Observation of Room Temperature Ferromagnetism in Conducting and Insulating Cu doped ZnO Thin Films
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With pulsed laser deposition, the Cu0.04Zn0.96O thin films are grown at 600 °C under three different oxygen pressures, namely PO2 = 0.00, 0.02, and 1.00 Pa. X-ray diffraction shows single-phase material for the samples grown under PO2 = 0.00 and 1.00 Pa and CuO secondary phase for the PO2 = 0.02 Pa grown sample. The observation of satellite structures in the Cu 2p core level X-ray photoelectron spectroscopy (XPS) spectra suggest the presence of Cu2+ and CuO secondary phases in the samples grown at PO2 = 0.02 and 1.00 Pa. The sample grown under vacuum (PO2 = 0.00 Pa) shows mixed Cu oxidation state of 1 + or 2 + . The sample grown without oxygen is n-type and those grown with oxygen are highly insulating. The insulating sample grown at PO2 = 0.02 Pa shows highest magnetization due to possible collective behavior of Cu2+ – O v – Cu2+ network in the form of bound magnetic polaron (BMP) and ferromagnetic superexchange interaction coming from uncompensated surface spins of the Cu ions in the CuO secondary phase. Both delocalized electrons (∼3.32 × 1018) due to oxygen deficient defects and reduced amount of effective Cu2+ ions discredit the BMP model for this vacuum grown sample, and magnetism is suggested due to O v and presence of possible CuO secondary phase.
KeywordsDiluted mgnetic semiconductor Cu doped ZnO Thin films XPS Magnetization Secondary phase
The work presented here was supported by the RGC, HKSAR under the GRF (HKU703612P) and SEG HKUST03, as well as HKU Seed Funding Program for Basic Research (201111159037), and the National Natural Science Foundation of China (No. 61205037), the China Postdoctoral Science Foundation funded project (No. 2013M531862) and the Research Fund for the Doctoral Program of Higher Education of China (No. 20124407120017).
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