Li Heyun, Liang Yang, Tan Xiaohua, Xu Hui, Hu Pengfei, Ren Kezhi
Institute of Materials, School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China.
Materials (Basel). 2017 Sep 11;10(9):1062. doi: 10.3390/ma10091062.
Understanding the coercivity mechanism has had a substantial impact on developing economically more attractive RE-based (RE = rare earth) permanent materials because of price volatility of key RE metals (i.e., Nd and Dy) in recent years. In this work, we investigated the microstructure and magnetic properties of melt-spun (NdCe)FeCo₂B ribbons and annealed samples at 773 K for 15 min with 1 Tesla (T) magnetic field to better understand the coercivity mechanism. We found hard magnetic grains were surrounded by thin and continuous layers along the grain boundaries (GBs) with a high concentration of ferromagnetic elements (Fe + Co >74 at%). The obvious positive peak in the plot and the interaction domain structure observed by Lorentz magnetic microscopy indicate that there is strong exchange coupling interaction through the ferromagnetic GB phase between hard magnetic grains. The annealing in an applied magnetic field of 1 T increases the remanence by enhancing the exchange coupling interaction, leading to a maximum product energy (()) which is 16% higher than that of melt-spun ribbons. We also studied the temperature dependence of the coercivity in a temperature range of 300-500 K, and proposed that the coercivity of melt-spun (NdCe)FeCo₂B ribbons with ferromagnetic GB phase at room temperature was from the combination of strong domain-wall pinning and nucleation. The same mechanism works in the annealed ribbons.
由于近年来关键稀土金属（即钕和镝）价格波动，了解矫顽力机制对开发经济上更具吸引力的稀土基（RE = 稀土）永磁材料产生了重大影响。在这项工作中，我们研究了熔体纺丝（NdCe）FeCo₂B薄带以及在773 K下于1特斯拉（T）磁场中退火15分钟的样品的微观结构和磁性，以更好地理解矫顽力机制。我们发现硬磁晶粒被沿晶界（GBs）的薄而连续的层所包围，这些层中含有高浓度的铁磁元素（Fe + Co >74 at%）。 曲线中明显的正峰以及洛伦兹磁显微镜观察到的相互作用畴结构表明，硬磁晶粒之间通过铁磁晶界相存在强交换耦合相互作用。在1 T外加磁场中退火通过增强交换耦合相互作用提高了剩磁，导致最大磁能积（(BH)max）比熔体纺丝带高16%。我们还研究了300 - 500 K温度范围内矫顽力的温度依赖性，并提出室温下具有铁磁晶界相的熔体纺丝（NdCe）FeCo₂B薄带的矫顽力源于强畴壁钉扎和成核的组合。相同的机制在退火薄带中也起作用。
