Desheng Xue

Room temperature ferromagnetism of pure ZnO nanoparticles

We report the room temperature ferromagnetism (RTF) of pure ZnO nanoparticles, which were prepared by coprecipitation method. Magnetization measurement indicates that the ZnO nanoparticles annealed in air at 450, 550, 650, and 800 °C exhibit the RTF and the decrease in the ferromagnetism is performed with the increase in annealed temperature. Selected area electron diffraction, x-ray diffraction, and x-ray photoelectron spectroscopy measurements show that all the samples possess a typical wurtzite structure and no other impurity phases are observed. The results of the Raman spectra indicate that there are lots of defects existing in the fabricated samples. It is also found that the ferromagnetism of ZnO nanoparticles increases after annealing in vacuum condition and decreases after annealing in a rich-oxygen atmosphere. These results confirm that the oxygen vacancies play an important role in introducing ferromagnetism for the ZnO nanoparticles in our case.

In situ fabrication of Co90Nb10 soft magnetic thin films with adjustable resonance frequency from 1.3to4.9GHz

In this work, we realized in situ fabricated Co90Nb10 soft magnetic thin films, with variable in-plane uniaxial magnetic anisotropy, without using the field induced method or postfabrication treatment. In situ control over the in-plane uniaxial magnetic anisotropy field, which varied from 1.6to22.7kAm−1, was achieved by adjusting the deposition oblique angle from 0° to 38°. As a consequence, the resonance frequencies of the films were continuously increased from 1.3to4.9GHz.

Vacancy-Mediated Magnetism in Pure Copper Oxide Nanoparticles

Room temperature ferromagnetism (RTF) is observed in pure copper oxide (CuO) nanoparticles which were prepared by precipitation method with the post-annealing in air without any ferromagnetic dopant. X-ray photoelectron spectroscopy (XPS) result indicates that the mixture valence states of Cu1+ and Cu2+ ions exist at the surface of the particles. Vacuum annealing enhances the ferromagnetism (FM) of CuO nanoparticles, while oxygen atmosphere annealing reduces it. The origin of FM is suggested to the oxygen vacancies at the surface/or interface of the particles. Such a ferromagnet without the presence of any transition metal could be a very good option for a class of spintronics.

Ferromagnetism in freestanding MoS2 nanosheets

Freestanding MoS2 nanosheets with different sizes were prepared through a simple exfoliated method by tuning the ultrasonic time in the organic solvent. Magnetic measurement results reveal the clear room-temperature ferromagnetism for all the MoS2 nanosheets, in contrast to the pristine MoS2 in its bulk form which shows diamagnetism only. Furthermore, results indicate that the saturation magnetizations of the nanosheets increase as the size decreases. Combining the X-ray photoelectron spectroscopy, transmission electron microscopy, and electron spin resonance results, it is suggested that the observed magnetization is related to the presence of edge spins on the edges of the nanosheets. These MoS2 nanosheets may find applications in nanodevices and spintronics by controlling the edge structures.

Adjust the resonance frequency of (Co90Nb10/Ta)(n) multilayers from 1.4 to 6.5 GHz by controlling the thickness of Ta interlayers

In this work, the static and high frequency magnetic properties of (Co90Nb10/Ta)(n) multilayers have been investigated. The results show that the in-plane uniaxial magnetic anisotropy fields can be adjusted from 12 to 520 Oe only by decreasing the thickness of Ta interlayers from 8.0 to 1.8 nm. As a consequence, the resonance frequencies of the multilayers continuously increased from 1.4 to 6.5 GHz. It was found that the changes in the in-plane uniaxial anisotropy field are ascribed to the interlayer interactions among the magnetic layers by investigating the delta M(H) curves.

