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Samples of oxypnictide compound LaO1−x F x FeAs, with x=0.15 and 0.2 corresponding to over- and highly over-doped compositions, respectively, were prepared by solid-state reaction. We present their characterization by XRD and HRTEM, as well as resistivity ρ(T), magnetization M(B) and microwave modulated absorption (MMA) response between 4.2–300 K and applied fields B=0–8 T. With change in x, both the superconducting and magnetic behavior of the samples shows an interesting pattern. The “magnetic anomaly” at T∼130 K, observed in M(T) for x=0, instead of getting totally suppressed shows a tendency to reappear in x=0.2 sample. Both samples typically show ρ(300 K)>2.8×10−3 Ω cm and critical current density J c(5 K, 1 T)

Magnetic susceptibility, χ ( T ), is investigated in ceramic La 1− x Sr x Mn 1− y Fe y O 3 (LSMFO) samples with x =0.3 and y =0.15−0.25. A ferromagnetic (FM) transition observed in LSMFO is accompanied with an appreciable decrease of the transition temperature with increasing y , which is connected to breaking of the FM double-exchange interaction by doping with Fe. Strong magnetic irreversibility, observed in low ( B =10 G) field, gives evidence for frustration of the magnetic state of LSMFO. The FM transition, which is expanded with increasing B , is more pronounced in the samples with y =0.15–0.20 and broadens considerably at y =0.25, where the irreversibility is increased. Well above the transition, χ ( T ) exhibits a Curie–Weiss asymptotic behavior, yielding very large values of the effective Bohr magneton number per magnetic ion, incompatible with those of Mn or Fe single ions. At y =0.15 and 0.20 a critical behavior of χ −1 ( T )∼( T / T C −1) γ in the region of the FM transition is characterized by influence of two different magnetic systems, a 3D percolative one with γ = γ p ≈1.8 and T C = T C (p) , and a non-percolative 3D Heisenberg spin system, with γ = γ H ≈1.4 and T C = T C (H) , where T C (p) T C (H) . At y =0.25 the percolative contribution to the critical behavior of χ ( T ) is not observed. T he dependence of χ on T and y gives evidence for phase separation, with onset already near the room temperature, leading to generation of nanosize FM particles in the paramagnetic host matrix of LSMFO. The ferromagnetism of LSMFO is attributable to percolation over the system of such particles and generation of large FM clusters, whereas the frustration is governed presumably by a system of smaller weakly-correlated magnetic units, which do not enter the percolative FM clusters.

Magnetic and luminescent properties of ZnSe crystals doped with Fe by various methods are studied. It is established that Fe impurity is responsible for photoluminescence (PL) bands at 980, 1320, 1450 nm and quenches PL band at 630–645 nm. It is found that magnetic properties of ZnSe:Fe crystals are sensitive to the doping method. At low fields, two magnetic subsystems may be observed for the samples doped with Fe during the growth process—weak paramagnetic subsystem and antiferromagnetic subsystem with T С =–130 K. For the samples doped with Fe by high-temperature annealing in Zn melt, few magnetic subsystems may be distinguished, however, the magnetic properties are typical for spin glasses with the transition temperature T sg =(45–50) K.

A low temperature transverse thermal magnetoconductance of metals and semimetals is treated theoretically. It is shown that its high magnetic field behavior is determined by the characteristic time τɛ of jumps from one cyclotron circle to another due to electron-phonon collisions rather than by the transport time τtr that determines the conductance. The phonon-electron drag contribution to the magnetoconductance is also discussed.

Superconductivity in a LaOFeAs system is known to get introduced by F-doping (LaO1−xFxFeAs) even under ambient conditions and oxygen deficiency (LaO1−xFeAs) under high pressure conditions. Hitherto unreported, superconductivity in F-free undoped LaOFeAs samples is observed and confirmed for the first time by various characterization tools–resistive ρ(T,B), magnetic M(T,B) and modulated microwave absorption (MMA) measurements. The ρ(T) at B=0 shows a clear superconducting transition with an onset at Tcon∼17 K and a tail-like behavior when R goes to zero at Tc0∼8 K. In the presence of B, the superconducting transition shifts to lower T with a rate ∼−5.5 and −1.65 T/K, depending on whether the ρ(T) has dropped to 90% or 5% of its normal state value, respectively. M(T) in zero field cooling at B=10 mT shows diamagnetic downturn below at ∼12 K. At T Tc0, indicating the presence of weak link superconducting networks in the sample. The sample shows a complex electrical and magnetic behavior in the normal state. For instance, ρ(T) reveals a weak SDW-like anomaly at T∼132 K along with a resistivity minimum at Tmin ∼78 K. M(T) also shows the presence of a magnetic anomaly at T∼130 K. Both below and above Tcon, presence of an additional ferromagnetic component is observed in the isothermal M(B) loop measurements. The superconducting and normal state features of our sample are compared with other undoped and doped LaOFeAs systems reported in the literature.

