The transport properties and magnetoresistance of electron-doped manganate / insulator composites (La 0.8 Te 0.2 MnO 3 ) 1−x /(ZrO 2 )x (x = 0, 0.3, and 0.5) are investigated. It is found that the metal-insulator transition temperature of this system shifts to a lower value as the ZrO 2 content increases. The introduction of ZrO 2 enhances both the domain scattering and electron relative scattering in the metal transport region. In the adiabatic small polaron hopping transport region, the thermal activation energy seems invariable regardless of the ZrO 2 content. The application of a magnetic field promotes the charge transportation capabilities of the composites, and the magnetoresistance is enhanced with an increase of the ZrO 2 content. This could be attributed to the more remarkable modification effect of magnetic field on ordering degree in the composites than in pure La 0.8 Te 0.2 MnO 3 .
Magnetic and electrical properties of polycrystalline La1.3Sr1.7Mn2-xCuxO7 prepared by solid state reaction were investigated. The X-ray diffraction pattern shows that the two samples have Sr3Ti2O7 type perovskite structure. The two samples undergo complex transition with lowering temperature. The x=0 samples, have the two-dimensional short-range ferromagnetic order at T*=231 K and then transform to the three-dimensional long-rangs ferromagnetic state at TC=114 K, at last they enter the canted antiferromagnetic state at TN=56K. The T*, TC and TN are all reduced at the 5% Cu doping level. Additionally, the two samples exhibited two distinct resistivity peaks, which is due to coexistence of the two phases. The metal-insulator transition temperature was decreased but the magnetoresistance was enhanced at the 5% Cu doping level.
Directional solidification of SCN-3wt% H2O was carried out under externally imposed parallel shear flow, and the growth characteristics of dendritic tips, primary arms and secondary arms were investigated. A bright band related to solute boundary layer along the dendritic tip is observed for the first time. It was confirmed that the left-right symmetry of the dendritic tip is broken up by the shear flow, with the dendritic tip tilting toward the upstream side. The tilting angle increases with the pulling rate. Compared with the case of static condition, the primary spacing becomes lager under shear flow, and this is due to the coupling effect of flow and solute fields. The growth of secondary arm is promoted at the upstream side whereas greatly restrained at the downstream side, which is caused by the circumfluence among dendrites produced by force flow.
In this paper, we perform the quantitative phase-field simulations based on the surface morphology and growth regime of the hexagonal GaN spiral structure. We investigate the highly anisotropic energy, the deposition rate and the kinetic attachment and detachment effects. A regularized equation including the modified gradient coefficient is employed to study the anisotropic effect. Results show that the highly anisotropic energy modulates the equilibrium state by changing the local curvature of the tip step and thus leading to the changed spiral spacing. Under the weak anisotropy, the spiral spacing and morphology keep stable with the increase of the anisotropic strength. In the case of facet anisotropy, however, the larger anisotropic strength facilitates the spiral growth due to the local interfacial instability caused by increasing the supersaturation for the tip step. As to the effect of deposition, the deposition rate imposes the reaction on the curvature of interface due to the variations of supersaturation and step velocity. The larger rate of deposition enables the shorter spacing for both anisotropic and isotropic spirals. We carry out a convergence study of spiral spacing with respect to the step width to estimate the precision of the phase-field simulation. Results show that the larger deposition rate and the higher anisotropy give rise to the lower convergence of the spiral model. Moreover, we find that the kinetic attachment affects the instinct regime of spiral growth by changing the step spacing and the scaling exponents of spiral spacing versus deposition rate. The anisotropic spiral exhibits the more significant hexagonal structure and the lower value of step velocity by reducing the value of kinetic coefficient. The scaling exponent decreases with anisotropy increasing, but it increases with kinetic effect strengthening. The highly anisotropic energy contributes to weakening the sensitivity of the spiral spacing to the kinetic effect.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.