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The equation of the dynamics of the magnetic moment motion that has been averaged over the ensemble of nonequilibrium spin-injected electrons in a ferromagnetic transition in the presence of exchange interaction, interaction with an external electromagnetic field, and a thermostat has been obtained taking into account the spatial inhomogeneity of the charge carrier distribution. It has been shown that taking into account the spatial inhomogeneity of the charge carrier distribution in the equation of the dynamics of the magnetic moment motion allows for describing the various processes of electron transfer in the magnetic transition. The probability of quantum transitions of electrons with opposite spin directions, which determine spin relaxation in interaction with a thermostat, has been estimated. It has been shown that the anisotropy of the radiation medium is determined not only by the anisotropy of the sd-exchange tensor, but also by the additional anisotropy that is caused by the electron impulse derivatives of this tensor. The considered phenomena have a great potential for the detection of new effects and development of new devices based on them, including compact tunable radiation sources in the terahertz frequency range, which is obviously difficult to generate.

We have studied the effect of substrate temperature and molecular oxygen pressure on the growth of thin (

The dynamics of the motion of the magnetic moment averaged over an ensemble of nonequilibrium spin-injected electrons in a ferromagnetic junction is considered with allowance for the exchange interaction, as well as the interaction with an external electromagnetic field and a thermostat. The solution of this problem is important for the experimental development of compact terahertz-band radiation sources. The rate of quantum transitions of electrons with opposite spins, which determine the spin relaxation under the interaction with a thermostat, is calculated within the density matrix formalism. It is shown that two spin-relaxation modes can be implemented that correspond to low- and high-Q precession of spin-nonequilibrium injected electrons. The effect of the characteristic features of spin-flip transitions under the relaxation of the magnetic moment on the emission and absorption of photons with-energy corresponding to the energy of effective exchange splitting of spin subbands is discussed.

Operating modes of terahertz (THz) generators with “rod–film” magnetic junctions formed by a Fe rod with one pointed end with a diameter of 10–50 nm and various nanometer-thick (single-layer and multilayer) Со films are studied. It is demonstrated that the efficiency of the THz radiation increases (due to an increase in the current density) if the thickness of a single-layer film decreases to the point when it becomes discontinuous (ultrathin) while retains its conductivity. If a multilayer structure with several such films separated by nonmagnetic conductive layers is used, the radiation power can also be increased.

The current–voltage (I–U) characteristics of a cross-shaped metal-dielectric-metal (MDM) Ni/NiO/Fe structures with NiO layers of different thicknesses are investigated. The dependence of the sign of the differential resistance on the current flowing through the structure and on the thickness of the NiO in a four-contact measuring system of potentials is revealed. In a region 8–10 nm thick, the voltage on the structure changes sign thrice and has the form of an N-shaped curve. This dependence is explained by the geometric effect, which appears due to the competition between the vertical and lateral electron transport, when the ratio of the resistances of the dielectric interlayer and metallic leading electrodes changes under the influence of the current. The numerical calculation confirms the experimentally observed I–U dependences.

Half-metallicity, low magnetic damping and high Curie temperatures (TC) are crucial for application in spintronics and full Heusler alloys are promising in this regard. Herein, we have considered Co2FeAl (CFA) and Fe2CoAl (FCA) as representatives of direct and indirect full Heusler compounds which crystallize in L21 and C1b phases, respectively. The theory of L21 type Heusler alloys has been well established; however the fundamental understanding of Fe2CoAl is still under developed. In this paper, we have employed density functional theory (DFT) to study the electronic, elastic and X-ray spectroscopic properties of Co2FeAl and Fe2CoAl. The electron exchange correlations were treated within a generalized gradient approximation (GGA) as the PBE-scheme. In order to include the impact of valence electrons an onsite Coulomb potential is added to GGA as GGA+U. Within GGA and GGA+U, CFA shows half-metallic behaviour but FCA is metallic. The calculated values of the magnetic moment and TC are in close agreement with the experimental data.

