• N S Gajbhiye

      Articles written in Pramana – Journal of Physics

    • Re-dispersible Li+ and Eu3+ co-doped CdS nanoparticles: Luminescence studies

      N S Gajbhiye Raghumani Singh Ninghoujam Asar Ahmed D K Panda S S Umare S J Sharma

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      Re-dispersible CdS, 5 at.% Eu3+-doped CdS, 2 at.% Li+ and 5 at.% Eu3+ co-doped CdS nanoparticles in organic solvent are prepared by urea hydrolysis in ethylene glycol medium at a low temperature of 170°C. CdS nanoparticles have spherical shape with a diameter of $\sim 80$ nm. The asymmetric ratio ($A_{21}$) of the integrated intensities of the electrical dipole transition to the magnetic dipole transition for 5 at.% Eu3+-doped CdS is found to be 3.8 and this ratio is significantly decreased for 2 at.% Li+ and 5 at.% Eu3+ co-doped CdS ($A_{21} = 2.6$). It establishes that the symmetry environment of Eu3+ ion is more favored by Li-doping. Extra peak at 550 nm (green emission) could be seen for 2 and 5 at.% Eu3+ co-doped CdS. Also, the significant energy transfer from host CdS to Eu3+ is found for 5 at.% Eu3+-doped CdS compared to that for 2 at.% Li+ and 5 at.% Eu3+ co-doped CdS.

    • Observation of exchange bias and spin-glass-like ordering in 𝜀-Fe2.8Cr0.2N nanoparticles

      N S Gajbhiye Sayan Bhattacharyya Sachil Sharma

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      Nanoparticles of 𝜀-Fe2.8Cr0.2N system exhibit the exchange bias phenomenon due to the exchange coupling of the spins of the antiferromagnetic (AF) oxide/oxynitride surface layer and the ferromagnetic (FM) nitride core. Exchange bias is observed at 10 K both in the absence and presence of cooling field. Due to the interface disorder, a mixture of parallel and anti-parallel/perpendicular coupling of the AF and FM spins is observed. The roughness of AF-FM interface induces disorder due to the random exchange anisotropy. The saturation magnetization is also found to be drastically lowered as compared to parent 𝜀-Fe3N. Below 58 K, the broad peak ($T_{E} \cong T_{f}$) in zero-field cooled (ZFC) magnetization curves indicates the presence of unidirectional anisotropy and spin-glass-like ordering, that arises from the freezing of localized frustrated spins.

    • Reduction mechanism of Ni2+ into Ni nanoparticles prepared from different precursors: Magnetic studies

      R S Ningthoujam N S Gajbhiye Sachil Sharma

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      The reduction mechanism of Ni2+ into Ni particles using different precursors such as NiCl2 solution, NiO powder and Ni[(NH3)6]Cl2 complex has been established. Different particle sizes can be designed from these precursors. The smallest crystallite size (12 nm) can be obtained from Ni[(NH3)6]Cl2 complex in the presence of the stabilizing ligand (oleic acid). The field-cooled (FC) and zero-field-cooled (ZFC) magnetization of Ni particles obtained from Ni[(NH3)6]Cl2 complex in the temperature range 5–300 K established the ferromagnetic interaction up to 300 K. The magnetization values at three different temperatures 5, 70 and 300 K are 50.2, 49.5 and 45.5 Oe respectively at $3 \times 10^{4}$ Oe applied field and such values are less than that of the bulk value. The Curie temperature $(T_{c})$ decreases slightly with the decrease of particle size. This study will provide guidance in the preparation of metal nanoparticles from different precursors.

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