Persistent photoconductivity is observed in ZnO single crystals and ceramics together with persistence of electron paramagnetic resonance (EPR) spectra of defects and impurity centers. It is shown that when the light is switched on and off the microwave conductivity detected from absorption of the microwave field is well correlated with the dc-conductivity measured with electrical contacts applied to the sample. The microwave photoconductivity arises together with light-induced EPR spectra and persists after switching off the light. Coexistence of the conductivity and EPR spectra shows that the photoexcited electrons cannot return back to paramagnetic centers. The persistent photoconductivity in ZnO ceramics is large in comparison with the effect observed in powders prepared from the same material and in ZnO single crystals. This suggests that surface conductivity is the dominant mechanism of persistent photoconductivity in ZnO.

Hall effect and flux pinning in YBa 2 Cu 3 O 6 + x (YBCO) thin films doped with BaZrO 3 (BZO) nanoparticles is investigated. The results show that sign reversal of the Hall coefficient from positive hole-like to negative electron-like occurs in vortex-liquid regime of undoped and BZO-doped YBCO films. With increasing BZO concentration the amplitude of the negative Hall effect is suppressed while the temperature position of the anomalous Hall effect does not depend significantly on doping level. In addition, it is shown that Hall conductivity increases non-monotonically with increasing BZO doping. These results support a model where BZO at low doping concentration induces point pinning centres turning to strong columnar pinning defects in films doped with 4% BZO.

The transport properties of GaAs/Mn/GaAs/InxGa1 − xAs/GaAs structures with a layer that is separated from the quantum well and contains Mn impurities in the concentration range 4–10 at % corresponding to the reentrant metal-insulator transition observed in the bulk GaMnAs material [17] have been investigated. The hole mobility in the objects under investigation is more than two orders of magnitude higher than the known values for the GaMnAs semiconductor and GaMnAs-based magnetic heterostructures. This makes it possible to observe Shubnikov-de Haas oscillations, which confirm a two-dimensional character of the hole energy spectrum. The calculated Curie temperature for heterostructures with indirect exchange interaction through a two-dimensional hole channel is in good agreement with the position of the maximum (at 25–40 K) in the temperature dependences of the electrical resistance of the channel. This suggests that two-dimensional holes play an important role in ferromagnetic ordering of the Mn layer under these conditions. The observations of a negative spin-dependent magnetoresistance and an anomalous Hall effect, whose magnitude correlates well with the results of theoretical calculations for two-dimensional ferromagnetic systems based on III-Mn-V, also indicate a significant role of the two-dimensional channel in ferromagnetic ordering.

Superconducting YBa2Cu3O6+x (YBCO) films are grown by pulsed laser deposition (PLD) in the orientation where its c-axis is lying in the plane of the film using (110) oriented SrTiO3 (STO) substrates with PrBCO template layer. By optimization of deposition temperature and rate the easily formed (103) orientation was avoided to get smooth and completely (110) oriented YBCO films. To improve the superconducting properties, we have also optimized the BaZrO3 (BZO)-doping in the (110) YBCO films. This gives the possibility to apply the current along the YBCO CuO2 planes where the critical current is much higher in thin film multilayers or to investigate the anisotropy and the effect of BZO pinning structure in different film orientations.