The observation of the stimulated terahertz radiation in magnetic junctions at the room temperature resulting from the current injection of nonequilibrium spins is reported. Contacts between two ferromagnetic layers and between a ferromagnetic and an antiferromagnetic layer are investigated. As the current is increased, first, a narrow isolated radiation peak at terahertz frequencies is observed, which is analogous to the laser peak; then, the peak broadens and its intensity increases by more than an order of magnitude.

The possibility of generation of terahertz electromagnetic waves by the current in a planar structure composed of metalferromagnetic nanoparticles imbedded into an antiferromagnetic medium, is considered.

We report on apparently the first observation of terahertz stimulated radiation in magnetic junctions due to nonequilibrium spins injected by current at room temperatures. The contact between ferromagnetic layers is investigated and so the contact between ferromagnetic and antiferromagnetic layers. The current flowing in the structure creates an inversed population of spin energy levels. After a placing of such a structure in a resonator positive feedback and stimulated emission appears. When current is growing, we observe the relatively narrow (in frequencies) peak - analogous to laser generation but at terahertz frequencies. For the higher currents we observe the picture of electromagnetic turbulence.

Magnetic states in rectangular epitaxial 60 nm thick Fe (011) microstructures grown on the A-plane of sapphire with a Mo seed layer were studied by magnetic-force microscopy (MFM) and micromagnetic calculations. These micro-size elements were oriented so that the long axis was parallel or perpendicular to the easy axis of magnetization (EAM), the rectangles width was 0.1 to 8 µm and the aspect ratios (AR) were 1, 2, 4, 6 and 8. For such micro-size elements, the width to AR diagrams of magnetic states arising in the zero magnetic field were constructed using MFM and micromagnetic calculation methods. The dependence of the arising magnetic states on the microstructure size was examined.

We use superconducting rings with asymmetric link-up of current leads for experimental investigation of winding number change at magnetic field corresponding to the half of the flux quantum inside the ring. According to the conventional theory, the critical current of such rings should change by jump due to this change. Experimental data obtained at measurements of aluminum rings agree with theoretical prediction in magnetic flux region close to integer numbers of the flux quantum and disagree in the region close to the half of the one, where a smooth change is observed instead of the jump. First measurements of tantalum ring give a hope for the jump. Investigation of this problem may have both fundamental and practical importance., Comment: 8 pages, 5 figures

The stimulated emission of terahertz radiation in magnetic junctions at room temperature resulting from the current injection of nonequilibrium spins is observed. Contacts between two ferromagnetic layers as well as between a ferromagnetic and an antiferromagnetic layer are investigated. The current produces the population inversion of spin energy levels. As the system is placed in a cavity, positive feedback and stimulated emission appear. The development of a dominant emission peak and onset of electromagnetic turbulence are observed.

A spin-injection oscillator in the pulsed regime is studied for the first time at different time parameters of current pulses using an opto-acoustic transducer in the absence of chopper. The reciprocity principle is violated when the direction of current in the pulse is reversed in the pulsed regime of the terahertz generation. The radiation signal of the spin-injection emitter is proportional to the number of charges that are injected by a current pulse and does not depend on the energy that is released in the presence of the pulsed current flow.

The terahertz region of the electromagnetic spectrum (approximately 0.3–30 THz) is still insufficiently mastered primarily because of the absence of compact and controllable emitters (oscillators) and receivers (detectors) reliably operating in this range in a wide temperature range, including room temperature. The corresponding recent studies in this field, which were supported by the Russian Foundation for Basic Research, have been reviewed. New physical effects have been proposed and principles of the operation of terahertz devices based on these effects have been implemented. These effects refer to the physics of ferromagnetic and/or antiferromagnetic conducting layers assembled in micro- and nanostructures, which are called magnetic junctions. These effects are as follows: the formation of a quasiequilibrium distribution of current-injected electrons over the energy levels and the possibility of inverted population of levels, induction of the macroscopic magnetization by a spin-polarized current in an antiferromagnetic layer in the absence of external magnetic field, the appearance of current-induced contribution to antiferromagnetic resonance, and the experimental observation and study of the properties of terahertz radiation in ferromagnet-ferromagnet and ferromagnet-antiferromagnet junctions.

