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.
The unexpected room temperature ferromagnetism in pure sodium chloride (NaCl) particles with different crystal size synthesized by breaking at different times is attributed to surface defects, which provides a novel opportunity to further understand the origin of ferromagnetism in the traditional "nonmagnetic" inorganic non-metallic materials. The results of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy suggest that breaking progress does not change the samples' body, but drastically reduces the size of the samples, what's more, it is found to enhance the strength of the ferromagnetic component with decreasing the samples' size through magnetism measure; the first-principle calculation results confirm the experimental conclusion. Ferromagnetism originates from surface effect, probably the long range ferromagnetic interactions between the surface Cl vacancies.
The crystal structure of the high Tc superconducting phase in a Pb-doped Bi-Sr-Ca-Cu-O system (nominal composition Pb0.3Bi1.7Sr2Ca3Cu4OY) with a zero-resistance temperature of 107 K was determined with transmission electron microscopy. The investigation shows that the crystal structure, which is different from the Pb-free one, is monocline with dimensions a=0.532 nm, b=0.383 nm, c=3.71 nm, α=β=90° and γ=134.8°. A distinct change of wave vector of incommensurate modulation was also observed.
Nanoparticles of superconducting YBa2Cu3O7−δ were synthesized via a citrate pyrolysis technique. Room temperature ferromagnetism was revealed in the samples by a vibrating sample magnetometer. Electron spin resonance spectra at selected temperatures indicated that there is a transition from the normal to the superconducting state at temperatures below 100 K. The M–T curves with various applied magnetic fields showed that the superconducting transition temperatures are 92 K and 55 K for the air-annealed and the post-annealed samples, respectively. Compared to the air-annealed sample, the saturation magnetization of the sample by reheating the air-annealed one in argon atmosphere is enhanced but its superconductivity is weakened, which implies that the ferromagnetism maybe originates from the surface oxygen defects. By superconducting quantum interference device measurements, we further confirmed the ferromagnetic behavior at high temperatures and interesting upturns in field cooling magnetization curves within the superconducting region are found. We attributed the upturn phenomena to the coexistence of ferromagnetism and superconductivity at low temperatures. Room temperature ferromagnetism of superconducting YBa2Cu3O7−δ nanoparticles has been observed in some previous related studies, but the issue of the coexistence of ferromagnetism and superconductivity within the superconducting region is still unclear. In the present work, it will be addressed in detail. The cooperation phenomena found in the spin-singlet superconductors will help us to understand the nature of superconductivity and ferromagnetism in more depth.
Zr doped ZnO nanoparticles are prepared by the sol-gel method with post-annealing. X-ray diffraction results show that all samples are the typical hexagonal wurtzite structure without any other new phase, as well as the Zr atoms have successfully entered into the ZnO lattices instead of forming other lattices. Magnetic measurements indicate that all the doping samples show room temperature ferromagnetism and the pure ZnO is paramagneism. The results of Raman and X-ray photoelectron spectroscopy indicate that there are a lot of oxygen vacancies in the samples by doping element of Zr. It is considered that the observed ferromagnetism is related to the doping induced oxygen vacancies.
Abstract Magnetoelectric composites (x)PbZr 0.52 Ti 0.48 O 3 (PZT)-(1-x)NiFe 2 O 4 (NFO) with x values of 0.15, 0.30, 0.45, 0.55, 0.75, and 0.85 mol% were obtained by traditional solid phase reaction. The measured magnetic and magnetostriction properties are strongly dependent upon the molar fraction (1-x) of the NFO in the composites. The maximum magnetostriction coefficient of -52.4 ppm was observed in 0.3PZT-0.7NFO composite ceramic. All the magnetostriction in the composites is larger than the reported values. The larger magnetostriction would result from the magnetoelectric (ME) effect of the composites. We propose a model of the magnetostriction within the composites consisting of strain and polarization. The relationship between the ME effect and magnetostriction is discussed in the qualitative features of this model. This magnetoelectric composite material maintains a strong magnetostrictive effect, which can be used in multifunctional sensors. It will provide new ideas for the design of multifunctional sensors in the future.
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