An ac susceptibility study in capped Ni/Ni(OH)2 coreshell nanoassemblies: dual peak observations

Jeffrey F Godsell (1) , Tanushree Bala (2) , Kevin M Ryan (2) , Saibal Roy (1)

1 Microsystems Centre
2 The Department of Chemical and Environmental Sciences

14 In the present study, the AC susceptibility (χànd χ'') variation with 15 temperature (10-100K) for oleic acid capped Ni/Ni(OH) 2 core/shell nanoparticle 16 assemblies are reported at frequencies varying from 0.1 Hz to 1000 Hz. Nanoparticle 17 assemblies, with two average particle diameters of ~34 nm and ~14 nm were 18 synthesised using a wet chemical synthesis approach. Two peaks in the AC 19 susceptibility versus temperature curves are clearly discernable for each of the 20 samples. The first, occurring at ~22K was attributed to the 21 paramagnetic/antiferromagnetic transition of the Ni(OH) 2 present in the shell. The 22 second higher temperature peak was attributed to the superparamagnetic blocking of 23 the pure Ni situated at the core of the nanoparticles. The higher temperature peaks in 24 both the χànd χ'urves were observed to increase with increasing frequency. Thus 25 2 the Néel and the blocking temperatures for such core-shell nano-assemblies were 26 clearly identified from the AC analysis, where as they were not discernable 27 (superimposed) even from very low DC (FC/ZFC) field measurements. Interparticle 28 interactions within the assemblies were studied through the fitting of 29 phenomenological laws to the experimental datasets. It is observed that even with an 30 oleic acid capping layer, larger Ni/Ni(OH) 2 nanoparticles experience a greater degree 31 of sub-capping layer oxidation thus producing lower magnetic interaction strengths.

Mots clés: Physical Sciences

Jeffrey F Godsell, Tanushree Bala, Kevin M Ryan, Saibal Roy. An ac susceptibility study in capped Ni/Ni(OH)2 coreshell nanoassemblies: dual peak observations. Journal of Physics D: Applied Physics, 2011, 44 (32), pp.325004. ⟨10.1088/0022-3727/44/32/325004⟩. ⟨hal-00642372⟩