EFFECTS OF DEFECTS ON MAGNETORESISTIVITY IN LA0.7SR0.3MNO3

The effects of structural and oxygen site defects on the ferromagnetic phase transition and magnetotransport in doped lanthanum manganite fi lms have been examined. Oxygen defects were introduced through a vacuu m annealing process while structural defects were introduced using ion irradiation. The introduction of both defect types strongly suppresse d the Curie temperature T-c while increasing the peak resistivity, act ivation energy, and magnetoresistance ratio. For defect types leading to similar reductions in T-c, structural defects lead to a broader tra nsition regime and a smaller MRR than are found for oxygen defects. We ll above T-c both defect types lead to nearly identical resistivity cu rves. Structural defects are argued to primarily affect the carrier mo bility, hence these data provide a clue that the carrier mobility is d ominating the transport properties in this regime.