Room temperature dilute magnetism in nanoscale Co and Zn co-doped SnO2

• Undoped SnO2 nanoparticles exhibited diamagnetic behavior at room temperature.
• Co and Zn co-doped SnO2 samples exhibited room temperature ferromagnetism (RTFM).
• Observed RTFM are purely due to intrinsic property and not from secondary phases.
• The origin of observed RTFM might be due to defects induced ferromagnetism.
• All annealed samples exhibited the exchange bias effect.

The influence of Co and Zn co-dopants, crystallite size and annealing temperature on the magnetic and optical properties of SnO2 were investigated. SnO2, Sn0.95Co0.025Zn0.025O2, Sn0.925Co0.05Zn0.025O2, Sn0.925Co0.025Zn0.05O2, Sn0.90Co0.05Zn0.05O2 and Sn0.85Co0.075Zn0.075O2, nanoparticles were synthesized by hydrothermal method. X-ray diffraction and Raman studies confirmed the single phase tetragonal crystal structure for all the investigated samples. The crystallite sizes were estimated to be in the range of 3–8 nm for the as synthesized samples and 20–25 nm for the samples annealed at 800 °C for 2 h. The photoluminescence, Raman and UV–Vis absorption spectroscopy studies revealed the presence of structural defects and possible oxygen vacancies in both the as synthesized and annealed samples. As synthesized undoped SnO2 sample exhibited the diamagnetic behavior at room temperature and all the Co and Zn co-doped samples exhibited the room temperature ferromagnetic (RTFM) behavior. RTFM along with the enhancement of saturation magnetization were observed for all the annealed samples. Interestingly, at room temperature the annealed samples exhibited the exchange bias effect.