We show that сluster magnetism in ferromagnetic amorphous Fe67Cr18B15 alloy is related to the presence of large, D=150–250 Å, α-(Fe Cr) clusters responsible for basic changes in cluster magnetism, small, D=30–100 Å, α-(Fe, Cr) and Fe3B clusters and subcluster atomic α-(Fe, Cr, B) groupings, D=10–20 Å, in disordered intercluster medium. For initial sample and irradiated one (Φ=1.5×1018 ions/cm2) superconductivity exists in the cluster shells of metallic α-(Fe, Cr) phase where ferromagnetism of iron is counterbalanced by antiferromagnetism of chromium. At Φ=3×1018 ions/cm2, the internal stresses intensify and the process of iron and chromium phase separation, favorable for mesoscopic superconductivity, changes for inverse one promoting more homogeneous distribution of iron and chromium in the clusters as well as gigantic (twice as much) increase in density of the samples. As a result, in the cluster shells ferromagnetism is restored leading to the increase in magnetization of the sample and suppression of local superconductivity. For initial samples, the temperature dependence of resistivity ρ(T)~T2 is determined by the electron scattering on quantum defects. In strongly inhomogeneous samples, after irradiation by fluence Φ=1.5×1018 ions/cm2, the transition to a dependence ρ(T)~T1/2 is caused by the effects of weak localization. In more homogeneous samples, at Φ=3×1018 ions/cm2, a return to the dependence ρ(T)~T2 is observed.

The effect of laser irradiation on the structure and properties of the YBa2Cu3O7 − δ epitaxial super-conducting films (T c = 90–91 K) that are grown on the SrTiO3 and LaAlO3 substrates is studied. The films exhibit a system of pyramidal peaks that are incorporated in the single-crystal structure of the film whose system of the (00l) planes is parallel to the surface of the substrate. It is demonstrated that the peaks represent growth defects that result from the relaxation of the accumulating strain due to the mismatch of the crystallographic parameters of the growing layers of the film and substrate. The island structures that are formed owing to the relaxation of strains acquire the (11l) or (10l) orientation and penetrate through the film layers in the course of growth. It is demonstrated that the irradiation using relatively short laser pulses makes it possible to modify the structure of the dielectric clusters and allows the smoothing of the film surface at an insignificant (5–10%) decrease in the concentration of the superconducting phase. An increase in the energy density to a level of greater than 100 mJ/cm2 when the number of pulses is greater than five causes an increase in the volume of dielectric phases and the worsening of parameters.

A metastable hexagonal R-phase is revealed in polycrystalline In2O3-SrO samples, which has the form of a network made up of mesoscopic clusters (60–180 Å in size). The clusters arise from strontium-enriched regions near grain boundaries in the main cubic structure of indium oxide. It is shown that annealing in oxygen at T a ⩾ 300°C saturates dangling bonds between the R-phase and the matrix and makes the system metastable. This state shows up in the presence of (i) solitary diffuse maxima from the R-phase imposed on Debye lines from the main phase in the X-ray diffraction pattern and (ii) the electron cyclotron resonance (ECR) line with g = 1.875. In addition, the sample in this state acquires a high resistivity (ρ ∼ 106 Ω cm). Relaxation at T ⩽ 300°C after annealing at T a > 300°C disrupts bonds between the strontium-enriched clusters of the R-phase and the indium oxide matrix. This causes spatial separation of the clusters, disruption of their coherent bonds with the matrix structure, and escape of excess oxygen from the sample along grain boundaries. As a result, a new stable state forms, which is characterized by (i) a series of diffuse maxima from the R-phase imposed on lines assigned to the main phase, (ii) the presence of the ECR line with g = 2 with the line with g = 1.875 retained, and (iii) the transition of the sample to a low-resistivity state (ρ ∼ 100 Ω cm).

The growth of La0.7Sr0.3MnO3 films in magnetron plasma, in special conditions, leads to the appearance of ensembles of micron-sized spherical crystalline clusters with fractal structure, which we consider to be a new form of self-organization in solids. Each ensemble contains 105–106 elementary clusters, 100–250 Å in diameter. Interaction of the clusters in the ensemble is realized through the interatomic chemical bonds, intrinsic to the manganites. Integration of peripheral areas of interacting clusters results in the formation of common intercluster medium in the ensemble. We argue that the ensembles with fractal structure built into paramagnetic disordered matrix have ferromagnetic properties. Absence of sharp borders between elementary clusters and the presence of common intercluster medium inside each ensemble permits to rearrange magnetic order and to change the volume of the ferromagnetic phase, providing automatically a high sensitivity of the material to the external field.