The spin-injection emission in a ferromagnetic junction at terahertz frequencies is theoretically analyzed. It is demonstrated that the efficiency of the emission caused by the sd-exchange interaction of the injected spin in which the electromagnetic field is involved strongly depends on the orientation angle of the magnetization of the active region relative to the magnetization direction of the injecting region. The fact that the calculated radiation frequency and power are close to the experimental results shows that the sd-exchange emission must be taken into account in the interpretation of the observed terahertz emission in magnetic junctions.

Spin-polarized current can tilt magnetic sublattices in an antiferromagnetic layer of a ferromagnet-antiferromagnet junction without imposing any external magnetic field. Thus, the current can induce magnetization in the antiferromagnetic layer. This effect seemingly took place in experiments on the observation of terahertz emission at the precession frequencies of current-induced magnetization. In this work, the mechanisms of motion of the induced magnetization, as well as the possibility of detection and generation of radiation emitted during such motion, are suggested and discussed. The notion of spin-injection antiferromagnetic resonance is introduced.

The change in the direction of the circumferential lattice magnetization by using the spin-polarized current is found by magnetic force microscopy to be possible for square epitaxial Fe (001) microstructures in the basic state. Such a change of the magnetization occurs when applying the magnetic saturation field to the structure with the subsequent switching off of the field accompanied by passing the current with the density above a certain threshold on the order 1012 A/m2 through the structure. In the basic state of the structure, the change of the magnetization depends not only on the current density but also on the spin polarization and the region of the current flow. The effect of the spin-polarized current on the circumferential magnetization of the structure, which is related to the injection of spins by the current, is discussed.

Current flow in the structure consisting of a hard-magnetic ferromagnetic rod (hardened steel) with a diameter of up to 100 μm that contacts a thin (10–100 nm) ferromagnetic (FeMn) film is studied at room temperature. Effective magnetization is induced in the FeMn film in the presence of the spin-polarized current in spite of the absence of the intrinsic magnetization. The terahertz radiation that is detected in this work is caused by the precession of the induced magnetization. The emission is interpreted using the recent theoretical predictions on the effect of the sd exchange on the lattice dynamics of antiferromagnetic layer.

A method for the measurement and identification of the radiation frequencies of the spin-injection oscillator in the terahertz frequency range using a diffraction grating is developed and experimentally implemented. For the system consisting of a ferromagnetic rod (Fe) and nanosized ferromagnetic film (Fe3O4 with a thickness of up to 100 nm), the thermal and dynamic components of the radiation that is induced by the current flow are separated. The diffraction peaks at a frequency of about 9.6 THz and a band of 37% at a level of 3 dB and at a frequency of 43.5 THz are demonstrated. It is shown that the intensity of each signal is significantly higher than the thermal background level.

The magnetic structures of Fe (001) epitaxial rectangular elements 100 nm thick, 0.25–4 μm wide aspect ratio AR 1:4 and 1:8 oriented along the easy (EAM) and hard (HAM) magnetization axes were studied by magnetic force microscopy and micromagnetic calculations. All the elements of 1 μm width and wider are in multi-domain states, which type depends on the AR and orientation with respect to EAM. In the elements oriented parallel to EAM at low AR, a diamond state realizes while at larger AR the fundamental state is of Landau type. In the elements with the orientation parallel to HAM at low AR, a cross-tie state is observed and at larger AR the states are of a concertina or a meander type. As the element sizes decrease, the domain wall width does not virtually undergo any changes and the transition from a multi-domain to a quasi-vortex state proceeds through monotonic increase of the sample volume fraction with a non-collinear magnetization distribution. The quasi-vortex state occurs at the width lower than 0.6 μm and depends neither on AR nor on the orientation with respect to EAM. The transition from a quasi-vortex to a quasi-single domain state depends on AR and orientation relatively to EAM.

