High blocking temperature in SnO2 based super-paramagnetic diluted magnetic semiconductor

(Fe,Cu)-doped SnO2 nanocrystals was synthesized using the co-precipitation method. Magnetic Properties Measurement System (MPMS) revealed that for simple doping, Fe-doped SnO2 soft ferromagnetism at low temperature appears, while the ferromagnetic phase is stable at temperature higher than room temperature for Cu co-doping element. The ferromagnetism is significantly enhanced by the Cu addition to Fe-doped SnO2, according to the ZFC and FC magnetizations and the hysteresis loops. The evidences for the existence of superparamagnetism are characterized and high blocking temperature super-paramagnetism in (Fe,Cu)-doped SnO2 nanocrystals was observed. Based on first-principles calculations, we have investigated electronic structures and magnetic properties of Fe-doped SnO2 and (Fe,Cu)-doped SnO2 with and without defect with LDA and LDA-SIC approximations. The results suggest that the oxygen vacancies (VO) play a critical role in the activation of ferromagnetism in Fe doped SnO2. For (Fe,Cu)-doped SnO2 the results exhibit that Cu strongly influences on the magnetic properties of these doped systems which are in good agreement with the experimental observations. Electronic structure show that the presence of Cu promote the ferromagnetic bound magnetic polaron interaction through the carriers introduce by d (Cu).