Yu. V. Gulyaev

ELECTRON FIELD EMISSION FROM NANOFILAMENT CARBON FILMS

Abstract Considerable field emission has been observed from the surface of nanofilament carbon structure films on various substrates (Si, quartz, glass): the density of emission current was up to 1 A/cm 2 while the electric field was about 100 V/μm. The ‘reconstruction’ and ‘inversion’ effects of field emission have also been observed on some structures after current breakdown.

Ferromagnetic films with magnon bandgap periodic structures: Magnon crystals

A new type of photonic crystals is proposed. The new crystals have a forbidden gap in the microwave spectrum of magnetostatic spin waves, and, by analogy with photonic crystals, they are called magnon crystals. Specimens of such crystals were fabricated on the basis of yttrium iron garnet films. The surfaces of ferromagnetic films containing two-dimensional etched hole structures were studied by atomic force and magnetic force mag-netometry. The propagation of spin waves through the magnon crystals was investigated.

Field emitter arrays on nanotube carbon structure films

We present the finding of newly performed experiments of considerable field emission from the films consisting of nanotube carbon structures. Density of emission current was up to 1–3 A/cm2, while in 20–100 V/μm electric field it was 0.1–1 mA/mm2.

Thin films consisting of carbon nanotubes as a new material for emission electronics

The investigation results for the emission characteristics of thin films composed of nanotube carbon structures are described. These films are shown to provide high field electron emission and substantial thermal electron emission even at low temperatures. They exhibit low electron work functions and ensure stable field emission under conditions of operating vacuum.

Work function estimate for electrons emitted from nanotube carbon cluster films

Relying on the obtained theoretical and experimental results the electronic work function from a nanotube carbon film was estimated. It was shown that these structures have an electronic work function that is substantially lower than that for graphite. The influence of the film surface relief on its emission was regarded.

Influence of external factors on electron field emission from thin‐film nanofilament carbon structures

The influence of temperature and residual gas pressure on the field emission of thin‐film nanotube carbon structures has been studied. These structures are shown to exhibit low work functions. They are promising for fabrication of effective low‐voltage field emitters and low‐temperature thermal emitters.

Spin-injection terahertz radiation in magnetic junctions

Electromagnetic radiation of 1–10 THz range is observed at room temperature in a structure with a point contact between a ferromagnetic rod and a thin ferromagnetic film under electric current of high enough density. The radiation is due to nonequilibrium spin injection between the components of the structure. By estimates, the injection can lead to inverted population of the spin subbands. The radiation power exceeds by orders of magnitude the thermal background (with the Joule heating taken into account) and follows the current without inertia.

Current-induced inverse population of spin subbands in magnetic junctions

The spin flux matching conditions that should be satisfied at the boundaries between contacting layers of a magnetic junction to ensure the inverse population of spin subbands at experimentally achievable current densities of −107–108 A/cm2 are determined. The essence of the conditions is that an efficient spin injection takes place at the input boundary, whereas the injection at the output boundary is blocked. The fulfillment of the matching conditions for contacting layers with antiparallel magnetization orientations leads to stability in magnetic fluctuations for any forward currents.

Disturbance of spin equilibrium by current through the interface of noncollinear ferromagnets

Boundary conditions are derived that determine the penetration of spin current through an interface of two noncollinear ferromagnets with an arbitrary angle between their magnetization vectors. We start from the well-known transformation properties of an electron spin wave functions under the rotation of a quantization axis. It allows directly find the connection between partial electric current densities for different spin subbands of the ferromagnets. No spin scattering is assumed in the near interface region, so that spin conservation takes place when electron intersects the boundary. The continuity conditions are found for partial chemical potential differences in the situation. Spatial distribution of nonequilibrium electron magnetizations is calculated under the spin current flowing through a contact of two semi-infinite ferromagnets. The distribution describes the spin accumulation effect by current and corresponding shift of the potential drop at the interface. These effects appear strongly dependent on the relation between spin contact resistances at the interface.

Spin-injection mechanism of magnetization reversal and hysteresis of current in magnetic junctions

A novel mechanism is proposed for magnetization reversal by the current of magnetic junctions with two metallic ferromagnetic layers and thin separating nonmagnetic layer. The spin-polarized current flows perpendicularly to the interfaces between the ferromagnetic layers, in one of which the spins are pinned and in the other they are free. No domain structure is formed in the ferromagnetic layers. The current breaks spin equilibrium in the free layer, which manifests itself in the injection or extraction of spins. The nonequilibrium spins interact with the magnetization of the lattice due to the effective field of s-d exchange, which is current dependent. At currents exceeding a certain threshold value, this interaction leads to magnetization reversal. Two threshold currents for magnetization reversal have been obtained theoretically, which are reached as the current increases or decreases, respectively. Thus, the phenomenon of current hysteresis is found. The calculated results are in good agreement with experiments on magnetization reversal by current in three-layer junctions of composition Co(I)/Cu/Co(II) prepared in a pillar form.