The response of a ferromagnet-antiferromagnet junction to a high-frequency magnetic field is calculated as a function of the spin-polarized current density through the junction. Conditions are chosen under which the response is zero in absence of such a current. It is shown that increasing in the current density leads to proportional increase in the resonance frequency and resonant absorption. A principal possibility is indicated of using ferromagnet-antiferromagnet junction as a terahertz radiation detector.

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 taking into account) and follows the current without inertia. Efficiency of the oscillator depends strongly on the material used and quantum efficiency may exceed the unity. It means the stimulated radiation processes play an important role.

The spin-injection emission of the system that consists of a nonmagnetic conducting rod and two-layer planar heteroepitaxial structure formed by thin metal and magnetite films is experimentally studied. The electromagnetic emission in the terahertz range is demonstrated for the first time due to the creation of the nonequilibrium population of the spin energy subbands (relatively low current densities of about 105 A/cm2 are needed at room temperature).

The energy efficiency of the spin-injection emitter based on the rod-film ferromagnetic structure with a point contact between the components in the terahertz frequency range is experimentally estimated. The film material substantially affects the efficiency. A concentrator of magnetic flux is proposed for an increase in the efficiency. The experimental estimations allow the quantum yield of the emitter that is greater than unity. This result indicates significant contribution of the stimulated radiative transitions.

The generation of electromagnetic THz waves by a current is experimentally investigated in planar structures comprised of two ferromagnetic films. When the films come into contact with a thin copper rod, the current is applied to both layers. The first layer, which plays the role of an injector, polarizes the spins of the current carriers. In the second working layer, the conditions are created for spin population inversion and the generation of THz waves. At a current of 350 mA, the radiation wavelength is 16.4 THz and a power of 10 mW is reached at room temperature.

Nickel films of 170 nm thick were grown on sapphire substrates of the A, R and C orientations. Their electric characteristics and surface morphology were studied. Peculiarities of the film growth and optimum growth conditions for films of high electron mobility were determined. Nickel films grown on the sapphire A-plane with a high residual electron mean free path were found suitable for the fabrication of ballistic planar ferromagnetic nanostructures. Ballistic electron transport was observed in cross-type epitaxial Ni (111) nanostructures.

The magnetic structure of planar epitaxial microstructures Fe (0 0 1) fabricated as rectangles and crosses of 200 nm to 20 μm sizes was studied using magnetic force microscopy and micromagnetic calculations. Most characteristic micromagnetic ground states were examined. The effect of microstructure sizes and orientation, with respect to the crystallographic axes, on the magnetic structure was considered. It was found that the micromagnetic ground state is a sequence of vortices or a diamond structure and also the Landau structure when the long microstructure axis is parallel to the easy axis of magnetization (EAM). When the microstructure sizes become smaller than 0.5 μm, micromagnetic states convert to a quasisingle-domain state. In microstructures oriented along the hard axis of magnetization in the film plane, micromagnetic ground states display either a concertina structure or a sequence of vortices and antivortices. In cross-shaped microstructures, the magnetic structure of the arms of the cross was found to be similar to that observed in rectangular microstructures of the same size and orientation relative to the crystallographic axes. However, the magnetic structure of the central part of the cross is not a superposition of the magnetic structures extended from the arms. It is determined by the EAM direction.

The dependence of the anisotropic magnetoresistance (AMS) of the single-crystal Fe(001) film grown with the aid of the pulsed laser evaporation on the direction and magnitude of the external magnetic field is analyzed. Three ranges of magnetic fields with different types of variation in AMS with the direction of magnetic field are revealed. The discontinuities of resistance and the hysteresis are demonstrated in a certain range of magnetic fields. The anisotropy field is estimated using the experimental results.

A magnetic-force-microscopy investigation is conducted into the influence of the shape and magnetic anisotropy on the magnetic structure and the mode of magnetization reorientation in epitaxial iron thin films patterned by subtractive techniques. Magnetic anisotropy is found to have a strong influence on the magnetic structure. With an applied field directed along a specimen, the latter is in a single-domain state when oriented parallel to the easy axis of magnetization, and is in a multidomain state when oriented perpendicular to the easy axis, the domain magnetic moments being parallel to the easy axis in both cases. The magnetic structure appears as a streaky pattern. Magnetization reorientation proceeds by domain-wall motion in both cases. The tanks do not change the mechanism of magnetization reorientation in the rectangular part, yet they ensure a single-domain state at lower magnetic flux densities. The results should offer some scope for using epitaxial iron thin films of suitable shape and crystallographic orientation in spin-valve injectors or detectors.

