Lee Chung-Hyo
Department of Advanced Materials Science and Engineering, Mokpo National University, Muan-gun, Chonnam, 58554, Korea.
J Nanosci Nanotechnol. 2018 Feb 1;18(2):1148-1151. doi: 10.1166/jnn.2018.14923.
We have applied mechanical alloying (MA) to produce nanocrystalline Co2MnAl Heusler alloys using a mixture of elemental Co50Mn25Al25 powders. An optimal milling and heat treatment conditions to obtain a Co2MnAl Heusler phase with fine microstructure were investigated by X-ray diffraction, differential scanning calorimeter and vibrating sample magnetometer measurements. α-(Co, Mn, Al) FCC phases coupled with amorphous phase are obtained after 3 hours of MA without any evidence for the formation of Co2MnAl alloys. On the other hand, a Co2MnAl Heusler alloys can be obtained by the heat treatment of all MA samples up to 650 °C. X-ray diffraction result shows that the average grain size of Co2MnAl Heusler alloys prepared by MA for 5 h and heat treatment is in the range of 95 nm. The saturation magnetization of MA powders decreases with MA time due to the magnetic dilution by alloying with nonmagnetic Mn and Al elements. The magnetic hardening due to the reduction of the grain size with ball milling is also observed. However, the saturation magnetization of MA powders after heat treatment increases with MA time and reaches to a maximum value of 105 emu/g after 5 h of MA. It can be also seen that the coercivity of 5 h MA sample annealed at 650 °C is fairly low value of 25 Oe.
我们采用机械合金化（MA）方法，使用元素Co50Mn25Al25粉末混合物来制备纳米晶Co2MnAl赫斯勒合金。通过X射线衍射、差示扫描量热仪和振动样品磁强计测量，研究了获得具有精细微观结构的Co2MnAl赫斯勒相的最佳球磨和热处理条件。在机械合金化3小时后，获得了与非晶相耦合的α-(Co, Mn, Al)面心立方相，没有任何形成Co2MnAl合金的迹象。另一方面，通过对所有机械合金化样品在高达650°C的温度下进行热处理，可以获得Co2MnAl赫斯勒合金。X射线衍射结果表明，通过机械合金化5小时并进行热处理制备的Co2MnAl赫斯勒合金的平均晶粒尺寸在95纳米范围内。由于与非磁性的Mn和Al元素合金化导致的磁稀释，机械合金化粉末的饱和磁化强度随机械合金化时间而降低。还观察到由于球磨导致晶粒尺寸减小而产生的磁硬化现象。然而，热处理后机械合金化粉末样品的饱和磁化强度随机械合金化时间增加，并在机械合金化5小时后达到最大值105 emu/g。还可以看出，在650°C退火的5小时机械合金化样品的矫顽力相当低，为25 Oe。
