On the Structural and Magnetic Properties of Mn-Bi Alloy Jet Milled at Different Feed Rates
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ORIGINAL PAPER
On the Structural and Magnetic Properties of Mn-Bi Alloy Jet Milled at Different Feed Rates V. V. Ramakrishna 1,2 & S. Kavita 1 & T. Ramesh 2 & Ravi Gautam 1 & R. Gopalan 1 Received: 14 September 2020 / Accepted: 29 October 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Mn50Bi50 alloy was prepared using arc melting method with subsequent homogenization treatment. The homogenized alloy was crushed and subjected to jet mill at different feed rates. The weight fraction of the LTP MnBi phase determined by the Rietveld refinement of the XRD pattern was found to be 89% in the as-homogenized and crushed alloy. The crushed alloy was subjected to jet milling at different feed rates from 0.5 to 1.5 g/min. Structural studies show that increase in feed rate leads to phase decomposition. Magnetic studies show that as-homogenized crushed alloy exhibits a magnetization of 60 emu/g. Jet milling leads to increase in coercivity and a decrease in magnetization. However, it was found that increase in the feed rate during jet milling leads to decrease of both coercivity and magnetization. Microstructural studies show that jet milling leads to decrease in particle size. Jet milling done at a lower feed rate helps in yielding the lowest average particle size compared to remaining feed rates in the Mn-Bi alloy. The spin reorientation transition temperature of the Mn-Bi alloy decreases with jet milling and varies at different feed rates. The coercivity of the Mn-Bi powder jet milled with a lower feed rate increases from 14.7 kOe at room temperature to 19.4 kOe at 400 K. Keywords Rare-earth free permanent magnet . Mn-Bi . Jetmill . Magnetization . Coercivity
1 Introduction Owing to the scarcity and the high cost of rare earth elements, a significant number of studies concentrate on permanent magnets with alleviated rare earth elements or rare earth free permanent magnets [1–3]. Mn-based intermetallic ferromagnetic compounds have gained considerable interest due to their magnetic properties and anisotropy. Mn-Al, Mn-Bi, and Mn-Ga compounds have already been shown to be possible permanent magnets as an alternative to rare earth based permanent magnets [4]. Rare earth free MnBi in its low temperature phase (LTP) has received constant diligence due to its unusual magnetic properties like high uniaxial magneto crystalline anisotropy (the anisotropy constant K = 1.6 × 106 J/m3) at room temperature [2, 3] and positive temperature coefficient of coercivity. The formation of single-phase LTP
* S. Kavita [email protected] 1
International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Chennai, Tamil Nadu 600113, India
2
Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu 620015, India
MnBi is challenging [5]. There have been several attempts to obtain highly pure LTP MnBi by different processing routes such as arc melting [6], melt-spinning [7], induction melting [8], and spark erosion [9]. To prepare a bulk magn
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