Morphology control of magnetic properties in cobalt nanowires
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Cobalt nanowires with different shapes and sizes were synthesized by reduction of carboxylate salts of CoII in 1, 2-butanediol using a solvothermal chemical process. The well-crystallized Co nanowires with hexagonal close-packed (hcp) phase are observed and the (002) crystalline direction is along the long axis of nanowires. The morphology control is strongly dependent on the reaction parameters. By varying the amount of capping agent in proper ranges, the effect of reaction parameters on controlling the size and shape of Co nanowires is demonstrated. With the amount of capping agent increasing, the aspect ratio of Co nanowires increases remarkably. However, the magnetic measurement of cobalt nanowires shows that the coercivity of the Co nanocrystals does not increase with the increase in aspect ratio monotonously, which suggests that the tip shape and microstructure also play an important role in the magnetization reversal process of the Co nanocrystals, and the aspect ratio plays a much less role as the ratio value exceeds 11. To further understand the effect of size on the magnetic properties in the Co nanowires, micromagnetic simulations were performed, which confirms that the magnetic properties are barely affected by the aspect ratio larger than 10. The highest coercivity of 624 kA·m−1 is obtained for ellipsoid nanowires with a mean length of 200 nm, which also displays a strong magnetic anisotropy. As a result, the highest energy product of the wires reaches 248 kJ·m−3.
KeywordsCo nanowires Morphology control Tip shape High energy product
This work was financially supported by the National Natural Science Foundation of China (Nos. 51401001, 51371011, 51331003), the International S&T Cooperation Program of China (No. 2015DFG52020).
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