Effect of Ni precursor solution concentration on the magnetic properties and exchange bias of Ni-NiO nanoparticulate systems


We report on a comparative study of the exchange bias effect and magnetic properties of Ni-NiO nanoparticulate systems synthesized by the chemical reduction of NiCl2 solution of two different molar concentrations-1 M (high) and 0.05 M (low)-followed by annealing of the dried precipitate in the temperature range 400-600 degrees C in air. Interestingly, the samples derived from the low molarity solution have higher Ni content and larger crystallite size than those prepared from their high molarity counterparts. These molarity dependent features subsequently modulate the magnitude of the exchange bias field in the samples, which is found to be absent or small in the 0.05 M series, but of moderate value in the 1 M samples. The different physical attributes of the particles derived from different concentrations of Ni-precursor solution are explained by invoking different nucleation kinetics and supersaturation degrees surrounding the viable growing nucleus. Furthermore, an observed increase of exchange bias with increasing annealing temperature, in contrast to the reported agglomeration of particles on annealing and subsequent reduction in bias magnitude, has been explained in correlation to the Ni-NiO interface density. (C) 2014 AIP Publishing LLC.



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Roy, A; De Toro, JA; Amaral, VS; Marques, DP; Ferreira, JMF

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A. Roy acknowledges the Foundation of Science and Technology (FCT) of Portugal for financial support under the Grant SFRH/BPD/77574/2011. D. P. Marques acknowledges financial support from the Brazilian CNPQ. Support from CICECO, University of Aveiro, and from the Spanish CICYT [Project MAT2011-26207] is gratefully acknowledged.

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