H. Z. Chen

Effect of the substitutions of Ni3+, Co3+, and Fe3+ for Mn3+ on the ferromagnetic states of the La0.7Pb0.3MnO3 manganite

The substitution at the Mn site of various transitional metal elements dramatically modifies the magnetic and electronic properties of the La0.7Pb0.3Mn0.8Me0.2O3 (Me=Ni, Co, and Fe) manganites. The powder x-ray diffraction pattern shows a single-phase rhombohedral distorted perovskite structure with space group R3c (No. 167) for all samples. The present article is focused on the effects induced by the partial substitution of Ni, Co, and Fe for the Mn site. The field cooled–zero field cooled curves indicate that the magnetic order is modified from a ferromagnetic long-range spin order for La0.7Pb0.3MnO3 to a spin cluster induced short-range spin order for all the doped compositions. The saturation magnetization, transition temperature, and resistance peak temperature decrease significantly from Ni-doped, Co-doped, to Fe-doped composition. In conclusion, the variation of the magnetic and electronic behaviors is due to the dissimilar 3d electron configuration of the substitutions.

Evolution of Magnetotransport Properties and Spin-Glass Behavior of the La0.7-xNdxPb0.3MnO3 System

The effect of neodymium substitution on the lanthanum site in La0.7-xNdxPb0.3MnO3 perovskite polycrystalline has been systematically studied. The substitution of neodymium for lanthanum causes structure change from rhombohedral to orthorhombic. Ferromagnetism is suppressed as neodymium content increases. The magnetic order changes from a ferromagnetic long-range order with x=0.0 to a spin-glass nature with x=0.7. Besides, the ferromagnetic-paramagnetic transition temperature values are lower for the neodymium phases than for the lanthanum ones. Therefore, the introduction of neodymium degrades symmetry of the structure, diminishes the spin-coupling exchange interaction, and results in changes of magnetic properties. This fact is in good agreement with increasing the B value in Blochs T3/2 law and decreasing the spin-wave stiffness parameter D in quadratic dispersion relation.

Structure characterization and magnetic properties of Ln0.7Pb0.3MnO3 (Ln=La, Nd, and Pr) manganites

Abstract Ln 0.7Pb0.3MnO3 (Ln=La, Nd, Pr) oxides have been synthesized by using the conventional ceramic method. The magnetic measurements show that Tc values alter considerably by substituting different rare earth ions. The zero field cooled (ZFC) magnetization curve of La manganite shows almost the same magnitude with the field cooled (FC); however, the curve of Nd manganite drops to zero at low temperatures. The magnetization is hardly saturated by the external field for Pr and Nd manganites due to the spin-glass nature. These facts are in good agreement with the lower ionic radii of the Nd ions and the corresponding large distortion of their perovskite structures.

Structural and magnetic properties in La0.7Pb0.3Mn1-XCoxO3 systems

Abstract In this study we present the results of an extensive structural investigation of the La 0.7 Pb 0.3 Mn 1− X Co X O 3 (0≦ x ≦1) system. Powder X-ray diffraction shows a single-phase rhombohedral distorted perovskite structure for all samples. There is a gradual decrease in the lattice parameter as the Co content increases. In addition, we have systematically investigated the magnetic properties by using a SQUID magnetometer. The magnetoresistances are also measured and a giant negative magnetoresistance of over 50% can be obtained.

Magnetization processes in polycrystalline (La0.7-xNdx)Pb0.3MnO3

Abstract Magnetization processes for the Nd substitution on the La site in polycrystalline (La 0.7− x Nd x )Pb 0.3 MnO 3 have been systematically studied. The low-field magnetic behavior observed in ZFC and FC curves shows a long-range spin order for La-rich compounds and a spin-glass state for Nd-rich ones. Magnetic hysteresis loops with high field show square curves for all samples. The hysteresis behavior can be modeled by the formula of M = M s (1– a / H n ) where 0≦ n ≦1. The term a / H n expresses the deviation of magnetization from saturation. The larger factor n and smaller factor a for La-rich samples resulting in sharper square curves which should be associated with the long-range spin order of magnetic moment.

