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Description
This work presents an alternative method to reduce the Mn particle size by adding glycerine during the ball-milling process. This glycerin addition is expected to prevent particle agglomeration to achieve the small and non-gathered Mn particles. The Mn and Bi precursors were fixed at an atomic ratio of 1:1 using Mn particles which were ball-milled in glycerin between 1 and 6 hr. It is seen that the average particle size decreases from 35-40 µm to 15-20 µm after 1 and 6 hr grinding time, respectively. The low-temperature phase MnBi (LTP-MnBi) was prepared by vacuum sintering technique using a sintering temperature of 275 ^oC for 12 hours under an ultra-high vacuum (≈10^-8 mbar). The sintered LTP-MnBi samples prepared from 1 (MnG_1Bi), 3 (MnG_3Bi), and 6 hr (MnG_6Bi) glycerine-added Mn grinding time were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS) and vibrating sample magnetometry. The coercivity values (H_c) are 3.95, 2.35, and 0.95 kOe for MnG_1Bi, MnG_3Bi, and MnG_6Bi samples, respectively. The saturation magnetization (M_s) of MnG_1Bi and MnG_3Bi are relatively similar (~0.18 emu/g), while the M_s of MnG_6Bi is much higher than those. The XRD result shows that there are a few percentages of MnBi concentration in all samples, implying that glycerin addition could hinder the MnBi formation. This could be explained by the interruption of the diffusion mechanism during liquid-phase sintering due to the coverage of hydrocarbon (i.e., NH_2-CH_2-COOH) groups on Mn particles. Moreover, from elemental composition analysis, it was found that the MnO content tends to increase on the Mn surfaces as the grinding time increases.