We have studied the relation between clusterization in the flux of a substance and the thickness of deposited films obtained by the magnetron and pulsed laser sputtering of La0.7Sr0.3MnO3 and YBa2Cu3O7 − δ targets, respectively. No cluster formation has been observed in the case of magnetron sputtering, which is explained by a low concentration of atoms (ions) in the sputtered material flux. In accordance with calculations for the flux of non-interacting atoms, the deposited film thickness (h) exhibits exponential decrease with increasing distance (L) from the target. In the case of pulsed laser sputtering, for which the concentration of sputtered substance in the plasma is four orders of magnitude higher, the h(L) curve sharply deviates from the calculated dependence for the distances L > 6.2 cm, which is explained by the onset of intense clusterization in the laser plasma flux.

The effect of crystalline clusters formed in a laser-induced plasma on the optical properties of YBa 2 Cu 3 O 6 + x amorphous films prepared by pulsed laser deposition has been investigated. It has been demonstrated that an increase in the number of clusters leads to a gradual disappearance of interference fringes inherent in optically homogeneous media. Simultaneously, the incorporation of metallic and insulating clusters into the amorphous medium results in a decrease in the optical band gap E 0 of the YBaCuO amorphous matrix from 1.28 to 1.06 eV and a considerable decrease in the probability of interband optical transitions with charge transfer O 2 p → Cu 3 d due to the loosening of the structure and generation of local stresses. It has been revealed that there is an additional band gap E 1 , which decreases from 0.25–0.30 eV to zero values with a decrease in the optical band gap E 0 . The additional gap has been interpreted as an energy gap between localized states that belong to the valence and conduction bands. A decrease in the density of electronic states in the narrow 3 d band leads to the overlap of tails of the density of states, so that the band gap E 1 becomes negative.

We have reinforced local superconductivity in ferromagnetic Fe(67)Cr(18)B(15) metallic glasses by ion irradiation. Superconductivity in this medium appears due to the presence of large-scale layered clusters of metallic Fe-Cr phase, 150-230 Å in size, with a ferromagnetic (or superparamagnetic) Fe-rich core and nonmagnetic Cr-rich superconducting shell. Here we show that due to the intensification of concentration phase separation in the Fe-Cr clusters under ion (Ar(+)) irradiation, the volume of the superconducting phase increases from the initial 0.4-0.5% up to 7-8%. After irradiation, the resistivity jump Δρ/ρ in the temperature range T=3.1-3.6 K increases ∼14 times, reaching 19%, as compared to 1.36% for the initial sample. In the interval of T=3.1-3.6 K, the rate of resistance change reaches 79% K(-1) for the irradiated sample instead of 3.6% K(-1) for the initial sample. In the same temperature interval, the rate of magnetoresistance change increases from 3% K(-1) for the initial sample up to 70% K(-1) after irradiation.

We report on measurements of samples with nominal composition FeSe(0.5)Te(0.5), crystallized by the Bridgman method. Magnetic and transport properties of the samples were examined. The measurements confirm the coexistence of ferromagnetism and superconductivity below the superconducting transition temperature. The ferromagnetic contribution to magnetization, estimated at 10%, might be caused by the presence of ferrimagnetic Fe(7)Se(8), which occupies about 10% of sample volume. From the Andreev spectroscopy we found superconducting energy gap Delta = 2.6 meV at T = 4.2 K, and from magnetization measurements the critical temperature T(c) = 15.8 K. The critical current density in magnetic field H = 4 kOe, determined from magnetization measurements, is j(c) = (1-2) x 10(4) A/cm(2) and weakly depends on magnetic field intensity.

Preliminary results are presented concerning static properties of a small Josephson junction under the influence of strong microwave radiation. We discuss the correspondence between a Brownian particle moving in a periodic potential and superconducting phase difference in a small Josephson junction. Next, we describe an experimental method of determining the amplitude of microwave current flowing across the junction. Typical examples of static characteristics of the junction are presented, including its dynamical resistance as a function of microwave power. We discuss also the influence of an external magnetic field on the junction dynamics and show that in this case the one-dimensional Stewart-McCumber model becomes insufficient.

Using the results of magnetization measurements of LaSrMnO cluster glasses, it is shown that the concentration of frozen magnetic moments exponentially decreases with the increase of temperature. We find that temperature dependence of the order parameter q, of the form q−q(T)∼T−5/2, is universal characteristic of the investigated cluster glasses and that the barrier height Δ closely follows the quadratic relation to the temperature, Δ≈BT2.

