Ruzhen Zhang

Low-field MR behaviour in La0.67Ca0.33MnO3/ZrO2 composite system

La0.67Ca0.33MnO3 (LCMO) nanoparticles were prepared by the sol–gel method. The composite samples of (LCMO)x/(ZrO2)1−x were obtained by mixed LCMO and ZrO2 powders and sintered at 1300°C. Detailed studies of magnetic and magnetotransport properties for composite samples have been performed. The x-ray diffraction and scanning electronic microscopy observations indicated that no reaction happened between LCMO and ZrO2 grains. The low-field magnetoresistance (LFMR) can be greatly improved by ZrO2 addition close to the percolation threshold of x = 60%. The field sensitivity of MR at 77 K in the low field region for (LCMO)0.4/(ZrO2)0.6 is 7%/100 Oe, which is one order of magnitude larger than that obtained by pure LCMO. The enhancement of the spin-dependent tunnelling and scattering of electrons at the interfaces of LCMO and ZrO2 grains is responsible for the enhanced LFMR.

Magnetic properties and giant magnetoresistance in Fe0.35(In2O3)0.65 granular film

Fe/In2O3 granular films have been prepared by the radio frequency sputtering method. The magnetic and transport measurements of a representative sample, Fe0.35/(In2O3)0.65, showed that there exist different magnetic states in different temperature regions. At room temperature, the film shows superparamagnetic behaviour, and a 5.2% magnetoresistance (MR) ratio was obtained. The susceptibility measurements showed that the blocking temperature is 50 K. Below a certain freezing temperature Tf of about 10 K, the film transits from the ferromagnetic state to the particle-spin-cluster state. In this event, the MR ratio of the film increases dramatically with decreasing temperature. A maximum giant magnetoresistance (GMR) ratio up to 506% is obtained at the metal–semiconductor transition temperature of about 2.2 K. The mechanism of this GMR is related to the interaction with the impurities influencing the local magnetization which is quite different to the spin-dependent tunnelling effect at room temperature.

Substituting effects of Sm in polycrystalline La-Ca-Mn-O

The Sm substituting effects for La in La0.67Ca0.33MnO3 have been studied systematically. With increasing Sm doping amount, the metal-isolator phase transition temperature for the samples decreases monotonically, the corresponding peak resistivity increases dramatically and the Curie temperature decreases monotonically. The substitution of La-Ca-Mn-O with 0.13% Sm for La improved the magnetoresistance ratio by an order of magnitude. The effects of doping with Sm can be explained in terms of the lattice effects. An irreversible MR behaviour was observed in the Sm-doped compound. This effect was enhanced with increasing Sm doping amount.

Reconstruction of refractive index profiles of 3 MeV O2+ ion-implanted MgO-doped LiNbO3 using wet etching and ellipsometry

A planar waveguide is fabricated by 3 MeV O2+ ion-implanted in MgO-doped lithium niobate, and the refractive index profiles of waveguides are reconstructed based on etching and ellipsometry techniques. The SRIM2003 code is used to simulate the damage distribution induced by implantation. The etching rate versus the etching depth is extracted and the relation between the etching rate and the damage profile is discussed. The index profile of this kind of waveguide is determined by etching in combination with the following ellipsometric measurements. Both ordinary and extraordinary index profiles in waveguide are obtained. The influence of damage profile on index profiles in waveguide, as well as that on waveguide properties is analysed.

MgO:LiNbO3 planar waveguide formed by MeV O2+ implantation and its annealing characteristics

A z-cut magnesium-doped LiNbO3 is implanted by O2+ at 1.5–4.5 MeV and with doses of 4–12 × 1014 ions/cm2 at room temperature. Planar optical waveguides were obtained and characterized by the prismcoupling technique at wavelength of 633 and 1539 nm. Implanted samples were annealed at different temperatures and time durations. After different annealing treatments, mode profiles and optical losses were measured and analyzed.