S.J. Xie

Diffusion theory of spin injection into organic polymers

Instead of spin electrons or holes, the carriers in polymers are supposed to be spin polarons or spinless bipolarons. Based on the spin diffusion theory and Ohms law, we studied spin-polarized injection into organic polymers. It was obtained that only spin polarons are responsible for the current spin polarization in a ferromagnetic (FM)/organic system. Effects of the conductivity matching and the interfacial resistances on the current spin polarization were discussed.

Spin-polarized current in a ferromagnetic/organic system

Spin-polarized current through a ferromagnetic/organic interface was studied theoretically. This study was stimulated by recent experiments on La1−xSrxMnO3∕Alq3∕Co and La1−xSrxMnO3∕sexithienyl∕La1−xSrxMnO3 structures. According to the spin-diffusion equation, the current spin polarization was obtained by assuming that spin polarons as well as spinless bipolarons to be the carriers in the organic semiconductor. It was found that polarons are the effective spin carriers of a spin-polarized current, even though they constitute only a fraction of all carriers. Effects of interfacial electrochemical-potential difference and conductivity matching on spin polarization of the current are discussed.Spin-polarized current through a ferromagnetic/organic interface was studied theoretically. This study was stimulated by recent experiments on La1−xSrxMnO3∕Alq3∕Co and La1−xSrxMnO3∕sexithienyl∕La1−xSrxMnO3 structures. According to the spin-diffusion equation, the current spin polarization was obtained by assuming that spin polarons as well as spinless bipolarons to be the carriers in the organic semiconductor. It was found that polarons are the effective spin carriers of a spin-polarized current, even though they constitute only a fraction of all carriers. Effects of interfacial electrochemical-potential difference and conductivity matching on spin polarization of the current are discussed.

Investigating the magnetic field effect on electron-hole pair in organic semiconductor devices

By constructing dynamic equations including electrons, holes and their pair densities, we calculate the magnetoconductance (MC) and the magnetoelectroluminescence (MEL) separately. It is indicated that MC and MEL may result from different response on the applied magnetic field. MC is from the scattering of polarons by magnetic field related triplet excitons, while MEL is mainly from magnetic field related conversion between singlet and triplet electron-hole pairs. Furthermore, we discuss the relation between MC and MEL. The theoretical calculations are well consistent with the experimental results.

Stability of CDW and SDW in halogen-bridged mixed-valence transition-metal compounds

Abstract Charge-density-wave (CDW) and spin-density-wave (SDW) are the main ground states of halogen-bridged mixed-valence transition-metal complexes. Their stability was studied in the framework of the tight-binding approximation. It was found that the missing bond-charge repulsion in the extended Hubbard model tends to suppress the CDW. A transition CDW-to-SDW would take place in the case of strong electron–electron (e–e) interactions. In addition, the effect of the dimensions on the CDW and SDW was studied by including the interchain interactions. The calculation showed that interchain interactions intend to suppress the formation of CDW and SDW.

Spin-dependent CPP transport properties of ZnO/ferromagnet heterostructures

Abstract (Co/ZnO/FeNi) 2 multilayer heterostructures were fabricated by a multi-target magnetron sputtering system and photolithography. Their spin-dependent CPP (current perpendicular to plane) transport properties were investigated by magneto-transport measurement. An MR ratio of 3.3% is observed at 77xa0K, which decreased quickly with the increasing of ZnO thickness. No dependence of MR on the magnitude of the measuring current is observed, which indicated the MR is not caused by spin-dependent tunneling.

Dimensional model of carbon nanotubes

A dimensional model was set up to study the electronic and lattice property of single-walled carbon nanotubes. The calculations clearly confirmed the experimental results, which included that armchair-type nanotubes were metallic, zigzag-type semiconductive or metallic depending upon the charity and tube diameters. Our investigation revealed that the quasi-one dimension was the essential characteristic of carbon nanotubes.

NHY coupling model in PtX compounds

Abstract An Nue5f8Hue5f8Y coupling model was supposed on a two-chain system of Ptx (X = Cl, Br, I) to study the role of interchain coupling. It was found that the CDW and BOW are suppressed by the interchain coupling and the CT gap decreases, which is consistent with the pressure experiments of MX compounds.

Optical properties of diblock copolymers

With a tight binding model, the electronic optical properties of diblock copolymers were studied. It was found that the light-emitting wavelength depended on the nature and ratio of the homopolymers. The results were consistent with experiments and quantum chemical calculations, which guided the selection of suitable emitting light (EL) materials.

Effects of magnetic field orientation and injected current density on the output of nano-structured Co/Cu/Fe junctions

Co/Cu/Fe nano-sized sandwich thin films have been prepared by electron beam evapora- tion. 5 μm ×x 5 μm Co/Cu/Fe sandwich heterojunction was made using photolithography and lift-off process. The bipolar output signal of Co/Cu/Fe junctions has been measured and analyzed. The effects of applied magnetic field angle (referring to the normal of the junction plane) and injecting spin-polarized current on the output signals have been studied, and the measured results were discussed.

NHY coupling and localized vibration modes in MX compounds

Abstract The effects of Nue5f8Hue5f8Y coupling on localized vibration modes around the excitations in MX compounds are investigated. It is shown that the localized modes in an isolated chain will be separated into two chains due to an Nue5f8Hue5f8Y coupling. Some new modes of lattice vibration are found, which are achieved by the Nue5f8Hue5f8Y coupling. These results can qualitatively account for the frequency shifts of some modes observed in the Raman and infrared absorption spectra.