Interface-induced d0 ferromagnetism in undoped ZnO thin films grown on different oriented sapphire substrates
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The origin of d0 ferromagnetism in ZnO material still remains an open question. Here, we report a systematic study of the structural, optical, Raman and magnetic properties of undoped ZnO films grown on a-, c-, m- and r-plane sapphire substrates by radio frequency magnetron sputtering at room temperature. It is found that the polarity of the substrate does not affect the preferential growth of undoped ZnO film along the c-axis, but it will obviously affect the species and concentration of intrinsic defects in films, thereby regulating the optical and Raman properties of undoped ZnO films. Magnetic measurement reveals that all undoped ZnO films exhibit clear hysteresis loops at room temperature, confirming the presence of room temperature ferromagnetism. Furthermore, the relationship between intrinsic defects and magnetic properties was discussed, which suggests that the observed ferromagnetic order has nothing to do with the internal intrinsic defects in undoped ZnO films, but is derived from the interface effects between the undoped ZnO films and the substrates.
The authors gratefully acknowledge support from the National Natural Science Foundation of China (Grant No. 51472038), the Natural Science Foundation of Chongqing (Grant Nos. cstc2016jcyjA0390, cstc2018jcyjA2923), the Science and Technology Research Project of Chongqing Education Committee (Grant No. KJ1500319), the Foundation for the Creative Research Groups of Higher Education of Chongqing (Grant No. CXTDX201601016).
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