Pure metallic copper nanoparticles free of any substrate were synthesized by the thermo-chemical reduction of copper acetate using triethanolamine as a reducing-cum-protection agent. The structure and physical and magnetic properties of the Cu NPs were analysed physicochemically. Microscopic analysis reveals the formation of particles of size of 3–5 nm as seen by TEM but present as a large agglomeration as identified by SEM. A structure of Cu₉ is predicted for the Cu NPs on the basis of investigations using XPS, MALDI, EPR, and magnetic measurements and supported by the prediction of DFT calculation from an earlier work. The most important findings come from magnetization studies which prove the existence of giant diamagnetism from the nanomer clusters of copper as well as the formation of two different ferromagnetic transitions at ∼40 K and ∼100 K, the latter two arising from the surface properties possibly due to thin films of CuO and/or the presence of TEOA giving rise to temperature dependent coercivity revealing them to be soft room temperature ferromagnets. The clusters of Cu NPs with the identified structure show temperature and field dependent giant diamagnetism which is about 29–39 times larger than the diamagnetism calculated from known and established atomic values. Though such enhanced diamagnetism has been predicted for noble metal clusters, experimental observation so far has been restricted to Au and Pt and this is probably the first report on substrate-free metallic copper clusters.

中文翻译：

---

无基材的铜纳米团簇具有超强的反磁性和基于表面的软铁磁性

使用三乙醇胺作为还原兼保护剂，通过乙酸铜的热化学还原反应合成了不含任何底物的纯金属铜纳米粒子。物理化学分析了铜纳米颗粒的结构和物理磁性能。显微分析表明，TEM观察发现形成了3–5 nm的颗粒，而SEM则表明存在大的团聚。Cu ₉的结构在使用XPS，MALDI，EPR和磁测量的研究基础上，对Cu NPs进行了预测，并得到了早期工作中对DFT计算的预测的支持。最重要的发现来自磁化研究，这些研究证明了铜的纳米单体簇存在巨大的反磁性，并且在〜40 K和〜100 K处形成了两个不同的铁磁跃迁，后两个是由于表面性质而引起的CuO薄膜和/或TEOA的存在会引起温度相关的矫顽力，这表明它们是柔软的室温铁磁体。具有确定结构的Cu NPs团簇显示出与温度和磁场有关的巨型反磁性，比根据已知和确定的原子值计算出的反磁性大29-39倍。