Magnetization and magnetoresistance of ZnO thin film

A ZnO film was deposited on a silicon wafer by magnetron sputtering, and the magnetic and the electronic properties have been studied. The magnetic property measurements show that the ZnO film is ferromagnetic at room temperature. The magnetoresistance (\textit{MR}) measurement reveals a positive \textit{MR} of 23.3{\%} at 2 K, which is due to the spin splitting induced by the \textit{sd} exchange interaction. Aging effect, however, was observed when the sample was put under the air for a month. The ferromagnetism disappears and the \textit{MR} becomes negative, too. It is explained by the modification of the defects in ZnO. The huge magnitude of the spin-dependent \textit{MR} as well as the aging effect of \textit{MR} demonstrates that the observed ferromagnetism in ZnO is intrinsic, not from impurity or contamination.