Guanghui Chen

Two new all‐organic complexes with electrical bistable states

Two all‐organic complexes, MC+TCNQ and BBDN+TCNQ, with electrical bistable states at room temperature have been discovered. The resistivity of these thin films prepared in vacuum can be transferred from high to low under a voltage of few volts. The transition time is <100 ns. Therefore, both materials are suitable for making write‐once read‐only memories.

Temperature-dependent magnetic anisotropies in epitaxial Fe/CoO/MgO(001) system studied by the planar Hall effect

Exchange-induced in-plane magnetic anisotropies in a single-crystalline Fe/CoO/MgO(001) system were quantitatively investigated using the planar Hall effect as a function of temperature. Field cooling can induce a strong uniaxial anisotropy in Fe film with the easy axis along the CoO〈110〉 directions close to the cooling field direction. The exchange coupling also induces a 4-fold anisotropy with the easy axis along the CoO〈100〉 directions. Our results prove that the strong magneto-crystalline anisotropy of CoO antiferromagnetic spin plays a significant role in exchange-induced anisotropy.

Four-fold magnetic anisotropy induced by the antiferromagnetic order in FeMn/Co/Cu(001) system

Single crystalline FeMn/Co bilayers were grown epitaxially on Cu(001) and investigated by magneto-optic Kerr effect (MOKE). By doing the MOKE measurement within a rotating magnetic field, we were able to retrieve quantitatively the anisotropy constant of the ferromagnetic Co layer. We show unambiguously that as the FeMn layer changes from paramagnetic (PM) to antiferromagnetic (AFM) states, it enhances the interfacial magnetic anisotropy at the FeMn/Co interface by an order of magnitude. A thickness dependent study of the magnetic anisotropy constant revealed that this induced magnetic anisotropy may originate from the FeMn/Co interfacial spin frustration.

Revealing the volume magnetic anisotropy of Fe films epitaxied on GaAs(001) surface

The in-plane magnetic anisotropy in Fe films grown on GaAs(001) was investigated quantitatively by the magneto-optic Kerr effect with a rotating magnetic field. The clear 1/dFe relation of the uniaxial magnetic anisotropy indicates a surprising volume contribution with easy axis along the GaAs [11¯0] direction. Such volume anisotropy was found to be sensitive to the growth temperature and also strongly correlate with the interface anisotropy. Our results may introduce a new aspect for further understanding the origin of uniaxial magnetic anisotropy in Fe/GaAs(001) system.

UV–visible absorption changes of lead silicate glasses after UV laser irradiation

Abstract UV–visible absorption spectra of binary lead silicate glasses with different lead concentrations were measured after irradiation with the frequency-quadrupled output of a Q-switched YAG laser (266 nm, 10 Hz repetition rate). Two different changes of absorption spectra after exposure to laser beams with different energy densities were observed. This implied that the formation of defects in lead silicate glasses was connected to the UV beam energy density.

In-plane magnetic anisotropy in Fe/MgO/GaAs(001) system

The in-plane magnetic anisotropy in the Fe/MgO/GaAs(001) system has been carefully studied as a function of MgO thickness. The epitaxial relation is Fe(001)[110]//MgO(001)[100]//GaAs(001) [100] for dMgO >1 monolayer (ML). The interfacial uniaxial anisotropy was greatly reduced by the MgO interlayer, and the easy axis of the fourfold anisotropy was found to rotate from the GaAs〈100〉 direction to the GaAs〈110〉 direction. Such anisotropy transition happens within the 1.2 ML MgO thickness range.

Optical Properties and Laser Output of Heavily Yb-Doped Fiber Prepared by Sol-Gel Method and DC-RTA Technique

Heavily Yb-doped (14300 ppm) preforms and fibers were prepared by the sol-gel method and dip coating-rapid thermal annealing technique. Optical properties of these preforms and fibers were measured and discussed. A fiber laser at a 1053-nm wavelength was realized and its slope efficiency was measured to be 88.4%. The excellent performance of the fiber laser and repeatability show that the novel approach described in this paper is capable of providing low-cost high-level rare earth-doped fibers for amplifiers and fiber lasers.

Quantum Well States and Oscillatory Magnetic Anisotropy in Ultrathin Fe Films

The magnetic anisotropy of Fe film grown on vicinal Ag(1,1,10) surfaces studied with the in situ magneto-optic Kerr effect shows oscillatory behavior. We found that both the in-plane step-induced uniaxial anisotropy and the perpendicular anisotropy measured at low temperature show strong oscillations as a function of Fe thickness with a period of ~ 5.7 monolayers. Such novel oscillation of the anisotropy is attributed to the quantum well states (QWS) of d-band electrons at the Fermi level in the Fe film. These QWS have been observed by angle-resolved photoemission spectroscopy from a Fe wedge films grown on Ag(001) surface.

Magnetic anisotropy in Fe films epitaxied by thermal deposition and pulse laser deposition on GaAs(001)

The in-plane magnetic anisotropy of Fe films fabricated with thermal deposition (TD) and pulse laser deposition (PLD) techniques on GaAs(001) substrate was studied quantitatively. The volume anisotropy in TD Fe film is attributed to the constant strain anisotropy, supported by reflection high-energy electron diffraction analysis. The PLD growth was found to deeply influence the interface anisotropy at Fe/GaAs interface even through a 30 ML Fe TD underlayer. The volume anisotropy was found to exist in TD Fe film even grown on top of a PLD film. Our study indicates that the uniaxial magnetic anisotropy in Fe/GaAs(001) system can be controlled by a combination of TD and PLD growth.

The photosensitivity and ultraviolet absorption change of Sn-doped silica film fabricated by modified chemical vapor deposition

10.5μm thick Sn-doped silica films were prepared by the modified chemical vapor deposition followed by the solution-doping method. The films were exposed to 248 and 266nm laser light, respectively. Positive refractive index change up to 2×10−4 at 1550nm was observed by measuring the reflectivity based on Fresnel formulas. The data of UV absorption spectra suggest that the photosensitivity of the Sn-doped silica film under high energy density laser irradiation should be mainly due to the bond breaking of oxygen deficient defects, while under relatively low energy density laser irradiation, the refractive index change probably originates from photoconversion of optically active defects.