We report the effect of 4 wt% BZO-doping in GdBCO thin films on (100) STO substrates with novel nanograined target materials deposited by pulsed laser deposition (PLD) method. X-ray diffraction, atomic force microscopy and magnetization measurements, which were made in particularly wide temperature and magnetic field range, were used to determine the structural and superconducting properties. The results were compared with ones of YBCO. The deposition temperature, T s, is not very critical for GdBCO and it is found to be much lower in undoped and BZO-doped GdBCO than in YBCO. The BZO-doping of GdBCO enhanced the field dependence of critical current density, j c, at low temperatures. Furthermore, BZO-doping enhances the accommodation field, B* , below 60 K being clearly higher at 10 K in doped GdBCO than in YBCO. The pinning mechanism in GdBCO was concluded to be similar to that of YBCO. Our results clearly show that undoped and BZO-doped nanophase GdBCO is a very promising target material for applications as well as for coated conductors.

The Hall effect is investigated in oriented single crystals of a new diluted group II-V semiconductor p-CdSb doped with 2 at% of Ni in the temperature interval of T = 1.5–300 K and pulsed magnetic fields up to B = 25 T. A non-linear dependence of the Hall resistivity, ρH, on B is observed, which is strongly pronounced below ∼10 K and still exists even up to 300 K. From the analysis of ρH(B) a positive normal, ρN = R0B, and a negative anomalous, ρA, contributions are obtained. The normal Hall coefficient, R0, is determined presumably by activation of holes into the valence band, accompanied with a minor contribution of itinerant holes from the acceptor band at lowest T, whereas ρA below ∼77 K scales with resisitivity approximately as ρn (n = 1.6 ± 0.1). The anomalous contribution to the Hall effect is attributable to presence of magnetic Ni1–xSbx nanoclusters, which have been found previously from investigation of magnetic properties of p-CdSb:Ni. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Hopping conductivity in single crystals of the group II-V anisotropic diluted magnetic semiconductor p-CdSb:Ni, oriented along the [100] (# 1), [010] (# 2) and [001] (# 3) axes, is investigated in zero and pulsed magnetic fields B. At B = 0 the Mott variable-range hopping (VRH) conductivity is observed in # 2, and the Shklovskii-Efros VRH conductivity in # 1 and # 3 at T ≤ 2.5 K. However, in weak fields of B < 6 T temperature dependence of the resistivity gives evidence for the Mott VRH conductivity in # 1 below ∼ 4.2 K, whereas in # 2 and # 3 the nearest-neighbour hopping (NNH) conductivity is observed between 3–4.2 K and between 1.5–4.2 K, respectively. Eventually, in high magnetic fields of B up to ∼ 15 T and T ≤ 4.2 K only the NNH conductivity is observed in all investigated samples. The analysis of the resistivity data yields the set of microscopic parameters, such as the localization radius, the widths of the Coulomb gap and of the impurity band, the density of the localized states and the anisotropy coefficients, as well as the values of the acceptor concentration and the dielectric permittivity. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dilute magnetic semiconductors based on manganese-doped Zn0.9Cd0.1GeAs2 solid solution with various doping levels were synthesized. Their Curie point in 5-T magnetic field was 349 K. Ferromagnetic ordering in these semiconductors was due to MnAs nanoclusters, whose sizes were 3.7–3.8 nm.

The purpose of this study is to describe patients' experiences of the quality of care received at a radiotherapy centre. The data were collected using the Good Nursing Care Scale For Patients (GNCS/P), which was modified for this study. Structured questionnaires were handed out in March-May 2004 to 150 adult curative cancer patients attending outpatient radiotherapy at a university hospital in Finland. A total of 135 completed questionnaires were returned. The patients were generally satisfied with the quality of care they received. Among the four quality categories, the highest ratings were given to staff characteristics, and the lowest to the environment. Younger patients, employed patients and those with a higher level of education gave the lowest quality ratings. Improvements are needed primarily in the counselling and education of patients and their relatives. The results of this study provide valuable clues for improving the quality of care in radiotherapy based on patients' expectations.

Light-induced changes of the hysteresis loops of magnetization and microwave absorption are investigated in low-doped La1−xCaxMnO3 (x

Angular dependence of the resistivity, the irreversibility field and the critical current of undoped and BaZrO 3 -(BZO)-doped YBa 2 Cu 3 O 6+ x (YBCO) thin films are investigated using pulsed magnetic fields up to 30 T. Doping with BZO forms a dense network of anisotropic c -axis oriented columnar defects, which lead, in comparison with undoped material, to clearly improved values of the pinning potential, the critical current density and the irreversibility field in the whole angular range. The results are explained by point defect scaling theory using a renormalized anisotropy parameter in connection with linear defects. In oblique magnetic field a porous vortex matter is formed by means of kinks on the columnar defects. Our results demonstrate the efficiency of the columnar defects in thin YBCO films in magnetic fields much above the matching field, opening up a possibility to use this material in various high field applications.

