Magnetic structure and internal field nuclear magnetic resonance of cobalt nanowires
Magnetic structure and internal field nuclear magnetic resonance of cobalt nanowires
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DOI：
10.1039/d1cp05164d
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发表时间：
2022-04-29
影响因子：
3.3
通讯作者：
de Lacaillerie, Jean-Baptiste D'espinose
中科院分区：
文献类型：
--
作者：
Scholzen, Pascal;Lang, Guillaume;de Lacaillerie, Jean-Baptiste D'espinose
通过电沉积在多孔膜中生长的钴金属纳米线的磁性在很大程度上取决于合成条件。在这里，我们重点研究电解质添加剂对电沉积纳米线磁各向异性的作用。通过磁力测定和内场核磁共振 (IF NMR) 研究，我们比较了在存在或不存在有机添加剂的情况下合成的 50 和 200 nm 直径 Co 纳米线的磁性和晶体结构。将 IF NMR 的光谱特征与 X 射线衍射图进行结构比较，并将铁磁多畴结构中 NMR 增强因子的各向异性与磁力测定结果进行比较。正如预期的那样，50 nm 纳米线的磁性行为主要由磁畴沿轴定向的形状各向异性决定，但 200 nm 纳米线的分析被证明更为复杂。 Co-59 IF NMR 显示，在存在或不存在有机添加剂的情况下电沉积样品之间的决定性差异不是主要的结晶系统（fcc 或 hcp），而是相干域的尺寸和边界。低于 210 MHz 的共振表明，在存在有机添加剂的情况下，钴晶域较小，并且晶界有缺陷。这阻止了样品的 Co hcp 部分出现在不存在有机添加剂的情况下观察到的强磁晶各向异性。在有机添加剂存在下，即使在宽达 200 nm 的纳米线中，磁性行为仍然由形状各向异性决定，具有正的有效磁各向异性和 NMR 增强因子的强各向异性。
The magnetic properties of cobalt metal nanowires grown by electrodeposition in porous membranes depend largely on the synthesis conditions. Here, we focus on the role of electrolyte additives on the magnetic anisotropy of the electrodeposited nanowires. Through magnetometry and internal field nuclear magnetic resonance (IF NMR) studies, we compared both the magnetic and crystalline structures of 50 and 200 nm diameter Co nanowires synthesized in the presence or absence of organic additives. The spectral characteristics of IF NMR were compared structurally to X-ray diffraction patterns, and the anisotropy of the NMR enhancement factor in ferromagnetic multidomain structures to magnetometry results. While the magnetic behavior of the 50 nm nanowires was dominated, as expected, by shape anisotropy with magnetic domains oriented on axis, the analysis of the 200 nm proved to be more complex. Co-59 IF NMR revealed that the determining difference between the samples electrodeposited in the presence or in absence of organic additives was not the dominant crystalline system (fcc or hcp) but the coherent domain sizes and boundaries. In the presence of organic additives, the cobalt crystal domains are smaller and with defective grain boundaries, as revealed by resonances below 210 MHz. This prevented the development in the Co hcp part of the sample of the strong magnetocrystalline anisotropy that was observed in the absence of organic additives. In the presence of organic additives, even in nanowires as wide as 200 nm, the magnetic behavior remained determined by the shape anisotropy with a positive effective magnetic anisotropy and strong anisotropy of the NMR enhancement factor.