Search

FeCo films with various thicknesses were fabricated by direct-current magnetron sputtering on corning glass and organic ferroelectric PVDF substrates at the same time with 5 nm Ru seed layer and 5 nm Ta protective layer. The in-plane uniaxial anisotropy field of FeCo on glass substrate increases from 24 to 36 Oe with the increase of FeCo film thickness from 5 to 100 nm. However, a large in-plane anisotropy field of FeCo on PVDF substrate increases with FeCo thickness from 5 to 20 nm and gradually decreases with the FeCo thickness further increasing. Atomic force microscope images of FeCo on glass show quite smooth surface with root-mean-square roughness around 0.5 nm and have none visible granules on the surface for all samples. While, AFM images of FeCo on PVDF show quite rough surface with RMS roughness around 25 nm and have visible granules with the smallest granules appearing at the FeCo thickness of 20 nm. The permeability spectra show the typical ferromagnetic resonance phenomenon and can be well fitted by the LLG equation with the obtained experimental parameters. The ferromagnetic resonance frequency can reach 7.0 GHz for the 20 nm FeCo film on PVDF. Moreover, the quality factor of this sample can respectively reach 26, 12 and 7 at 1.0, 2.0, and 3.0 GHz, indicating the potential real 3G application for high-frequency devices.

The interface has become an important issue in organic magnetic spin-valves. In this work, Si/FeCo/Ta, Si/FeCo/Bepp2/Ta, and Si/Bepp2/FeCo/Ta samples with the variation of the FeCo layer thickness were fabricated by direct-current magnetron sputtering for FeCo layers and the thermal evaporation method for Bepp2 layers. The interaction at the interfaces between the FeCo magnetic layer and Bepp2 organic layer was investigated by the traditional magnetic properties measurement and X-ray photoelectron spectroscopy with the Argon ion etching technique. The experimental results show that the interfacial reaction is strong when sputtering FeCo on Bepp2 layer due to the high energy of sputtered FeCo atoms in contrast with the weak interfacial reaction when evaporating Bepp2 on FeCo layer. Moreover, the capping layer of Ta is quite important to protect FeCo layer against oxidation from air either by direct contact or through Bepp2 layer. Our experiment is very helpful for fabricating organic spin-valves with high-spin injection efficiency.

The field emission (FE) properties of vertically aligned carbon nanotube (CNT) arrays having a surface decorated with Ta layer were investigated. The CNTs with 6 nm thickness of Ta decoration showed improved FE properties with a low turn-on field of 0.64 V/mu m at 10 mu A/cm(2), a threshold field of 1.06 V/mu m at 1 mA/cm(2) and a maximum current density of 7.61 mA/cm(2) at 1.6 V/mu m. After Ta decoration, the increased emission centres and/or defect sites on the surface of CNTs improved the field enhancement factor. The work function of CNTs with Ta decoration measured with ultraviolet photoelectron spectroscopy decreased from 4.74 to 4.15 eV with increasing Ta thickness of 0-6 nm. The decreased work function and increased field enhancement factor were responsible for the improved FE properties of the vertically aligned CNTs. Moreover, a significant hysteresis in the cycle-testing of the current density with rising and falling electric field process was observed and attributed to the adsorption/desorption effect, as confirmed by the photoelectron spectrum. (C) 2014 Elsevier Ltd. All rights reserved.

The field emission behavior of aligned carbon nanotubes (CNTs) is remarkably improved by decorating their surfaces with Ti nanoparticles through a sputtering process. The CNT/Ti(4 nm) sample shows a low turn-on field of 0.63 V/lm at 10 mu A/cm(2), low threshold field of 1.06 V/mu m at 1 mA/cm(2), and maximum field emission current density of 23 mA/cm(2) at 1.80 V/mu m. The enhanced field emission properties of the CNT/Ti samples are attributed to the added defect sites and Ti nanoparticles, which increase the field enhancement factor and density of emission sites. Stability measurements indicate that the Ti coating, which acts as a protective layer, also strengthens the field emission stability of the CNT arrays. Moreover, the extent of hysteresis in the current-voltage sweep highly depends on the voltage-sweep speed. (C) 2013 Elsevier B.V. All rights reserved.

The magnetic spectra of two magnetostatic coupled ferromagnetic stripes with different distances were investigated by the three-dimensional object oriented micromagnetic framework (OOMMF) code. The studied systems exhibit two resonance peaks. The higher peak can be identified with the bulk mode predicted by the macroscopic LL model. The lower peak originates from edge magnetic moments. Influence of magnetostatic interaction on the two resonance models was studied in detail. As the distance between two stripes increases, the magnetic spectrum of two stripes is close to the case of a single stripe.

Co nanowire arrays with three typical diameters of 20, 50 and 120 nm have been fabricated into anodic alumina oxide templates using an ac electrodeposition method. It is found that the crystal texture of the Co nanowires depends on the pH value of the deposition electrolyte. X-ray diffraction results show that the (1 0 0) texture appears at pH 6.2, while the diffraction peaks of (1 0 0) and (1 0 1) appear at pH 6.4 with the diameter of 20 nm. In addition, the (0 0 2), (1 0 0) and (1 0 1) peaks appear with an increase of pH value for the nanowire arrays with diameters of 50 and 120 nm, respectively. Magnetic measurements indicate the effect of structure on the magnetic properties of the nanowire arrays, which depend strongly on the different diffraction peaks, as adjusted by the pH value.