The field and temperature dependences of the magnetization of GaAs/δ〈Mn〉/GaAs/InxGa1 − xAs/GaAs quantum wells with the δ〈Mn〉 layer separated from the well by a 3-nm GaAs spacer have been studied in the temperature range of 3–300 K in a magnetic field up to 6 T. An external magnetic-field-induced phase transition to a ferromagnetic state with a magnetization hysteresis loop shifted from a zero magnetic field has been found to occur at a temperature below 40 K. A theoretical model is proposed that implies the coexistence of ferromagnetically and antiferromagnetically ordered regions within the GaAs layers.

We present results of magnetic and transport measurements of GaAs/Ga1–xInxAs/GaAs quantum well structures containing a Mn δ-layer separated from the quantum well by a 3 nm spacer. The kink observed in temperature dependence of the sample resistance and anomalous Hall effect give a hint for carrier spin polarization. Magnetization measurements show an unusual shifted hysteresis loop. The observed results are treated in the frame of long range fluctuation potential model. Parameters of the potential are estimated. It is shown that disorder determines the structural properties in spite of the hole mobility of about 2000 cm2/(V·s) being much higher than in presently known ferromagnetic two-dimensional structures. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The temperature dependences of the magnetic susceptibility χ(T) and the electrical resistivity ρ(T) of ceramic samples of La1 − xCaxMnO3 with x = 0.67 (LCMO) and La1 − xCaxMn1 − yFeyO3 with x = 0.67 and y = 0.05 (LCMFO) are investigated in magnetic fields B = 50–105 G and the temperature range T = 4.2–400 K. Both samples undergo a transition from the paramagnetic state to a state with charge (orbital) ordering (CO) at temperatures TCO ≈ 272 K for LCMO and TCO ≈ 222 K for LCMFO. The behavior of the paramagnetic phase in the temperature range 320–400 K for LCMO and 260–400 K for LCMFO is described by the Curie-Weiss law with effective Bohr magneton numbers peff = 4.83 μB (LCMO) and 4.77 μB (LCMFO), respectively. The disagreement between the observed positive Weiss temperatures (θ ≈ 175 K (LCMO) and θ ≈ 134 K (LCMFO)) and negative Weiss temperatures required for the antiferromagnetic ground state can be explained by the phase separation and transition to the charge-ordered state. The magnetic irreversibility for T < TCO is accounted for by the existence of a mixture of the ferromagnetic and antiferromagnetic phases, as well as the cluster glass phase. At low temperatures, doping with iron enhances the frustration of the system, which manifests itself in a more regular behavior of the decay rate of the remanent magnetization with time. The temperature dependence of the electrical resistivity in the range of the charge-ordered phase conforms to the variable-range hopping model. The behavior of the electrical resistivity is governed by the complex structure of the density of localized states near the Fermi level, which includes a soft Coulomb gap Δ = 0.464 eV for LCMO and 0.446 eV for LCMFO. It is established that the ratio between the localization radii of charge carriers a for LCMFO and aund for LCMO is a/aund = 0.88.

Single crystals of the solid solutions CdGeAs2:Mn(x) and Cd0.964Zn0.036GeAs2:Mn(x) have been grown by the vertical Bridgman method. An X-ray diffraction study has demonstrated that Cd0.964Zn0.036GeAs2 (I), Cd0.964Zn0.036GeAs2:Mn (1.5 wt%) (II), and Cd0.964Zn0.036GeAs2:Mn (2.18 wt %) (III) retain the CdGeAs2 structure (tetragonal system, space group I\(\bar 4\)2d). The unit cell parameters of the solid solutions are as follows: a = b = 5.934(1) A, c = 11.219(2) A for I; a = b = 5.919(1) A, c = 11.204(2) A for II; and a = b = 5.918(1) A, c = 11.208(2) A for III. Many of Mn atoms in II and III occupy interstitial sites in the crystal lattice. Selected electrical and magnetic properties of single crystals of CdGeAs2:Mn(x) are discussed.

