Bousnina Mohamed Ali, Dakhlaoui-Omrani Amel, Schoenstein Frédéric, Soumare Yaghoub, Barry Aliou Hamady, Piquemal Jean-Yves, Viau Guillaume, Mercone Silvana, Jouini Noureddine
Laboratoire des Sciences des Procédés et des Matériaux, CNRS, UPR 3407, Université Sorbonne Paris Nord, 99 Avenue J.B. Clément, F-93430 Villetaneuse, France.
Department of Chemistry, Faculty of Sciences and Arts-Khulais, University of Jeddah, Khulais P.O. Box 355, Jeddah 21921, Saudi Arabia.
Nanomaterials (Basel). 2020 Feb 15;10(2):334. doi: 10.3390/nano10020334.
Cobalt nano-rods with the hexagonal close-packed (hcp) structure were prepared by reduction of the long-chain carboxylate Co (II) precursor in polyol. The application of an external magnetic field ( = 1.25 T) during the nucleation and growth steps resulted in a noticeable modification of the mean aspect ratio (length/diameter) of the particles. The particle morphology was also modified as the nano-rods did not exhibit conical heads at their extremities anymore, which are observed for particles prepared without application of an external magnetic field. Besides, the stacking faults density along the axis of the hcp structure in the cobalt nano-rods has been found to decrease with the increase in the applied magnetic field. The coercive field of randomly oriented nano-rods increased with the aspect ratio, showing the highest value (i.e., 5.8 kOe at 300 K) for the cobalt nano-rods obtained under the highest applied magnetic field. For partially oriented Co nano-rods in toluene solution, the magnetic properties were significantly enhanced with a coercive field of 7.2 kOe at 140 K, while the magnetization saturation reached 92% of the bulk. The value was about 0.8, indicating a good orientation of the anisotropic particles relative to each other, making them suitable for the preparation of permanent magnets via a bottom-up approach.
通过在多元醇中还原长链羧酸盐钴（II）前驱体制备了具有六方密堆积（hcp）结构的钴纳米棒。在成核和生长步骤中施加外部磁场（ = 1.25 T）导致颗粒的平均长径比（长度/直径）发生明显变化。颗粒形态也发生了改变，因为纳米棒在其末端不再呈现锥形头部，而在未施加外部磁场制备的颗粒中会观察到这种锥形头部。此外，已发现钴纳米棒中沿hcp结构的 轴的堆垛层错密度随着施加磁场的增加而降低。随机取向的纳米棒的矫顽场随着长径比的增加而增加，对于在最高施加磁场下获得的钴纳米棒，显示出最高值（即在300 K时为5.8 kOe）。对于甲苯溶液中部分取向的钴纳米棒，磁性能显著增强，在140 K时矫顽场为7.2 kOe，而磁化饱和度达到块体的92%。 值约为0.8，表明各向异性颗粒彼此之间具有良好的取向，使其适合通过自下而上的方法制备永磁体。