Magnetoresistance of a planar single crystalline Ni nanostructures has been measured at room and liquid helium temperatures. Bending GMR effect increases from 4% under diffusive to more than 200% under ballistic electron transport in cross-type nanostructures. Magnetoresistance measured for longitudinal and transverse magnetic fields are qualitatively different and explained by a nonsymmetrical magnetic domain structure in the central part of the cross.

Growing of epitaxial Fe50Mn50/Fe/Mo/R-sapphire films was performed with a new configuration of two in-plane easy axes of Fe(001)-layer magnetization in which application of annealing in a magnetic field forms an unidirectional anisotropy. The microstructures made from these films exhibited an exchange bias 25–35 G along an exchange field generated at antiferromagnet/ferromagnet (AFM/FM) interface. Magnetic force microscopy (MFM) experiments supported by micromagnetic calculations and magneto-resistive measurements allowed interpretation of the magnetic states of the Fe layer in these microstructures. The magnetic states of the iron layer are influenced more by crystallographic anisotropy of the Fe-layer than by unidirectional exchange anisotropy.

A magnetic tunnel junction Fe3O4/MgO/Fe with (001) layer orientation is considered. The junction magnetic energy is analyzed as a function of the angle between the layer magnetization vectors under various magnetic fields. The tunnel magnetoresistance is calculated as a function of the external magnetic field. In contrast with junctions with unidirectional anisotropy, a substantially lower magnetic field is required for the junction switching.

Complementary analysis of morphology, crystal structure, electronic transport, and magnetic properties is applied to optimize the epitaxial growth of Fe(001) films with the improved electronic transport and magnetic properties. It was found that the mean free path of residual electrons and coercive forces are correlated in the epitaxial single-crystal Fe(001) films grown under different temperatures and depend on the film morphology.

Electrical resistance of a three-layer heteroepitaxial Mo(35 nm)/Nb(dNb)/Mo(35 nm) (001) film was found to exhibit oscillatory behavior as a function of thickness dNb of the ultrathin Nb interlayer. The oscillation period is equal to one Nb monolayer (0.16 nm). The resistance minimum of such a film corresponds to the interlayer thickness with a half-completed monolayer and is equal to the resistance of an individual Mo film of thickness 70 nm equivalent to the total thickness of the three-layer film. In this case, the three-layer film conducts as if it is a unified layer. The resistance of a three-layer film with completed Nb monolayers is maximum and equal to the resistance of two individual parallel-connected Mo films of half thickness (35 nm) each. These results are explained by the strong influence of the built-in potential, whose magnitude and scattering properties are periodic functions of the interlayer thickness.

The thickness dependence of the electronic conductivity of thin (5–150 nm) single-crystal (100) films of refractory metals is investigated at different temperatures ranging from 4.2 K to room temperature. Regions of square-root, quasilinear, and quadratic dependences are observed. The quasilinear thickness dependence is explained by the influence of quantum effects on the transverse motion of electrons in the case when electron scattering by the film surfaces dominates. For macroscopic film thicknesses 30–50 nm, much greater than the Fermi wavelength of an electron, quantum corrections to the electronic conductivity reach values of the order of 50%. This is a consequence of the quantum size effect for grazing electrons, which leads to an anomaly in electron scattering by the film surfaces. The region of the quadratic thickness dependence corresponds to the quantum limit, and the square-root region corresponds to the classical limit. The effect is explained in a quasiclassical two-parameter model (the effective angle α* for small-angle electrons and the parameter γ, equal to the ratio of this angle to the diffraction angle) that takes into account the diffraction angular limits for grazing electrons. The effect occurs for parameters α*≪1 and γ∼1 and differs from the “ordinary” quantum size effect.