We report the study of the magnetoresistance (MR) and resistivity as a function of temperature in epitaxial thin films of the La0.67Ca0.33MnO3 type (LCMO). The films deposited onto Y-cut of single-crystalline LiNbO3 (LNO) substrates by pulsed-laser deposition in an on-axis geometry. For comparison, the same manganite film deposited onto LaAlO3 (LAO) substrate is studied. The MR of LCMO/LNO film is found to be anisotropic and exhibits a hysteresis loops in low magnetic fields. When magnetic field is parallel to the film plane a number of jumps are observed in the MR below magnetic fields H~6 kOe. These jumps reflect the presence of pinning centers for domain walls. Evidently, a lattice deformation produced by a mismatch of lattice constants LCMO film and LNO, which lead to distortion of the film, is the origin of such strong pinning centers.

Anomalies of a variable range hopping (VRH) in amorphous LaSrMnO films containing ferromagnetic (FM) and antiferromagnetic (AFM) crystalline clusters are investigated. Anomalies are constituted, in the 190–130 K temperature interval, by an increase of the local activation energy (εa) with decreasing temperature. It is established that the increase in εa is caused by magnetic ordering of AFM clusters containing Mn3+ and Mn4+ centers participating in VRH.

We have studied the influence of YBa2Cu3O6 + x clusters formed in the plasma generated by laser ablation of a YBa2Cu3O7 − δ target on the optical transmission spectra of amorphous YBaCuO films deposited on glass substrates arranged along the direction of predominant plasma expansion in the laser plume. It is established that intense cluster formation begins in the region of rapid decrease in the film thickness, where the temperature of plasma decreases to a level at which stable atomic complexes characteristic of the target composition can form (under the experimental conditions studied, this was observed at as distance of L > 6 cm from the target). As the amount of clusters in the deposit increases, the magnitude of the interference fringes, which are characteristic of optically homogeneous media, gradually decreases and eventually almost vanishes. At the same time, features typical of the electron structure of YBa2Cu3O7 − δ appear and grow in the optical transmission spectra of the YBaCuO films, including the absorption due to free charge carriers at ℏω < 1.2 eV (characteristic of “metallic” clusters) and the minima at ℏω = 1.4 and 1.75 eV (characteristic of a dielectric state).

We have studied the effect of atomic ordering in a nanodimensional clustered structure of amorphous LaSrMnO films on the slope of the temperature dependence of resistivity ρ(T) in the regions where dρ/dT > 0. It is established that a high concentration of clusters of a “metallic” phase (C met = 9%) capable of fertromagnetic ordering leads to a giant temperature coefficient of resistivity (TCR), with its value (normalized slope) reaching (dρ/dT)/ρ = 1.6 × 104% K−1. Samples with a small concentration of such clusters (C met = 0.1%) possess paramagnetic properties and their normalized TCR decreases by three orders of magnitude to (dρ/dT)/ρ = 1.7 × 101% K−1. This behavior is explained by self-consistent changes in the atomic, magnetic, and electron subsystems.

The influence of UV laser irradiation on the physical properties of epitaxial YBa2Cu3O7-delta (YBCO) thin (< 1 mu m) films fabricated by laser ablation was studied. The samples were irradiated by a pulsed excimer laser beam at different incident energy densities E-ir <= 160 mJ cm(-2), i. e. 2-3 times below the ablation threshold of YBCO. Analysis of the sample cross-section using a transmission electron microscope (TEM) has shown that such irradiation results in a disordered layer on the top of the film. Independent confirmation of the film surface amorphization was also obtained by tunnelling experiments. Strong UV absorption in YBCO prevents further spreading of the amorphous region, which can be considered as a protective layer for the sample interior. Only a small reduction of the superconducting critical temperature T-c was observed in the irradiated samples. The transport measurements in the normal state indicate that at the interface between the disordered layer and the non-modified part of the film there exists a wide transitional region with reduced carrier concentration.

Using the x-ray diffraction method, the atomic rearrangement in amorphous La0.6Sr0.2Mn1.2O3 films is investigated at growth temperatures T-s = 20-300 degrees C. Two stages in the disorder - order phase transition are discovered. In the first stage, amorphous structure undergoes ordering at T-s = 100 degrees C up to a maximal concentration of small ( D approximate to 30 S A) clusters which occupy 90% of the total volume. In the T-s = 100-150 degrees C temperature interval, disordering in the structure and a change in short-range order prepare the onset of a second stage. In the second stage, starting with T-s = 150 degrees C, the progressive crystallization and transition from mesoscale order to long-range atomic order at T-s = 300 degrees C take place. It is shown that all transitions produce changes in the conductivity mechanisms and magnetic properties of the films.

