G.H. Zheng

The effects of surface spin on magnetic properties of weak magnetic ZnLa0.02Fe1.98O4 nanoparticles

In order to prominently investigate the effects of the surface spin on the magnetic properties, the weak magnetic ZnLa0.02Fe1.98O4 nanoparticles were chosen as studying objects which benefit to reduce as possibly the effects of interparticle dipolar interaction and crystalline anisotropy energies. By annealing the undiluted and diluted ZnLa0.02Fe1.98O4 nanoparticles at different temperatures, we observed the rich variations of magnetic ordering states (superparamagnetism, weak ferromagnetism, and paramagnetism). The magnetic properties can be well understood by considering the effects of the surface spin of the magnetic nanoparticles. Our results indicate that in the nano-sized magnets with weak magnetism, the surface spin plays a crucial rule in the magnetic properties.

Separated CoFe2O4/CoFe nanoparticles by the SiOx matrix: revealing the intrinsic origin for the small remanence magnetization

In order to clarify the intrinsic reason for the smaller remanence (Mr)-to-saturation (Ms) magnetization ratio Mr/Ms than that expected by the Stoner–Wohlfarth model in CoFe2O4/CoFe2 nanoparticles in the previous report, we first prepared well-dispersed CoFe2O4 nanoparticles, and then they were diluted in the SiO2 matrix followed by reduction in H2 as far as possible to exclude or reduce disadvantageous variables (such as the growth and aggregation of particles and the exchange coupling between soft magnetic particles in the process of reducing) affecting magnetic properties. Such an idea has not been taken into account before to our knowledge. The analyses on the magnetic results indicate that the CoFe2O4/CoFe2 nanoparticles herein reported are a pure dipolar system, in which the coercivity (Hc) and Mr/Ms ratio are very sensitive to the anisotropy and the strength of dipolar interaction. These results signify that it is important to maintain the CoFe2O4/CoFe2 nanoparticles with higher anisotropy and weaker dipolar interaction for improving Mr/Ms and Hc. This suggestion was further confirmed by our another result wherein an Mr/Ms value of 0.64 was obtained even though no exchange coupling was observed in the CoFe2O4/CoFe2 nanoparticles, and further work is in process.Graphical abstractNumerous efforts have devoted to improve the values of Ms and Mr/Ms by compositing hard CoFe2O4 (CFO) ferrite with soft CoFe2 (CF) alloy, which unfortunately give the low Mr/Ms value (<0.5) even in presence of the exchange coupling. Key issues involve the preparation of CFO/CF composite. Previously the preparation of CFO/CF undergoes the synthesis of CFO and the subsequent reducing in the H2 ambient, as shown in Figure (a), while in this work well dispersed CFO nanoparticles were first prepared , and then diluted in the SiO2 matrix followed by reducing in H2 to exclude or reduce disadvantageous variables, such as the growth and aggregation of particles and the exchange coupling between soft magnetic particles in the process of reducing, as shown in Figure (b). Our results suggest that higher anisotropy and weaker dipolar interaction favor the larger Mr/Ms value, as shown in Figure (c).

Superior visible light photocatalytic performance of reticular BiVO4 synthesized via a modified sol–gel method

Reticular BiVO4 catalysts were successfully synthesized via a modified sol–gel method. Here, citric acid (CA) was used as the chelating agent and ethylenediaminetetraacetic acid (EDTA) was used as the chelating agent and template. Furthermore, the effects of pH values and EDTA on the structure and morphology of the samples were studied. We determined that EDTA and pH played important roles in the determination of the morphology of the as-prepared BiVO4 samples. Photocatalytic evaluation revealed that the reticular BiVO4 exhibited superior photocatalytic performance characteristics for the degradation of methylene blue (MB) under visible-light (λ > 400 nm) exposure, about 98% of the MB was found to degrade within 50 min. Moreover, the degradation kinetics of MB was in good agreement with pseudo-first-order kinetics. The obtained apparent reaction rate constant kapp of reticular BiVO4 was much higher than that of BiVO4 synthesized by the citric acid sol–gel method.

Low thermal conductivity for Sr1−xLaxTiO3

Abstract N type thermoelectric materials Sr1−xLaxTiO3 (x = 0·02, 0·06 and 0·10) have been obtained by hydrothermal method and sintering at 900 and 1100°C. The thermoelectric properties have been measured, and all of the samples in the measured temperature range have been found to be insulating. Very low thermal conductivity κ = 0·75 W m−1 K−1 is found at 500 K for Sr0·9La0·1TiO3 after sintering at 900°C. With increasing doping level x, the thermal conductivity κ decreases. With increasing sintering temperature, the grain size of samples increases, and the thermal conductivity increases. This phenomenon is ascribed to the strong suppression of the electron and phonon conductivities due to scattering by the numerous grain boundary scattering.

Synthesis and photocatalytic properties of Bi2MoO6 nanoparticles prepared via a water-in-oil microemulsion method

ABSTRACT Monodispersed spherical Bi2MoO6 precursors with particle sizes about 20–40 nm were successfully obtained by a water-in-oil microemulsion technique. Well-crystallized Bi2MoO6 photocatalysts were fabricated in control by calcined precursors at different temperatures. The particles were characterized by thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS). The synthesized particles were evaluated as photocatalyst for the degradation of methyl blue (MB) under visible light irradiation. As-prepared Bi2MoO6 photocatalysts exhibited superior photocatalytic activity under visible-light irradiation. The highest MB degrading efficiency of 97.6% in 120 min under visible-light irradiation was observed for the sample calcined at 450°C. Moreover, the degradation kinetics of MB were in good agreement with pseudo-first-order kinetics.

First-principles calculations on spin-polarized transport properties of Mn4O4 cluster

Taking the Mn4O4 cluster as a model system, the spin-polarized transport properties of the small cluster system were systematically probed. The theoretical investigations are based on density-functional theory and non-equilibrium Green’s functional method. The equilibrium transport mechanism is illustrated by the band structure of the electrode, the electronic structure of the Mn4O4 cluster and the coupling between the cluster and the electrodes. To well understand the non-equilibrium mechanisms, one straightforward and simple band-matching model was proposed. Moreover, such a band-matching model can be extended to well illustrate the transport properties of other nano-scale systems.

Effects of Al doping in manganites La0·9Te0·1MnO3

Abstract The effects of Al doping at Mn sites in manganites La0·9Te0·1MnO3 have been studied by preparing the series La0·9Te0·1Mn1−xAlxO3 (0·05≤x≤0·20). All samples can be indexed by rhombohedral lattice with the space group . Upon Al doping, both the Curie temperature TC and magnetisation M are suppressed. The resistivity measurements indicate that there exists a weak metal–insulator transition for the sample with x = 0·05, with an increase in the doping level, the metal–insulator transition disappears and the resistivity increases. Thermopower S(T) exhibits a maximum at TS, which is close to TC, for all samples. By fitting the S(T) and ρ(T) curves, it is found that the temperature dependences of both S(T) and ρ (T) in the high temperature paramagnetic region follow the variable range hopping mechanism for all samples. Thermal conductivity κ(T) values decrease with the increasing Al doping level. The results are discussed according to the destruction of the Mn2+–O–Mn3+ double exchange interaction and the disorder effect due to the Al doping.