Abstract
Ferromagnetism was observed at room temperature in monodisperse CeO2 nanospheres synthesized by hydrothermal treatment of Ce(NO3)3·6H2O using polyvinylpyrrolidone as a surfactant. The structure and morphology of the products were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and field-emission scanning electron microscopy (FE-SEM). The optical properties of the nanospheres were determined using UV and visible spectroscopy and photoluminescence (PL). The valence states of Ce ions were also determined using X-ray absorption near edge spectroscopy. The XRD results indicated that the synthesized samples had a cubic structure with a crystallite size in the range of approximately 9 to 19 nm. FE-SEM micrographs showed that the samples had a spherical morphology with a particle size in the range of approximately 100 to 250 nm. The samples also showed a strong UV absorption and room temperature PL. The emission might be due to charge transfer transitions from the 4f band to the valence band of the oxide. The magnetic properties of the samples were studied using a vibrating sample magnetometer. The samples exhibited room temperature ferromagnetism with a small magnetization of approximately 0.0026 to 0.016 emu/g at 10 kOe. Our results indicate that oxygen vacancies could be involved in the ferromagnetic exchange, and the possible mechanism of formation was discussed based on the experimental results.
Highlights
Oxide-dilute magnetic semiconductors (O-DMSs) such as ZnO, TiO2, SnO2, and In2O3 doped with transition metal (TM) ions have recently attracted much attention due to their potential use in magneto-optoelectronic applications [1,2,3]
We report the ferromagnetism observed in monodisperse CeO2 nanospheres with a particle size of approximately 200 nm synthesized by hydrothermal treatment of Ce(NO3)3Á6H2O using polyvinylpyrrolidone (PVP) as a surfactant
The sample obtained with CeCl3Á7H2O as the starting agent shows no X-ray diffraction (XRD) peaks, indicating that it is amorphous, whereas the sample from Ce(NO3)3Á6H2O exhibits XRD peaks that correspond to the (111), (200), (220), (311), (222), and (400) planes, which are consistent with the face-centered cubic fluorite structure of CeO2 in the standard data from the Joint Committee on Powder Diffraction Standards (JCPDS) 34–0394, indicating that pure CeO2 was successfully synthesized via these procedures
Summary
Oxide-dilute magnetic semiconductors (O-DMSs) such as ZnO, TiO2, SnO2, and In2O3 doped with transition metal (TM) ions have recently attracted much attention due to their potential use in magneto-optoelectronic applications [1,2,3]. Tiwari et al [4] firstly discovered room temperature ferromagnetism (RT-FM) in Ce1−xCoxO2−δ (x ≤ 0.05) films deposited on a LaAlO3 (001) substrate by pulsed laser deposition (PLD) technique These films are transparent in a visible regime and exhibit a very high Curie temperature (TC) at approximately 740 to 875 K with large magnetic moments of 6.1 ± 0.2 to 8.2 ± 0.2 μB/Co. Following the work by Tiwari et al, Song et al [5] reported successful fabrication ofCe1−xCoxO2−δ (x = 0.03) thin films with (111) preferential orientation deposited on a Si (111) substrate by a PLD technique. The authors suggested that the RT-FM originated from an exchange of F-center, which involved a combination of oxygen vacancies and TM doping
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