科研之友
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摘要
In this study, the ac susceptibility (chi' and chi '') variation with temperature (10-100 K) for oleic acid (OA) capped Ni/Ni(OH)(2) core-shell nanoparticle assemblies are reported at frequencies varying from 0.1 to 1000 Hz. Nanoparticle assemblies, with two average particle diameters of similar to 34 nm and similar to 14 nm, were synthesized using a wet chemical synthesis approach. Two peaks in the ac susceptibility versus temperature curves are clearly discernable for each of the samples. The first, occurring at similar to 22K was attributed to the paramagnetic/antiferromagnetic transition of the Ni(OH)(2) present in the shell. The second higher temperature peak was attributed to the superparamagnetic blocking of the pure Ni situated at the core of the nanoparticles. The higher temperature peaks in both the chi' and chi '' curves were observed to increase with increasing frequency. Thus the Neel and the blocking temperatures for such core-shell nanoassemblies were clearly identified from the ac analysis, whereas they were not discernible (superimposed) even from very low dc (FC/ZFC) field measurements. Interparticle interactions within the assemblies were studied through the fitting of phenomenological laws to the experimental datasets. It is observed that even with an OA capping layer, larger Ni/Ni(OH)(2) nanoparticles experience a greater degree of sub-capping layer oxidation thus producing lower magnetic interaction strengths.
- 出版日期2011-8-17