Thickness effect of sputtered ZnO seed layer on the electrical properties of Li-doped ZnO nanorods and application on the UV photodetector

Well-defined Zn0.9Li0.1O nanorods were hydrothermally synthesized at the low temperature of 90°C on the sputtered ZnO seed layer in different thickness, 20 nm and 50 nm. The x-ray diffraction patterns of both samples with a single diffraction peak (002) showed the same wurtzite hexagonal structure. The length and diameter of the nanorods were both increased from 1.12 μm to 1.47 μm and 95 nm to 113 nm, respectively, while increasing the sputtered ZnO seed layer thickness from 20 nm to 50 nm. The optical properties were influenced by the presence of oxygen vacancies induced by Li doping in the Zn0.9Li0.1O nanorods. Besides, p-type ZnO-based semiconductor nanorods were obtained by the doping of Li into ZnO. Finally, the UV photodetectors with (p-Zn0.9Li0.1O nanorods)/(n-Si substrate) structure were also achieved. The I-V characteristics of the UV photodetector with p-ZnO:Li nanorod/n-Si structure were also measured. The UV illumination/dark current ratio of the photodetectors with different seeded layer, 20nm and 50nm, were also measured as 201% and 364%, respectively.

INFLUENCE OF GRAIN SIZE OF ZnO NANOCRYSTALLINE FILMS FOR APPLICATION IN DYE-SENSITIZED SOLAR CELLS

The preferred (002) orientation Zinc oxide (ZnO) nanocrystalline thin films have been deposited on ITO-coated glass substrates by means of sol-gel spin-coating technology and rapid thermal annealing for use in dye-sensitized solar cells (DSSC). The effects of annealing temperature (400 ~ 700 °C) on the microstructure and morphology of ZnO thin films were studied. With the increase of heating temperature from 400 °C to 700 °C, the grain size of ZnO thin films decreases from 80 to 10 nm. The decreases in grain size of ZnO thin films contributed to the improvement on the absorption of dye onto the films. The ITO/ZnO/RuL2(NCS)2 electrodes with high absorption in the wide range containing visible light reveal that the nanoporous structure can adsorb easily the dye and can be expected in the application of DSSC.

COMPARISON OF THE MAGNETIZATION BEHAVIORS IN PEROVSKITE COMPOUNDS La0.7-xLnxPb0.3MnO3 (Ln=Pr AND Sm)

The magnetization behaviors of two manganite oxide systems, La0.7-xLnxPb0.3MnO3 (Ln=PrandSm), have been synthesized. The replacement of La ions by Pr or Sm results in a considerable decrease in the ferromagnetic ordering temperature TC and clearly irreversible behavior in the zero-field-cooling-field-cooling curve at a low applied field, showing a short-range spin order phase. These facts are in agreement with the smaller ionic radii of Pr (0.130 nm) and Sm (0.124 nm) ions in contrast to La ion (0.136 nm), and the corresponding larger distortion of perovskite structures. The saturation magnetization MS decreases as Sm content increases relative to the increase of MS as Pr content increases. This can be interpreted in terms of the competition between suppression of ferromagnetism due to structure tuning induced by the small ionic radius of the interpolated cations into the La-site and the increase of ferromagnetically interacting spins due to the introduction of magnetic Pr or Sm ions with f-shell electrons.

Synthesis and magnetic characterization of the La0.6Ln0.1Pb0.3MnO3(Ln=Pr, Nd, and Y) manganites

La0.6Ln0.1Pb0.3MnO3(Ln=Pr, Nd, and Y) oxides have been synthesized by a standard ceramic fabrication method. The partial replacement of La ions by small amounts of Pr, Nd, or Y ions results in a considerable decrease in the ferromagnetic transition temperature and clearly irreversible behavior in the field-cooling–zero-field-cooling curve at low field, showing a short-range spin order phase. These facts are in agreement with the smaller ionic radii of Pr, Nd, and Y ions in contrast to La ions, and the corresponding larger distortion of perovskite structures. The hysteresis loops of these samples illustrate that the magnetization still remains unsaturated in high field and the saturation moments are larger for Pr-doped and Nd-doped manganites. This can be interpreted in terms of canted spins between Mn ions and magnetic Pr or Nd ions with f-shell electrons.

Synthesis and Magnetic Properties of Ferrite Films Prepared Using the Co-Precipitation Technique

Nanoparticle films of ferrite were synthesized using the chemical co-precipitation technique. It was shown that densely packed ferrite films with a thickness of 7 μ m can be deposited from fine particles with an average particle size of 10–20 nm on the Si substrate. The particle size, composition, and magnetic properties of the films are affected by the pH value of the reactive solutions. For samples with a lower pH value, the particles are small and agglomerate together. Conversely, for samples with a higher pH value, the particles are large and uniformly distributed. Samples fabricated with a higher pH value show large values of magnetization and lower values of coercive force. The result of larger magnetization relates to larger particle size and a more uniform distribution for samples fabricated with a higher pH value.