The investigation of the growth-temperature effect on electrical conductivity, measured at room and helium temperatures, as well as on structure, defined by reflection high-energy electron diffraction measurement, of thin tungsten and niobium films, grown by laser ablation deposition on a sapphire R-plane under ultra high vacuum, was made. It was shown that for the films with thickness of 60–80 nm the residual resistance ratio (RRR), which is used as the film quality parameter, is in limits of 12–80 and 7–20 for Nb and W, respectively. It increases rapidly if the substrate temperature, at which the film is grown, exceeds 350°C due to the growth of a perfect monocrystallinc epitaxial film, which has a bec structure with the [100] axis perpendicular to the substrate plane and with the [111] axis parallel to the c axis of the substrate. The film resistivity is close to the bulk monocrystal resistivity and smoothly depends on film growth temperature while the residual film resistivity diminishes as temperature increases. Both RRR and residual film resistivity are saturated at substrate temperature greater than 400–500 °C. Such dependence can be explained by the presence of an imperfect “bulk” phase, whose concentration is low at a high film growth temperature and rapidly increases with its diminishing to lower than 400–500°C. As a result, the scattering of conducting electrons is defined by film surface scattering under low concentration of the bulk phase at high and by bulk scattering on “static” defects of the imperfect bulk phase at low growth temperatures.

Here we find the increase in 1/f noise of superconducting resonators at low temperatures to be completely incompatible with the standard tunneling model (STM) of Two Level Systems (TLS), which has been used to describe low-frequency noise for over three decades. We revise the STM to include a significant TLS - TLS interaction. The new model is able to explain the temperature and power dependence of noise in our measurements, as well as recent studies of individual TLS lifetimes using superconducting qubits. The measurements were made possible by implementing an ultra-stable frequency-tracking technique used in atomic clocks and by producing a superconducting resonator insensitive to temperature fluctuations. The latter required an epitaxially grown Nb film with a Pt capping layer to minimize detrimental oxides at all interfaces., Comment: 7 pages, 3 figures

An investigation was made of electrical properties of tungsten films of thickness in the range of 30–140 nm, grown by laser ablation deposition in ultrahigh vacuum on [1012] sapphire substrate. From the data on the size effect and the temperature dependence of the resistivity r, supported with reflection high energy electron diffraction measurements, we find that the films, deposited onto clean substrates kept at temperatures higher than 500 °C, grow epitaxially with high quality crystalline structure. The effective electron mean free path changes from 300 to 1400 nm while the residual resistance ratio RRR=r (295 K)/r (4.2 K) changes from 7 to 35. At low temperatures we find the temperature dependent part ρ(T)≊ATn, with A=1.56 mΩ cm K−n, n=3–3.4 for the temperatures T

The surface morphology of nickel thin films is investigated via atomic force microscopy. The multistage film growth mechanism is found to be dependent on substrate temperature and film thickness. It is shown that conduction electron scattering from the irregularities of the outer and inner surfaces of structures are influenced by the surface morphology and determined by an integrated contribution of the surface’s fluctuation density spectrum. The morphology influence can be decreased under certain growth conditions so that the residual mean free path of conduction electrons can reach 1000 nm, exceeding the film thickness. Epitaxial nanostructures with high electron mobility have been fabricated. Investigation of their magnetic structure has shown that their magnetic domain dimensions are less than the residual mean free path of electrons determined by the surface morphology.

Iron film growth conditions and films properties on A- and R- sapphire surfaces were investigated. The best growth conditions were achieved at temperatures about 250 - 300°C. A 10 nm Mo seed layer on the A-sapphire surface improves Fe film morphology and film roughness becomes less than 1 nm. As a result epitaxial Fe (011) films with high residual electron mean free paths (about 0.5 mkm) were grown on the A-sapphire surface. These films can be used for ballistic ferromagnetic planar nanostructures fabrication. The magnetic domain configuration of epitaxial iron nanostructures shaped as bridges and crosses depending on the orientation relative to the easy magnetic axis Fe [100] was examined. If the long side of the bridge is directed along the easy magnetic axis, the single domain structure state is easily reached up to maximum structure width about 2 mkm. A stripe domain structure can be observed when the easy magnetic axis is normal to the long rectangular structure axis. The structure orientation at some angle with the easy magnetic axis leads to a magnetic domain configuration along the easy axis is independent of the structure size down to a structure width ~0.5 mkm and depends only on the easy axis direction. The single domain state can be obtained in structures with a width less than 0.5 mkm. The cross-type structures may have only a two-fold symmetry magnetic configuration. Trapeziform domains were found in structures directed along the hard Fe magnetic axis.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

