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/μm at 10 μA/cm2, a threshold field of 1.06 V/μm at 1 mA/cm2 and a maximum current density of 7.61 mA/cm2 at 1.6 V/μm. 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.

Strip-like FeCo films were patterned by a traditional lithograph process from intrinsically isotropic continuous FeCo films. The strip-patterned FeCo film shows a strong in-plane uniaxial magnetic anisotropy with easy axis along the length direction of the strip. The angular dependences of remanence ratio, switching field, and coercivity indicate that the magnetization reversal mechanism of the strip-patterned FeCo film is coherent rotation and domain wall depinning when the applied field is near the hard axis and easy axis, respectively. The consistency of the experimental hysteresis loops of the strip-patterned FeCo film and calculated hysteresis loops with a simple in-plane uniaxial anisotropy model indicates that the strip-patterned FeCo film behaves as a single domain. The absence of the domain wall and the strong in-plane anisotropy field make the strip-patterned FeCo films have much potential for high-frequency application.

The CrO2 micro rod powder was synthesized by decomposing the CrO3 flakes at a specific temperature to yield precursor and annealing such a precursor in a sealed glass tube. The magneto-transport properties have been measured by a direct current four-probe method using a Cu/CrO2 rods/colloidal silver liquid electrode sandwich device. The largest magnetoresistance (MR) around ~72 % was observed at 77 K with applied current of 0.05 μA. The non-linear I–V curve indicates a tunneling type transport properties and the tunneling barrier height is around 2.2 ± 0.04 eV at 77 K, which is obtained with fitting the non-linear I–V curves using Simmons’ equation. A mixing of Cr oxides on the surface of CrO2 rod observed by X-ray photoemission spectroscopy provides a tunneling barrier rather than a single phase of Cr2O3 insulating barrier. The MR shows strong bias voltage dependence and is ascribed to the two-step tunneling process.

•The surface of the aligned carbon nanotubes is decorated with Ti nanoparticles through a sputtering process.•The enhanced field emission properties of the CNT/Ti samples are mainly attributed to the Ti nanoparticles.•Ti coating also strengthens the field emission stability of the CNT arrays.•The extent of hysteresis in the current–voltage sweep depends on the voltage-sweep speed.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/μm at 10 μA/cm2, low threshold field of 1.06 V/μm at 1 mA/cm2, and maximum field emission current density of 23 mA/cm2 at 1.80 V/μm. 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.Graphical abstract

Co2FeAl nanoparticles were synthesized by reducing the coprecipitated precursor of CoCl2·6H2O, Fe(NO3)3·9H2O and Al2(SO4)3·18H2O under H2 atmosphere with various annealing temperatures and durations. X-ray diffraction and transmission electron microscopy were used to characterize the crystal structure and microstructure of Co2FeAl particles, respectively. The investigation indicates that the crystal structure of Co2FeAl particles tends to be B2 structure, in which atoms are partially ordered. The saturation magnetization and hyperfine field of Co2FeAl particles, which were measured under a vibrating sample magnetometer and a 57Fe Mössbauer spectroscope, are consistent with those of the bulk sample and thin films. Furthermore, the higher annealing temperature and the longer annealing time, the better crystallinity of Co2FeAl and more ordered arrangement of atoms will be. It turned out that the coprecipitation thermal deoxidization method could be an easy and high efficient way to obtain the half-metallic Co2FeAl nanoparticles.

A series of (Fe0.67Co0.33)1 − xSmx (0 ≤ x < 0.25) thin films with thickness around 110 nm have been fabricated on silicon(111) substrates by magnetron co-sputtering at ambient condition with a 2.4 kA/m magnetic field applied in the film plane during deposition. With the Sm concentration increasing, FeCo grain size gradually decreases and FeCoSm film eventually becomes amorphous, while the isotropic magnetic property changes to in-plane uniaxial anisotropy as long as Sm is doped. The investigation of the angular dependence of coercivity and switching field indicates that the magnetization reversal mechanism of FeCoSm film is domain-wall depinning and coherent rotation when the applied field is close to the easy axis and hard axis, respectively. The anisotropy field and the resonance frequency of FeCoSm films can be tuned in the range of 15.0–109.5 kA/m and 5.2–11.8 GHz, respectively, by controlling the content of Sm, indicating that FeCoSm films have much potential in high-frequency applications.Highlights► Magnetic and structural properties of FeCoSm films with variation of Sm are reported. ► The addition of Sm up to a certain level leads to amorphous FeCoSm films. ► In-plane uniaxial anisotropy is obtained as long as Sm is doped. ► Magnetization reversal follows either a Stoner–Wohlfarth model or a Kondorsky model. ► Resonance frequency can be tuned in the range of 5.2–11.8 GHz by the content of Sm.

FeCoNd thin film with thickness of 166 nm has been fabricated on silicon (1 1 1) substrates by magnetron co-sputtering and annealed for one hour under magnetic field at different temperatures (Ta) from 200 °C to 700 °C. The As-deposited and annealed FeCoNd film samples at Ta ≤ 500 °C were amorphous while the ones obtained at Ta ≥ 600 °C were crystallized. We found that the perpendicular anisotropy field gradually decreases as the annealing temperature increases from room temperature to 300 °C. A well induced in-plane uniaxial anisotropy is achieved at the annealing temperature between 400 and 600 °C. The variation of the dynamic magnetic properties of annealed FeCoNd films can be well explained by the Landau–Lifshitz equation with the variation of the anisotropy field re-distribution and the damping constant upon magnetic annealing. The magnetic annealing might be a powerful post treatment method for high frequency application of magnetic thin films.Highlights► FeCoNd thin film with thickness of 166 nm shows the perpendicular anisotropy. ► Perpendicular anisotropy decreases as annealing temperature increases from RT to 573 K. ► In-plane uniaxial anisotropy is achieved as annealing temperature above 400 °C. ► The resonance absorption phenomena around gigahertz were observed for FeCoNd films. ► The as deposited FeCoNd films have much potential for high-frequency application.

A sol–gel method has been used to prepare a series of polycrystalline Ca2−xCexFeMoO6 (x = 0–0.4) double perovskites. Rietveld refinement of X-ray diffraction data indicates that although cell parameters increase slightly, the symmetry of the crystalline structure is preserved upon Ce doping. The partial substitution of Ce3+ for Ca2+ reduces the saturation magnetization, however it considerably enhances the Curie temperature (TC) from 365 K for x = 0 to 393 K for x = 0.4. Transport measurement shows that Ca2−xCexFeMoO6 exhibits metallic behavior, and the resistivity of Ca2−xCexFeMoO6 increases first, and then decreases with the increasing of x. The behavior of the increasing of TC and the decreasing of resistivity upon Ce doping was explained by the electron doping effects.