Structure and Magnetic Properties of MnBi Nanoparticles Prepared by Laser Ablation and Arc-Discharge Method

The Mn-Bi nanoparticles were prepared by using laser ablation and arc-discharge method, respectively. The arc-evaporated Mn-Bi nanoparticles exhibit ideal spherical shape with size in the range of several tens of nanometers to several hundreds of nanometers, whereas the laser-ablated Mn-Bi nanoparticles exhibit an irregular shape with smaller particle size. The Bi content in the arc-evaporated Mn-Bi nanoparticles was significantly enhanced compared to that of the Mn-Bi master alloys because of the higher vapor pressure of Bi than that of Mn in the melt. The Mn content in the arc-evaporated Mn-Bi nanoparticles increases with increasing Mn content in the master alloys. However, the Bi and Mn contents in the laser-ablated nanoparticles deviate little from that of the master alloys because of the highly localized molten pool of MnBi over the surface of the master alloys and the higher temperature reached using laser beams. The fraction of the low-temperature phase MnBi in the nanoparticles prepared by both methods increases with increasing annealing temperature and time. The laser ablation method is more effective in controlling the composition of the products. The coercivities of the arc-evaporated and laser-ablated Mn-Bi nanoparticles after annealing reached up to 0.65 and 0.8 T, respectively. The saturation magnetization of the annealed laser-ablated Mn-Bi nanoparticles reaches up to 51.6 Am-2/kg.