By means of magnetoresistance and magnetic force microscopy (MFM) measurements the electrical and magnetic properties of ferromagnetic strips and crosses of hybrid nanostructures Py/Mo (Py - permalloy (Ni 80 Fe 20), Mo - molybdenum) have been investigated. Unusual behaviour of the cross magnetoresistance in these nanostructures was found. The dependences of the cross resistance against external magnetic field have the image of the curves with hysteresis typical for anisotropic magnetoresistance (AMR). However, they demonstrate anomalous magnetoresistance dependence on orientation relatively to the axis of the ferromagnetic arm of the cross. In the transverse magnetic field (perpendicular to the axis of the ferromagnetic arm) magnetoresistance has two minima as for the longitudinal AMR. In the longitudinal magnetic field (parallel to the axis of ferromagnetic arm) there are two maxima, typical for the transverse AMR. The value of the effect is about one percent. The AMR of the strip has the supplementary extremes, indicated on a more complex character of magnetization reversal, depended on the shape of nanostructures. The data of the magnetoresistance measurements are compared with MFM images.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We propose and discuss the mechanisms of terahertz sd exchange radiation during transmission of the spin-polarized current in a structure from a thin steel rod pressured to an ultrathin ferromagnetic film. The two mechanisms considered are quantum transitions between the quasi-Fermi levels in the film near the rod and precession of injected spins around the film magnetization.

A technology of smooth 15 - 50 nm thin Bi-film fabrication with the surface roughness of about 1 nm using two ultrahigh vacuum film growth methods, partially ionized beam deposition (PIBD) and molecular beam deposition (MBD), was developed. The dependence of film surface morphology on the key growth parameters, deposition rate, growth temperature, film thickness, and deposited particles energy was investigated by atomic force microscopy, and optimum growth conditions were determined. In the case of PIBD method, the accelerating voltage was found to influence the surface morphology most distinctly. The most uniform and smooth films with equal size grains and minimum roughness of 1 nm were grown at the accelerating voltage 3 - 4 kV. It was also found that bismuth films grown under the optimum condition 4 kV become continuous when the film thickness is more than 10 nm. In the case of MBD method, a decrease of the growth temperature down to 40°C substantially suppresses the growth of surface hillocks and the film surface roughness is reduced down to 1 nm. The obtained results can promote developing a nanotechnology for nanowire and quantum-well structure fabrication using thin semi-metallic Bi films.

We investigated transfer resistance of single crystalline W (001) nanostructure in the temperature interval 4.2 - 295 K. It is found that the crossover from liquid - to gas-like flow electron transport takes place when electrode spacing is comparable to electron mean free path. Under diffusive electron transport both positive and negative signs of the transfer resistance are observed in the depending on the geometry of applied current. The latter is not found at ballistic electron transport. Transfer resistances change faster than liner dependence against the reversal electron mean free path.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A road map for the fabrication of epitaxial metallic electrodes, quantum dots and wires is considered for potential application in solid-state qubit technology. The nanotechnology developed includes high quality low-roughness film epitaxy, probe lithography and subtractive techniques for the fabrication of epitaxial nanostructures with a lateral resolution down to 10 nm.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We found that a ballistic planar constriction exhibits different properties in angular dependence of the magnetoresistance in compare with that of the diffusive point contact. It shows unusual two-minima angular dependence. This behavior also differs much from that of ballistic four terminal bridges, where monotonic angular dependence of the magnetoresistance is observed.