Abstract
In this paper, we report the existence of defect induced intrinsic room-temperature ferromagnetism (RTFM) in Cu doped ZnO synthesized via a facile sol–gel route. The wurtzite crystal structure of ZnO remained intact up to certain Cu doping concentrations under the present synthesis environment as confirmed by the Rietveld refined X-ray diffraction pattern with the average crystallite size between 35 and 50 nm. Field emission scanning electron microscopy reveals the formation of bullet-like morphologies for pure and Cu doped ZnO. Diffuse reflectance UV-vis shows a decrease in the energy band gap of ZnO on Cu doping. Further, these ZnO samples exhibit strong visible photoluminescence in the region of 500–700 nm associated with defects/vacancies. Near-edge X-ray absorption fine-structure measurements at Zn, Cu L3,2- and O K-edges ruled out the existence of metallic Cu clusters in the synthesized samples (up to 2% doping concentration) supporting the XRD results and providing the evidence of oxygen vacancy mediated ferromagnetism in Cu : ZnO systems. The observed RTFM in Cu doped ZnO nanostructures can be explained by polaronic percolation of bound magnetic polarons formed by oxygen vacancies. Further, extended X-ray absorption fine-structure data at Zn and Cu K-edges provide the local electronic structure information around the absorbing (Zn) atom. The above findings for ZnO nanostructures unwind the cause of magnetism and constitute a significant lift towards realizing spin-related devices and optoelectronic applications.
Highlights
The conjunction of spin and charge states of an electron will be helpful in manufacturing low power consumption and fast processing devices
We report the existence of defect induced intrinsic room-temperature ferromagnetism (RTFM) in Cu doped ZnO synthesized via a facile sol–gel route
FM is due to the exchange interaction between Co (d) electrons and free carriers generated due to Co-doping FM is attributed to oxygen vacancies Antiferromagnetic coupling between Co ions at higher magnetic elds Weak FM at 300 K, FM due to oxygen and/or Zn vacancies Annealed samples show FM, Mn–H– Mn bridge structure and the Mn– Mn exchange interaction Intrinsic FM due VO and/or defects FM is due to bound magnetic polaron (BMP) interactions mediated through oxygen vacancies FM is defect mediated by exchange interaction of oxygen vacancies and Fe ions Overlapping of bound magnetic polarons (BMPs) causes the alignment of their spins, resulting in long-range ferromagnetic order FM due to oxygen vacancies associated with the BMP model
Summary
The conjunction of spin and charge states of an electron will be helpful in manufacturing low power consumption and fast processing devices. In the vicinity of Cu, the intensity of deep emission levels in ZnO increases.[35] Cu doped ZnO as a DMS is supposed to have a longer coherence time which provides an opportunity for increasing the spin lifetime for practical spintronics applications.[36] the literature states that the doped transition metal ion can change the magnetic properties of ZnO.[37,38] the effect of doping is still complicated to understand. The surface effect and the growth of nanostructures under given synthesis conditions induce defects in the material and oxide based DMSs usually show different magnetic behavior.[39] based on the experimental results and theoretical calculations, this paper studies the in uence of Cu doping on electronic structure and magnetic properties of ZnO. The results obtained and their discussion unwind the cause of magnetism and prove ZnO to be a DMS having potential in spintronics and optoelectronic applications
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