镍超细微颗粒的核磁共振研究

报导了对镍超细微颗粒进行核磁共振研究的初步结果通过测量６１Ｎｉ的零场核磁共振谱研究镍超细微颗粒的赵精细磁场的分布．微颗粒平均直径约２０ｎｍ．为了对比，还对镍粉（粒径约７６μｍ）进行了类似测量．发现微颗粒与块状样品的核磁共振谱的共振峰位置基本相同，但在线型、谱宽和信噪比方面明显不同。这表明其超精细磁场的分布有特征性的区别．镍超细微颗粒的共振谱比块状样品稍微展宽．因为超细微颗粒的表面原子数目比块状样品的多，谱线变宽可能与超细微颗粒的表面效应有关。

NMR INVESTIGATION OF NICKEL ULTRAFINE PARTICLES

The hyperfine field distribution in nickel ultrafine particles, having averagesize of about 20 nm, was investigated by measuring the 61Ni NM R (nuclear magnetic resonance) spectrum at zero applied field at room temperature. As a counterpart, a similarmeasurement was made on the sample of bulk nickel which is powder having average sizeof 76 micron. The 61Ni resonance peak in the sample of unenriched nickel ultrafine particles is observed at a frequency of about 26.2 MHz, which means that the hyperfine field isthe order of about 6.89 T, almost the same as that in unenriched bulk nickel samples inwhich the 61Ni resonance is about 26.14 MHz. In addition to the change of lineshape whichis deviated from the Gaussian, the 61Ni resonance spectrum in the nickel ultrafine particlesis broadened significantly compared with that in nickel bulk sample. The NOR data indicate clearly that the hyperfine field in nickel ultra fine particle has wider distribution thanthat in bulk sample.It can be understood by considering the fact that the number of thesurface atoms in ultrafine particles is large in contrast to the bulk. The broad nature mustbe associated with the surface effect of nickel ultrafine particles. Since the environment ofan atom located at the surface of nickel particles is different from that in the interior,whichcauses the variations of the hyperfine interactions in different regions, there exists distribution of hyperfine field even in a particle. It had been determined that the lower and higherfrequency side of 61Ni NMR spectrum at zero applied field corresponds to resonance signals from surface and interior part in the nickel ultra fine particles,respectively. Thehyperfine field decreases gradually from interior to the surface.