Room-temperature ferromagnetic Zn1−xNi x S nanoparticles
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Nickel-doped zinc sulfide nanoparticles (Zn1−xNi x S) at x = 0.00, 0.02, 0.05, 0.08 and 0.10 were synthesized by solid-state reaction. The (nickel sulfide) NiS and (zinc sulfide) ZnS nanoparticles in desired ratios were taken, mixed and ground for 6 h at a speed rate of 300 rpm using a planetary ball mill. The milled nanoparticles were sintered at 600 °C for 8 h using a high-temperature vacuum furnace. The structural, optical, luminescence and magnetic properties of the Zn1−xNi x S nanoparticles were characterized by powder X-ray diffraction (XRD), UV–Vis–NIR diffuse reflectance spectroscopy, photoluminescence (PL) spectroscopy and vibrating sample magnetometer (VSM). No change in crystal structure was observed from XRD by substitution of Ni into ZnS lattice. The mean crystallite size was found to be 37 nm. The band gap of Zn1−xNi x S nanoparticles decreased from 3.57 to 3.37 eV on increasing the dopant concentration. The room-temperature photoluminescence (PL) spectra of Zn1−xNi x S nanoparticles showed two broad and intense emission peaks at 420 and 438 nm with excitation wavelength of 330 nm. The Zn1−xNi x S nanoparticles showed ferromagnetism at 100 K and at room temperature (300 K) and also the strength of magnetization increased with Ni concentration. The maximum magnetization value of 0.18 emu/g was observed for x = 0.10 at 100 K. The strength of the magnetization observed at 100 K was higher than that of magnetization observed at 300 K.
The authors are highly thankful to VIT-SIF for providing XRD, PL and DRS facilities to carry out the present work. Further authors are also thankful to Dr. G. Venugopal Rao, IGCAR, Kalpakkam, for providing the vibrating sample magnetometer facilities.
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