Defect mediated room temperature ferromagnetism and resistance minima study in epitaxial ZnGa_0.002Al_0.02O transparent conducting oxide films

We report on the micro-structural, transport, optical and magnetic properties in ZnGa_0.002Al_0.02O (AGZO) films grown by pulsed laser deposition under different growth conditions. AGZO films grown at substrate temperatures of 600 °C show metal-like behavior with a resistivity minima at lower temperatures, whereas films grown at 300 °C and ambient oxygen partial pressure of 1 mTorr show metallic nature with resistivity values on the order of 100 µ Ω · cm at room temperature. The most interesting features are the concomitant occurrence of high temperature resistivity minima and room temperature ferromagnetism with a saturation magnetic moment of 1000 A m⁻¹ and with coercivity in the range 100–240 Oe. The temperature dependent resistivity data has been interpreted in the light of quantum corrections to conductivity in disordered systems, suggesting that the e – e interactions is the dominant mechanism in the weak-localization (WL) limit in the case of films showing resisitivity minima. The simultaneous ferromagnetic ordering coupled with the enhancements in electrical conductivity in AGZO system should have their origin in native point defects in the form of oxygen and zinc vacancies and interstitials and their complexes. We propose that formation of oxygen vacancy–zinc interstitial defect complex ( V _O– I _Zn) is responsible for the enhancement in n -type conductivity, and zinc vacancies ( V _Zn) for the observed room temperature ferromagnetism. (paper)