Influence of magnetic ion doping on structural, optical, magnetic and hyperfine properties of nanocrystalline SnO_2 based dilute magnetic semiconductors

摘要

This article reports the structural, optical and magnetic properties of transition metal (Ni, Co, Mn and Fe) doped SnO_2 nanoparticles prepared by modified Pechini sol-gel method. From the X-ray diffraction studies, it is obvious that all the synthesized samples show a phase purity of rutile tetragonal crystal structure of SnO_2. The morphology was studied and the particle sizes were estimated from the field emission scanning electron microscopy. From photoluminescence spectra, we observed emission due to the presence of singly ionized oxygen vacancies. Raman spectroscopy shows dominant peaks at 644 and 782 cm~(-1) which were ascribed to A_(1g) and B_(2g) modes of the rutile structure. Isomer shifting due to dopant addition and large quadrupole splitting due to surface defects were observed in Mossbauer spectra. All the samples show ferromagnetic ordering up to 1 T. The relatively stronger ferromagnetic nature in Fe and Co doped SnO_2 is due to the strong p-d exchange interaction. In case of Ni and Mn doped SnO_2 samples, the lack of carrier-mediated interaction due to its inherent semiconducting nature reduces the total magnetic moment observed in these samples. The exchange coupling depends on the dopant type and its concentration.