Size Dependence of Defect-Induced Room Temperature Ferromagnetism in Undoped ZnO Nanoparticles

Abstract

We report the intrinsic room-temperature ferromagnetism in undoped ZnO nanoparticles with different sizes synthesized by a wet chemical method at different temperatures. Electron paramagnetic resonance, X-ray photoelectron spectroscopy, and photoluminescence measurements demonstrate clearly the singly charged oxygen vacancies are the main defects, and the relative occupancy of that decreases with increasing sizes and annealing temperatures. Importantly, a direct correlation between the ferromagnetism and the relative concentration of the singly charged oxygen vacancies is established, which suggests that the singly charged oxygen vacancies play a crucial role in modulating ferromagnetic behaviors. Moreover, the size-dependent ferromagnetism can be manipulated conveniently by changing of the surface–volume ratio, which is in favor of future electronic and spintronic application.

Brush-like SnO2/ZnO hierarchical nanostructure: Synthesis, characterization and application in UV photoresponse

“…The binding energy splitting of Zn 2p is 23 eV which agrees with the result of Zn 2+ in ZnO. 40 The typical O1s peak of the brush-like nanostructure is located at 530 eV which can be deconvoluted into two Gaussian peaks at 529.9 and 531.0 eV, as shown in Figure 4(d). The low binding energy at 529.9 eV correspond to O 2− in the regular structure of wurtzite ZnO matrix, and the high binding energy peak at 531.0 eV is attributed to oxygen deficient state.…”

“…The low binding energy at 529.9 eV correspond to O 2− in the regular structure of wurtzite ZnO matrix, and the high binding energy peak at 531.0 eV is attributed to oxygen deficient state. [40][41][42] The optical properties of the SnO 2 nanowires and SnO 2 /ZnO hierarchical structures were investigated by photoluminescence spectrometer. Figure 5(a) shows the PL spectrum of the SnO 2 nanowires excited by 280 nm line from a Xe lamp, a broad emission band can be observed, which is deconvocated into two emission bands centered at 361 nm (3.43 eV) and 445 nm (2.78 eV).…”

Controllable fabrication and optical properties of Sn-doped ZnO hexagonal microdisk for whispering gallery mode microlaser

“…The reduction of electron charge density in the oxygen vacancy area results in less screening of the O 2− 1s electrons from their nucleus, this increases the effective nuclear charge and the binding energy of O 2− 1s electron, so the peak at 531.0 eV is attributed to oxygen deficient state. 34,35 To confirm the state of the oxygen vacancy, the EPR spectrum(g = 1.96) of the ZnO:Sn microdisks is shown in Figure 4(c), the characteristics of ferromagnetism indicates the states of paramagnetic oxygen vacancies with unpaired singly electron (V O+ ) in the ZnO:Sn microdisks. 31,34 So the green emission band from the ZnO:Sn microdisks is attributed to the singly charged oxygen vacancy defects, this result is similar to the defect emission mechanism of the undoped ZnO micro/nanostructures.…”

ZnO-based nanostructures for diluted magnetic semiconductor

“…Based on the EPR and XRS results, the singly charged oxygen vacancies V + O located near the surface were suggested as the main defects that contribute to the RTFM ordering. More recently, a study on ZnO nanoparticles reported similar results regarding the role of V + O [59]. More interestingly, the relative concentration of V + O in both studies can be tuned by the size of the nanoparticles and annealing conditions.…”

“…In the XPS spectrum of the Zn 2p core level, the peak positions of Zn 2p3/2 and Zn 2p1/2 are normally located at 1021.9 and 1045 eV, respectively. A spin-orbital splitting of 23.1 eV can be used to confirm that Zn is present as Zn 2+ [59].…”