The properties of Josephson junctions of d-wave superconductors, characterized by unusual, non-sinusoidal current-phase relationship (CPR) have been actively investigated in recent years. Less attention has been paid to collective effects arising in systems composed of several d-wave junctions. Extension of the analysis to d-wave junctions reveal some interesting features, such as anomalous periodicity of critical current, and the appearance of frustration effects in junction arrays even in zero external magnetic fields. In this context, we investigate the properties of multi-junction superconducting quantum interferometers composed of d-wave junctions: the possible appearance of additional system phase states, the dynamical behavior and energy relationships of the system and compare these results with those relating to the systems involving s-wave junctions, characterized by sinusoidal CPR. A crucial step in the analysis is accounting for the orientation of the superconducting crystallites with respect to the interfaces. Switching between the phase states of multiple grain boundary junction systems with random grain orientation can result in additional 1/f noise in granular high-Tc superconductors.

The pressure, magnetic-field, and excess manganese effects on transport and magnetoresistance effect (MRE) are studied in both epitaxial films and bulk ceramics of the manganites (La0.7Ca0.3)1−xMn1+xO3−y (x=0–0.2). A comparison of the electrical behavior in both kinds of samples of similar composition at hydrostatic pressures of up to 1.8GPa and in magnetic fields of up to 8kOe is performed. The pressure and magnetic-field effects are shown to increase with increasing manganese content. Experimental data show that the effects of pressure and magnetic field on the temperatures of both the metal-insulator transition (TMD) and the MRE peak (TMR) are considerably stronger in the films than in the ceramics. The hydrostatic pressure increases TMD and TMR. It was shown that for both types of samples the magnetoresistance effect is affected in opposite ways by pressure and magnetic field. A direct correlation is established between TMD and conductivity bandwidth as well as between MRE and concentration of charge carriers at applied pressure. The differences in the values of pressure effect on resistance, MRE and TMD temperature in the films and ceramics are connected with both granular structure of ceramics and the oxygen nonstoichiometry in ceramic and film samples of the same content as well as with the film strain induced by lattice mismatch between the film and the substrate. The origin of pressure-magnetic-field effects is analyzed in the framework of the double exchange interaction and the small polaron hopping and variable-range hopping models.

The evolution of the cluster structure in amorphous LaSrMnO films as synthesis temperature Ts increases from 20 to 300°C is considered. Two order-disorder phase transitions with different scale parameters are observed. One of them, the aggregation of disordered atoms into small (∼20 Å) amorphous clusters at Ts = 100°C, shows up as a sharp increase in the intensity of diffuse X-ray scattering (diffuse halo 1) with a simultaneous suppression of incoherent (background) scattering. At Ts > 150°C, disordering dominates (Iincoh = Imax) until the next stage of ordering sets in at Ts = 250−300°C. At this stage, the crystalline phase forms from large (>100 Å) crystalline clusters. This amorphous-crystalline phase transition is characterized by the appearance of Debye lines and a reduction of the halo intensity. The structural phase transition to long-range order is accompanied by a decrease in the LaSrMnO resistivity from 1010 to 10 Ω cm and a change from the tunneling mechanism of conductivity involving metallic clusters (which is typical of granulated systems) to the hopping mechanism with a hop variable length following the Mott law ρ ∼ exp(T−1/4). In the magnetic subsystem, the paramagnetic-ferromagnetic phase transition occurs.

The structure, electrical, and magnetic properties of epitaxial LaCa(Sr)MnO single crystal films with a clustered structure have been studied. In films with a “metallic” phase content C m 0 ≤0.15, the electric conductivity is determined by the spin-dependent tunneling of charge carriers between “ metallic” clusters, and the magnetoresistance is maximum at T = 4.2 K. The correlated motion of carriers over the system of tunneling-linked clusters leads to the formation of a window in the Coulomb blockade. The interactions between atomic, magnetic, and electron subsystems increase in the vicinity of the dielectric-metal percolation transition ( T = 200–210 K), where the metal phase content C m in the samples with C m 0 ≥0.2 reaches a maximum ( C m crit = 0.5) due to an increase in the cluster size upon cooling. In this case, the magnetoresistance exhibits a maximum at T = 260 K, on the dielectric side of the percolation transition. Due to the presence of space charge regions at the periphery of the clusters, the content of a ferromagnetic phase is 1.5–2 times that of the “metallic” phase. For this reason, the calculations are performed using a model combining the tunneling conductivity mechanism with the percolation approximation for the description of magnetization. Allowance for the Coulomb interaction between charge carriers and clusters improves the agreement of theory and experiment.