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Madhu G, Maniammal K, Biju V. Defect induced ferromagnetic interaction in nanostructured nickel oxide with core-shell magnetic structure: the role of Ni(2+) and O(2-) vacancies. Phys Chem Chem Phys. 2016;18(17):12135-48doi: 10.1039/c5cp03710g.
Madhu, G., Maniammal, K., & Biju, V. (2016). Defect induced ferromagnetic interaction in nanostructured nickel oxide with core-shell magnetic structure: the role of Ni(2+) and O(2-) vacancies. Physical chemistry chemical physics : PCCP, 18(17), 12135-48. https://doi.org/10.1039/c5cp03710g
Madhu, G, et al. "Defect induced ferromagnetic interaction in nanostructured nickel oxide with core-shell magnetic structure: the role of Ni(2+) and O(2-) vacancies." Physical chemistry chemical physics : PCCP vol. 18,17 (2016): 12135-48. doi: https://doi.org/10.1039/c5cp03710g
Madhu G, Maniammal K, Biju V. Defect induced ferromagnetic interaction in nanostructured nickel oxide with core-shell magnetic structure: the role of Ni(2+) and O(2-) vacancies. Phys Chem Chem Phys. 2016 Apr 28;18(17):12135-48. doi: 10.1039/c5cp03710g. PMID: 27074902.
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Phys Chem Chem Phys. 2016 Apr 28;18(17):12135-48. doi: 10.1039/c5cp03710g.

Defect induced ferromagnetic interaction in nanostructured nickel oxide with core-shell magnetic structure: the role of Ni(2+) and O(2-) vacancies.

Physical chemistry chemical physics : PCCP

G Madhu, K Maniammal, V Biju

Affiliations

  1. Department of Physics, University of Kerala, Kariavattom Campus, Thiruvananthapuram, Kerala Pin 695581, India. [email protected] and Department of Physics, University College, Thiruvananthapuram, Kerala Pin 695034, India.
  2. Department of Physics, University of Kerala, Kariavattom Campus, Thiruvananthapuram, Kerala Pin 695581, India. [email protected].

PMID: 27074902 DOI: 10.1039/c5cp03710g

Abstract

Nanostructured nickel oxide samples with crystallite sizes in the range 32-45 nm are synthesized through a facile chemical route using nickel chloride and ethanol amine as the starting materials. The analysis of the antioxidant activity and DC conductivity of the NiO samples confirmed the presence of both Ni(2+) and O(2-) vacancies. The temperature dependent magnetization studies of the samples are done using a Vibrating Sample Magnetometer in the range 20-300 K. The core-shell magnetic structure of the NiO nanoparticles with an antiferromagnetic core and a spin-glass shell is revealed from the zero field cooled and field cooled magnetization studies of the samples. The dependence of uncompensated moments on total spins contradicts Neel's models and is found to vary directly with O(2-) vacancy concentration. The ferromagnetic response of NiO samples due to the interaction between the antiferromagnetic core and the ferromagnetic shell is evident from the magnetic hysteresis studies in the temperature range 20-300 K. The ferromagnetic response is traced to the concentration of O(2-) vacancies, which act as donor impurities and mediate the alignment of magnetic moments associated with Ni(2+) vacancies. The decrease of ferromagnetic contribution upon annealing is explained by the decrease in the concentration of O(2-) vacancies which caused a reduction in the number of magnetic polarons and hence the effective magnetization.

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