle and, therefore, usually are not susceptible for the "flaking" during ball milling. Until now, there are few reports on textured and magnetically anisotropic RE-TM nanoflakes. SmCo 5 based alloys have the highest room-temperature magnetocrystalline anisotropy among the RE-TM magnetic materials. 1 In this work, magnetically anisotropic SmCo 5 nanoflakes with the ͓001͔ out-of-plane texture were fabricated directly by onestep surfactant-assisted high energy ball milling ͑HEBM͒ of SmCo 5 ingot powders in heptane and oleic acid ͑OA͒ without prior processing or further annealing. The nanostructure and magnetic properties of the anisotropic SmCo 5 nanoflakes were studied in detail.Sm 17 Co 83 ͑at. %͒ alloy was prepared by arc melting with the appropriate excess of Sm ͑1.5-4 wt % depending on the ingot weights͒ to compensate for the evaporation losses. The ingots were manually crushed and grinded down to less than 300 m. HEBM of 5 g crushed powder was carried out for 5 h in hardened stainless steel vial using a SPEX-8000 ball mill. Heptane ͑99.8 %͒ was used as the ball-milling medium and OA ͑90 %͒ as the surfactant. The amounts of surfactant used were 0, 15, 40, and 150 wt % of the starting powders. The harden-...

High-energy ball milling has been shown to be a promising method for large-scale fabrication of rare earth-transition metal nanoparticles. In this work, we report crystallographically anisotropic SmCo(5), PrCo(5) and Sm(2)(Co, Fe)(17) nanoparticles (particle size smaller than 10 nm) obtained by surfactant-assisted ball milling and study their size and properties as a function of the milling conditions. By milling nanocrystalline precursor alloys, we obtained SmCo(5) platelets (flakes) approximately 100 nm thick with an aspect ratio as high as 10(2)-10(3). The unusual shape evolution of this brittle material is attributed to its increased plasticity in the nanocrystalline state. The nanoflakes are susceptible to re-crystallization annealing and exhibit a room-temperature coercivity of up to 19 kOe. The successful fabrication of rare earth-cobalt nanoparticles and ultra-thin flakes provides hope for the development of nanocomposite permanent magnets with an enhanced energy product.

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MnBi attracts great attention in recent years for its great potential as permanent magnetmaterials. MnBi phase is difficult to obtain because of the rather drastic peritectic reaction between Mn and Bi. In this paper, we report our effort on synthesizing high purity MnBi compound using conventional powder metallurgical approaches. Neutron diffraction was carried out to investigate the crystal and nuclear structure of the obtained powder. The result shows that the purity of the obtained powder is about 91 wt. % at 300 K, and the magnetic moment of the Mn atom in MnBi lattice is 4.424 and 4.013 μ B at 50 K and 300 K, respectively. MnBi attracts great attention in recent years for its great potential as permanent magnet materials. MnBi phase is difficult to obtain because of the rather drastic peritectic reaction between Mn and Bi. In this paper, we report our effort on synthesizing high purity MnBi compound using conventional powder metallurgical approaches. Neutron diffraction was carried out to investigate the crystal and nuclear structure of the obtained powder. The result shows that the purity of the obtained powder is about 91 wt. % at 300 K, and the magnetic moment of the Mn atom in MnBi lattice is 4.424 and 4.013 l B at 50 K and 300 K, respectively. V C 2014 AIP Publishing LLC.

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