Vacancy-Induced Ferromagnetism in SnO2 Nanocrystals: A Positron Annihilation Study
CHEN Zhi-Yuan1,2, CHEN Zhi-Quan2**, PAN Rui-Kun3, WANG Shao-Jie2**
1School of Nuclear Technology and Chemistry and Biology, Hubei University of Science and Technology, Xianning 437100 2Hubei Nuclear Solid Physics Key Laboratory, Department of Physics, Wuhan University, Wuhan 430072 3School of Materials Science and Engineering, Hubei University, Wuhan 430062
Abstract：SnO2 nanopowders were pressed into pellets and annealed in air from 100 to 1400°C. Both XRD and Raman spectroscopy confirm that all annealed samples were single phase with a tetragonal rutile structure. Annealing induces an increase in the SnO2 grain size from 30 to 83 nm. Positron annihilation measurements reveal vacancy defects in the grain boundary region, and the interfacial defects remain stable after annealing below 400°C, then they are gradually recovered with increasing annealing temperature up to 1200°C. Room temperature ferromagnetism was observed for SnO2 nanocrystals annealed below 1200°C, and the magnetization decreases continuously with increasing annealing temperature. However, the ferromagnetism disappears at 1200°C annealing. This shows good coincidence with the recovery of interfacial defects in the nanocrystals, suggesting that the ferromagnetism is probably induced by vacancy defects in the interface region.
2013, Vol. 30 
