Controlled grain-boundary defect formation and its role in the high-Tc ferromagnetism of Ni2+:SnO2

Understanding the roles of defects in the ferromagnetism of oxide diluted magnetic semiconductors is a central challenge in the field of magnetism. In this paper, we report a systematic study of the activation and deactivation of high-T-c (> 300 K) ferromagnetism in Ni2+:SnO2 by gentle annealing at 100 degrees C. We attribute this activation and deactivation to the generation and passivation of nonstoichiometric grain-boundary defects, respectively. (C) 2006 American Institute of Physics.