Abstract
Low-temperature phase (LTP) MnBi is considered as a promising rare-earth-free permanent magnetic material with high coercivity and unique positive temperature coefficient of coercivity. Mn55Bi45 ribbons with high purity of LTP MnBi phase were prepared by melt spinning. Then, Mn55Bi45 powders with different particle size were obtained by low-energy ball milling (LEBM) with and without added surfactant. The coercivity is enhanced in both cases. Microstructure characterization reveals that Mn55Bi45 powders obtained by surfactant assisted low-energy ball milling (SALEBM) have better particle size uniformity and show higher decomposition of LTP MnBi. Coercivity can achieve a value of 17.2 kOe and the saturation magnetization (Ms) is 16 emu/g when Mn55Bi45 powders milled about 10 h by SALEBM. Coercivity has achieved a maximum value of 18.2 kOe at room temperature, and 23.5 kOe at 380 K after 14 h of LEBM. Furthermore, Mn55Bi45 powders obtained by LEBM have better magnetic properties.
Highlights
Permanent magnets are indispensable components used in many vital areas including electric vehicles, medical equipment, high-energy product motors and generators, etc. [1,2]
It is difficult to obtain a single phase of Low-temperature phase (LTP) MnBi alloy, as Mn tends to segregate from the liquid phase below the peritectic temperature of 719 K [11,12]
In order to obtain high purity of LTP MnBi, Mn55 Bi45 ribbons were prepared by melt spinning at a speed of 40 m/s and subsequently annealed in vacuum
Summary
Permanent magnets are indispensable components used in many vital areas including electric vehicles, medical equipment, high-energy product motors and generators, etc. [1,2]. Low-temperature phase (LTP) MnBi has been considered as a promising rare-earth-free magnet with unique magnetic properties [7,8,9,10]. It is difficult to obtain a single phase of LTP MnBi alloy, as Mn tends to segregate from the liquid phase below the peritectic temperature of 719 K [11,12]. Mn55 Bi45 can promote the formation of high purity LTP MnBi alloy. When MnBi powders mixed with other magnetic materials, the MnBi-based composites with high magnetic performance will be obtained [13,14]. It is critical to this method that the size of the MnBi powders is comparable to the size of their single magnetic domain (~500 nm) in order to maximize the loading of the soft magnetic phase [15,16]. Low-energy ball milling (LEBM) is the most successful method for fabricating
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