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Soderberg O.,Aalto University | Brown D.,Magnequench Technology Center | Aaltio I.,Aalto University | Oksanen J.,Aalto University | And 3 more authors.
Journal of Alloys and Compounds | Year: 2011

Ni-Mn-Ga alloys were compacted using pulsed electric current sintering (PECS) at 850-875 °C (50 MPa, 8 min) of flake-like powders made from the rapidly quenched melt-spun ribbons. Two kinds of ribbons were used: one made with a relatively slow wheel speed (6 m/s; average grain size ∼14 μm), and another with a faster wheel speed (23 m/s; average grain size ∼5 μm). Both sets of flake-like powders consisted of a mixture of non-modulated martensite (NM) and seven-layered modulated martensite (7M) structure. The amount of NM was greater in the slower speed material, while the other one exhibited mostly the 7M structure. These crystal structures were inherited by the sintered samples. In the compacts having the NM structure the multi-step martensitic reaction overlapped with the magnetic transition, and the Curie temperatures during heating and cooling differed from each other. In the compacts having mainly 7M structure the Curie point was about 100 °C and the martensitic transition took place in the paramagnetic state, while the intermartensitic one occurred in the region of 60-85 °C. This material demonstrated good magnetic properties and saturation magnetization, at best ∼50 emu/g. Mechanical properties of the compacts were good, and comparable to those of the polycrystalline Ni-Mn-Ga samples in compression. © 2011 Elsevier B.V. All rights reserved.

Khosla A.,Simon Fraser University | Korcok J.L.,Simon Fraser University | Gray B.L.,Simon Fraser University | Leznoff D.B.,Simon Fraser University | And 3 more authors.
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2010

We present fabrication of a novel (Nd0.7Ce0.3) 10.5Fe83.9B5.6 magnetic powder and polydimethysiloxane bonded material that can be micropatterned into micromagnets. The magnetic powder, with an average particle size of 5μm-6μm, has been prepared from an alloy ingot of raw materials which are put in a vacuum induction furnace and melt spun to obtain ribbons with nanocrystalline microstructure. The ribbons are crushed using vibrating ball milling under inert atmosphere to obtain coarse powder (average particle size of 200μm). In order to obtain 5μm fine powder the course powder is jet milled at 6000rpm under inert atmosphere. The fine magnetic powder (referred to as MQFP-15) is ultrasonically uniformly dispersed in a polydimethylsiloxane matrix (PDMS) using a horn tip probe operating at a frequency of 42 kHz. Micromagnets (diameter of 50μm, height 30μm) are fabricated from the prepared composite via soft lithography and are tested using a SQUID magnetometer, showing a remanent magnetization (Mr) of 60.10 emu/g and coercivity (Hc) of 5260 G at 75 weight percentage of magnetic powder in the PDMS matrix. © 2010 SPIE.

Brown D.N.,Magnequench Technology Center
IEEE Transactions on Magnetics | Year: 2016

Over the last 30 years, rare-earth permanent magnets have become an integral part of our lives, driving computers, home appliances, and automobiles. They are set to become an even more prominent component of our future with the growth in clean technologies, such as electric vehicles and wind power generation. This market growth was briefly challenged in 2011 by the threat of supply restrictions and inflated prices from the world's principle source of rare earths. However, a rational calm has now returned to the market and magnet users can continue to benefit from the high efficiency and miniaturization these phenomenal magnets provide to electromechanical devices. The rare-earth magnet industry and research community continues to innovate and push these magnetic materials toward their theoretical potential, specifically in the areas of higher magnetic performance, lower costs, and greater thermal stability. These development areas for the two principle types of rare-earth iron boride (RE-Fe-B) magnet, sintered and rapidly quenched, are subtly different. The coarser microstructure of sintered magnets has made them more reliant on the less abundant heavy rare-earth elements for magnetic performance at elevated temperatures, so development activity on sintered RE-Fe-B magnets has focused on minimizing this Dy and Tb dependence. Magnets from rapidly quenched RE-Fe-B materials have fine nanostructures, and developments have targeted higher remanence, lower material costs, and protection of the material from oxidizing environments. © 2016 IEEE.

Chen Z.,Magnequench Technology Center | Lim Y.,Magnequench Technology Center | Brown D.,Magnequench Technology Center
2015 IEEE International Magnetics Conference, INTERMAG 2015 | Year: 2015

Melt spun Nd-Fe-B based powders have been successfully applied in bonded magnets for a wide variety of modern applications from power tools to automotive devices and computer components [1]. Critical factors that drive the development of such bonded magnets include: higher magnetic performance, better thermal stability and lower cost of alloy components. The latter point has become particularly important in recent years with the instability in the rare earth price and its availability [2]. This study looks into the effects of substituting the neodymium/praseodymium rare-earth component in melt-spun (NdPr)-Fe-B powders with the relatively low cost and abundant cerium element. © 2015 IEEE.

Chen Z.,Magnequench Technology Center | Miller D.,Magnequench Technology Center | Herchenroeder J.,Magnequench Technology Center
Journal of Applied Physics | Year: 2010

Isotropic Nd-Fe-B nanocrystalline fine powders with particle size in the range of 1-10μm have been developed using melt spinning and jet milling. The processing steps primarily consist of melt spinning Nd-Fe-B alloy to obtain ribbons with 25-50μm thickness, crushing the ribbon to obtain coarse powder with average particle size of about 200μm, and jet milling the coarse powder to obtain fine powder with average particle size of about 5-6μm. The effects of jet milling conditions on powder particle size, microstructure, and magnetic properties were systematically studied. For a magnet alloy nominally composed of Nd11.9 (Fe0.93 Co0.07) 82.6 B5.5, a particulate yield of D10 =2μm, D50 =6μm, and D90 =11μm and magnetic properties of Br=8.82 kG, Hci =9.5 kOe, and (BH) max =15.3 MGOe have been achieved in melt-spun and jet milled fine powders. The combined advantage of small particle size and high magnetic performance will make the Nd-Fe-B fine powder an attractive candidate for applications such as magnetic fluids, inks, micromachines, and flexible sheets. © 2010 American Institute of Physics.

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