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Magnetic, structural and optical properties measurements of samples S1, S2, S3, S4 and S5 prepared at different P O . (a) M-H curves measured at room temperature with the applied magnetic field parallel to the film surface. (b) XRD patterns and the symbol “*” represents ZnO (101) peak. (c) PL spectra and the symbol “◆”, “#”, “●” and “Δ” represent the red-emission peak, removed frequency-doubled laser, green-emssion peak and UV-emission shoulder, respectively. (d) ESR spectra recorded at 270 K in a dark chamber and the symbol “□” represents the shallow donor state resonance peak.
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Schematic diagram of ferromagnetic mechanism for ionized VZn embedded in Cu-doped ZnO system. White circles, black circles, green rhombus, blue triangles, red square and large olive circles represent zinc atoms, Cu2+ cations, Cu3+ cations, neutral defects, ionized defect and interaction range of ionized zinc vacancy, respectively. Oxygen atoms are not shown here.
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This paper reports the origin of ferromagnetism in Cu-doped ZnOthin films. Room-temperature ferromagnetism is obtained in all the thin films when deposited at different oxygen partial pressure. An obviously enhanced peak corresponding to zincvacancy is observed in the photoluminescence spectra, while the electrical spin resonance measurement implies the zincvacancy is negative charged. After excluding the possibility of direct exchange mechanisms (via free carriers), we tentatively propose a quasi-indirect exchange model (via ionized zincvacancy) for Cu-doped ZnO system.
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