Tan Shun

Preparation and electron spin resonance effect of nanometer-sized Mn2O3

Abstract Nanometer-sized manganic oxide (Mn 2 O 3 ) has been prepared for the first time by a chemical liquid homogeneous precipitation (CLHP) method. Transmission electron micrographs and X-ray powder diffraction patterns show that the average particle sizes are in the range of 9–50 nm. From the electron spin resonance (ESR) patterns of 9 nm manganic oxide particle, we can observe hyperfine structure (Six absorption peaks of ESR) of Mn 2+ ion adding the Mn 3+ ion signal.

Fractal formation and tunnelling effects on the conductivity of Au/a-Ge bilayer films

The fractal crystallization of the Au/a-Ge bilayer films has been investigated, and the resistance characteristics have been first measured by the two-probe configuration method. The experimental results suggest that the resistance R of various annealing films are influenced by the fractal formation and the fractal dimension. These phenomena were explained by the Random Tunnelling Junction Network (RTJN) model.

Effect of fractal crystallization on the depositing sequence of a Pd/Ge thin film system

The behavior of fractal crystallization in a Pd/Ge thin film system of various ratios of thickness (or composition) after annealing has been investigated by transmission electron microscope. It is difficult for coevaporated Pd–Ge films to obtain fractal crystallization. The fractal structure in Pd/a-Ge bilayer films can form more easily than in a-Ge/Pd bilayer films. The fractal crystallization was restricted because of the formation of the compounds (Pd2Ge and PdGe) in the Pd/Ge thin film system. Growth of the fractal structure depends on the competition between the two processes of amorphous germanium (a-Ge) crystallization and compound formation. Fractal formation can be explained by a random successive nucleation model.

A high-resolution electron microscopy study of microstructure of ZnS powder phosphors with different dopants

Abstract The microstructures of ZnS phosphors with different dopants and different luminescence mechanisms have been investigated by transmission electron microscopy (TEM). Our observations show that there are evident differences in the microstructures of ZnS: Fe, ZnS: Cu and ZnS: Mn. It is reasonable to infer from the TEM experiments that the photoluminescence probably relates mainly to the various stacking faults and dislocations, whereas the a.c. electroluminescence may have a relationship with the microtwin structure, and the coherent growth state of α- and β-phases may be the reason for the d.c. electroluminescence.

47 K superconductivity in Bi1.6Pb0.4Sr1.65La0.35CuOz

In this paper it is shown that Bi2Sr2CuOz (Bi2201) phase possesses a strong incommensurate modulation structure while Tl2Ba2CuOz (Tl2201) phase does not exhibit this characteristic, which is the origin of the great difference between the superconducting transition temperature of Bi2201 (Tc = 10 K) and that of Tl2201 (Tc = 90 K). Tonsetc = 41 K (Tc0 = 34 K) is first obtained by Pb doping into Bi2201 phase to suppress the modulation structure. The highest Tc of the Bi2201 phase, Tonsetc = 47 K (Tc0 = 39 K), is achieved by Pb and La doping into the Bi2201 phase to suppress the modulation structure and adjust the carrier concentration.

Temperature-induced magnetization reversal in FeCr2−xAlxS4

In this paper, temperature-induced magnetization reversal in FeCr2−xAlxS4 (x = 0.8, 1.0) is reported. Low-field magnetization measurements indicate that this system displays substantial irreversibility between zero-field-cooling (ZFC) and field-cooling (FC) sequences. Upon warming, the ZFC magnetization is found to change sign twice; however, the FC magnetization changes sign only once. Magnetic hysteresis loop measurements reveal that this system displays a large coercivity at lower temperatures; with increasing temperature, the coercivity decreases abruptly. By accounting for magnetic domain freezing induced by large magnetic anisotropy and domain wall pinning of non-magnetic ions, the multiple sign changes of the magnetization are explained qualitatively.

Delocalizing Effect of Polarons in Colossal Magnetoresistance Material FeCr2S4

The electrical transport and magnetic properties of the colossal magnetoresistance material FeCr2S4 are studied. The temperature dependence of resistivity ρ and thermoelectric power S are investigated from 5 to 300 K and from 77 to 300 K, respectively. The activation energy Eρ obtained from ρ-T is larger than the activation energy ES, obtained from S-T. This indicates that magnetic polarons dominate the conduction behaviour at temperatures above Tc. The M-T curve and electron spin resonance spectra show that the paramagnetic-ferromagnetic transition is incomplete, and that a paramagnetic phase coexists with a ferromagnetic phase in a certain temperature range below Tc. It is proposed that the insulator-metal transition near Tc could be attributed to the gradual delocalizing effect from magnetic polarons to naked carriers. The resistivity in the presented temperature range can be described by considering the coexistence of magnetic polarons and naked carriers.

34K superconductivity of Bi2201 system

Abstract In this paper it is analyzed that Bi2201 phase possesses strong incommensurate modulation structure while T12201 phase does not show any modulation characteristic, which is the origin of great difference between superconducting transition temperature of Tl2201 (Tc=90K) and Bi2201 (Tc=10K). Pb doping was performed to weaken the modulation structure of Bi2201 system, and then by adjusting the oxygen concentration to optimal level, the Tc of Bi2201 phase was improved to Tc0=34K(Tconset=41K).

Crystallization and Fractal Formation in Annealed Al/a-Ge Bilayer Films

The crystallization and fractal formation in annealed Al/a-Ge bilayer films were studied. It was found that the effect of metal-mediated crystallization increases with increasing annealing temperature and time. However, fractal patterns could be formed only in samples with proper thickness ratio. Some special phenomena at strain, broken, and step areas are also reported.

Mechanisms of the pancake vortex and vortex line movement in the high T c superconductors Bi 2 Sr 2 CaCu 2 O 8 + δ and La 1.93 Sr 0.07 CuO 4 + δ

In the strict sense, it is not very clear why with magnetic field increasing, the normal-superconductive (NS) transition becomes broad for Bi2Sr2CaCu2O8+δ (Bi2212) while the NS transitions are almost parallel for La1.93Sr0.07CuO4+δ (La214). In this paper, R-T relations are measured by the six-probe method. We propose a moving mechanism of the pancake vortex and vortex line for Bi2212. The theoretical curves fit the experiment data well.