A simple vacuum sintering system was set up to prepare low-temperature phase manganese-bismuth compound (LTP-MnBi). A mixture of Mn and Bi powders with 1:1 atomic ratio was sintered at 275 °C for 3, 6, 9 and 12 hours. The morphology of the sintered materials was investigated by SEM. The sintered product was further identified by XRD and energy dispersive spectroscopy and found to be LTP-MnBi, Mn and Bi. Sintering in vacuum could prevent the formation of manganese oxides. The magnetic properties of the sintered materials were characterized by using a vibrating sample magnetometer. The coercivity and the saturated magnetization were found to be 2.5 kOe and 42.4 emu/g, respectively. The maximum energy product of this magnetic materials was about 1.7 MGOe.
This work reports the changes in structural, chemical, and magnetic properties of the low-temperature phase manganese bismuth (LTP-MnBi) sintered from mixtures of Bi and Mn ball-milled for different times. The milling time was varied from 1 to 15 hr to produce Mn powder with different particle sizes. The average particle size reduced from ~400 µm (original size) to 35 ± 5 µm and 6 ± 2 µm after 1 and 15 hr milling times, respectively. The LTP-MnBi powder was sintered at 275 °C at vacuum pressure below 5 × 10−7 mbar for 12 hours. By increasing the Mn grinding time, the maximum energy product ((BH)max) of LTP-MnBi decreased from 1.98 ± 0.05 to 1.59 ± 0.07 MGOe, and the saturation magnetization (M s) decreased from 53.42 ± 0.90 to 44.32 ± 0.72 emu/g. The x-ray diffraction patterns indicated the reduction of LTP-MnBi content as a function of the milling time, which is agreed with the decrease in the M s value. This is supported by the x-ray photoelectron results, which also showed the increment of Mn oxides on the surface as a function of Mn milling time. The unexpected decrease in M s, which results in a significant reduction of magnetic performance, might be due to the presence of the oxides preventing diffusion during sintering.
An alternative way to increase a low-temperature phase MnBi (LTP-MnBi) content synthesized by low-temperature vacuum sintering is by using Mn powder with small particle sizes. To reduce the particle size by ball milling, glycine was added to prevent particle agglomeration and possible oxide formation. The ball-milled Mn and Bi powders were fixed at an atomic ratio of 1:1. The ball-milling time in glycine was between 1 and 3 hrs. The average particle size reduces from 400 µm (original) to 35-40 µm and 15-20 µm after grinding for 1 and 3 hr, respectively. Sintering of the mixtures was carried out at 275 °C for 12 hours at a vacuum pressure of less than 5×10−8 mbar. The LTP-MnBi samples sintered from 1 hr (MnG1Bi) and 3 hr (MnG3Bi) glycine-added Mn grinding times were investigated by XRD, SEM, XPS, and VSM. The coercivity values (H c) are 3.95 ± 0.04 and 2.35 ± 0.03 kOe for MnG1Bi and MnG3Bi, respectively. The saturation magnetization (M s) of MnG1Bi and MnG3Bi is relatively low (~0.18 emu/g) compared to the samples prepared by conventional ball-milling, i.e., without adding glycine in grinding. The XRD results show a few percentages of MnBi content in all samples, suggesting that glycine addition could prevent MnBi formation. The coverage of hydrocarbon (i.e., NH2-CH2-COOH) groups on Mn particles could prevent the diffusion mechanism during liquid-phase sintering. Moreover, it was found that the oxygen and carbon content in the MnGxBi were much higher than the conventional ball-milled MnBi.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.