Nanoparticles samples of pure SnO2, Sn0.99Mn0.01O2, Sn0.98Mn0.02O2, Sn0.98Mn0.01Fe0.01O2, Sn0.96Mn0.02Fe0.02O2, Sn0.98Mn0.01Co0.01O2 and Sn0.96Mn0.02Co0.02O2 were synthesized by sol-gel method. X-ray diffraction analysis and Fourier transform infrared spectra of all prepared samples confirmed the formation of single phase SnO2 with tetragonal rutile structure. The average crystallite sizes of the prepared samples were estimated to be in the range of 7–12 nm. Energy-dispersive X-ray spectroscopy analysis of Sn0.98Mn0.02O2, Sn0.96Mn0.02Fe0.02O2, and Sn0.96Mn0.02Co0.02O2 samples evidently proved the existence of Mn, Fe, Co, Sn, and O elements only without any impurity, indicating the high purity of the prepared samples. Transmission electron microscopy images showed the formation of ultra-fine spherical nanoparticles in all samples with average particles sizes of 8.5–15 nm. From the UV–Vis absorption spectra results, the band gap energy value of the pure SnO2 nanoparticles was estimated to be 3.90 eV and it varied with dopant type and its concentration. Room temperature magnetic hysteresis loops of all samples exhibited ferromagnetic behavior. Clear enhancement in the room temperature ferromagnetism was achieved in pure SnO2 nanoparticles after doping with Mn and codoping with (Mn, Fe) or (Mn, Co) dopants. The maximum value of the saturation magnetization was found in Sn0.96Mn0.02Fe0.02O sample, while Sn0.96Mn0.02Co0.02O sample displayed the higher values of coercivity and retentivity.
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