Manifestation of unexpected semiconducting properties in few-layer orthorhombic arsenene

In this letter, we demonstrate that few-layer orthorhombic arsenene is an ideal semiconductor. Owing to the layer stacking, multilayer arsenenes always behave as intrinsic direct bandgap semiconductors with gap values of approximately 1 eV. In addition, these bandgaps can be further tuned in its nanoribbons. Based on the so-called acoustic phonon limited approach, the carrier mobilities are predicted to approach as high as several thousand square centimeters per volt–second and to simultaneously exhibit high directional anisotropy. All these characteristics make few-layer arsenene promising for device applications in the semiconducting industry.

Ferromagnetism in ultrathin VS2 nanosheets

Two-dimensional nanosheet crystals have potential applications in nano-electronic devices. Prompted by the recently observed ferromagnetism in pristine VX2 (X = S and Se) monolayers by first-principle calculations, we provide the experimental evidence for room temperature ferromagnetism in ultrathin VS2 nanosheets by observing their clear hysteresis and ferromagnetic resonance. The first-principle calculation results indicate that unusual hybridization of the V 3d and S 3p orbitals occurs in the monolayer VS2, and the relative transfer of electrons between the V and S atoms plays an important role in the transition of the spin moments. According to the previous work, the stable ferromagnetism in ultrathin VS2 nanosheets is considered as a competitive effect between through-bond and through-space interactions, where the through-bond interactions dominate. This finding opens a new path to explore the spintronics in pristine two-dimensional nanostructures.

Synthesis, Magnetic Anisotropy and Optical Properties of Preferred Oriented Zinc Ferrite Nanowire Arrays

Preferred oriented ZnFe2O4 nanowire arrays with an average diameter of 16 nm were fabricated by post-annealing of ZnFe2 nanowires within anodic aluminum oxide templates in atmosphere. Selected area electron diffraction and X-ray diffraction exhibit that the nanowires are in cubic spinel-type structure with a [110] preferred crystallite orientation. Magnetic measurement indicates that the as-prepared ZnFe2O4 nanowire arrays reveal uniaxial magnetic anisotropy, and the easy magnetization direction is parallel to the axis of nanowire. The optical properties show the ZnFe2O4 nanowire arrays give out 370–520 nm blue-violet light, and their UV absorption edge is around 700 nm. The estimated values of direct and indirect band gaps for the nanowires are 2.23 and 1.73 eV, respectively.

BaFe12O19 Single-Particle-Chain Nanofibers: Preparation, Characterization, Formation Principle, and Magnetization Reversal Mechanism

BaFe(12)O(19) single-particle-chain nanofibers have been successfully prepared by an electrospinning method and calcination process, and their morphology, chemistry, and crystal structure have been characterized at the nanoscale. It is found that individual BaFe(12)O(19) nanofibers consist of single nanoparticles which are found to stack along the nanofiber axis. The chemical analysis shows that the atomic ratio of Ba/Fe is 1:12, suggesting a BaFe(12)O(19) composition. The crystal structure of the BaFe(12)O(19) single-particle-chain nanofibers is proved to be M-type hexagonal. The single crystallites on each BaFe(12)O(19) single-particle-chain nanofibers have random orientations. A formation mechanism is proposed based on thermogravimetry/differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and transmission electron microscopy (TEM) at six temperatures, 250, 400, 500, 600, 650, and 800 °C. The magnetic measurement of the BaFe(12)O(19) single-particle-chain nanofibers reveals that the coercivity reaches a maximum of 5943 Oe and the saturated magnetization is 71.5 emu/g at room temperature. Theoretical analysis at the micromagnetism level is adapted to describe the magnetic behavior of the BaFe(12)O(19) single-particle-chain nanofibers.

d0 ferromagnetism in undoped sphalerite ZnS nanoparticles

We report the sulfur vacancies-related d0 ferromagnetism in undoped sphalerite ZnS nanoparticles. Systematically tune of sulfur deficiency in ZnS nanoparticles was done by selecting different synthesized temperatures and varying the ratio of hydrogen and argon in post-annealing processes. Our study suggests that such sulfur vacancies can induce the room temperature ferromagnetism. Importantly, the ferromagnetism can be modulated by changing the concentration of sulfur vacancies in the samples. This finding should be the focus of future electronic and spintronic devices.