The possibility of temporally stable nanolocalized charging of thin SiO2 layers with embedded silicon nanocrystals (nc-Si) is demonstrated. The local charge writing and reading in SiO2 layers were performed using the electrostatic force microscopy (EFM) technique under the probe of an atomic force microscope. The nc-Si inclusions in a 12-nm-thick SiO2 layer were obtained using the implantation of low-energy (1 keV) Si+ ions, followed by annealing in a nitrogen atmosphere containing 1.5% oxygen. This regime of nc-Si formation significantly improved the structure of nanocrystalline inclusions, which ensured the charge localization on a record level and retention for a prolonged time: the diameter of charged regions in SiO2 layers with nc-Si inclusions did not exceed 35 nm, while the charge storage time reached tens of hours. The localized EFM charging can be used as a basis of the charge nanolithography on oxide layers.

Radiation hardness up to 10 16 n eq /cm 2 is required in the future HEP experiments for most inner detectors. However, 10 16 n eq /cm 2 fluence is well beyond the radiation tolerance of even the most advanced semiconductor detectors fabricated by commonly adopted technologies: the carrier trapping will limit the charge collection depth to an effective range of 20–30 μm regardless of depletion depth. Significant improvement of the radiation hardness of silicon sensors has been taken place within RD39. Fortunately the cryogenic tool we have been using provides us a convenient way to solve the detector charge collection efficiency (CCE) problem at SLHC radiation level (10 16 n eq /cm 2 ). There are two key approaches in our efforts: (1) use of the charge/current injection to manipulate the detector internal electric field in such a way that it can be depleted at a modest bias voltage at cryogenic temperature range (⩽230 K); and (2) freezing out of the trapping centers that affects the CCE at cryogenic temperatures lower than that of the LN 2 temperature. In our first approach, we have developed the advanced radiation hard detectors using charge or current injection, the current injected diodes (CID). In a CID, the electric field is controlled by injected current, which is limited by the space charge, yielding a nearly uniform electric field in the detector, independent of the radiation fluence. In our second approach, we have developed models of radiation-induced trapping levels and the physics of their freezing out at cryogenic temperatures. In this approach, we intend to study the trapping effect at temperatures below LN 2 temperature. A freeze-out of trapping can certainly help in the development of ultra-radiation hard Si detectors for SLHC. A detector CCE measurement system using ultra-fast picosecond laser with a He cryostat has been built at CERN. This system can be used to find out the practical cryogenic temperature range that can be used to freeze out the radiation-induced trapping levels, and it is ready for measurements on extremely heavily irradiated silicon detectors. Initial data from this system will be presented.

Substitutional studies have been carried out on sintered bulk samples of YBCO to determine the effect of doping it with Pr, Ca (at Y site) and Ni (at Cu site) in small concentrations on the formation of effective pinning centres for jc enhancement. The results show Pr and Ca substitutions to be far more effective than Ni substitution. The former two give rise to formation of rows of oxygen vacancies with pronounced strain fields in CuO2 planes where superconductivity resides. The defects thus formed seem to be analogous to arrays of normal nanodots in CuO2 planes which are expected to have strong intragrain pinning interactions with pancake vortices of CuO2 planes forming the mixed state structure. Both these substitutions tend to marginalize the adverse effects of grain boundaries. The superconducting volume fraction of the pristine sample is significantly raised by both these substitutions. These special features are, however, absent with Ni substitution. This paper brings out the importance of Pr substitution in significantly enhancing jc(B).

We report the synthesis, high-resolution micro-structure, magneto-transport and magnetization of nano-diamond doped MgB2?nDx with x = 0.0?0.1. The superconducting transition temperature (Tc) is not affected by x up to x = 0.05, indicating that the added nano-diamond (1) does not decompose to C and (2) does not partially substitute for B in MgB2. R(T) versus H measurements show higher Tc values under the same applied magnetic field for the nano-diamond added samples, resulting in higher estimated Hc2 values. Isothermal magnetization measurements show that above 2?T, the critical current density (jc) is of the order of 105?A?cm?2 for the pristine sample. jc is further increased to three times for 3% nano-diamond doped samples. High-resolution transmission electron microscopy (HRTEM) observations clearly show the dispersion of nano-diamond particles, with an average particle size of 8?10?nm, in the MgB2 matrix. It seems likely that the dispersed nano-diamond particles of below 10 nm in size are acting as effective pinning centres responsible for improving the superconducting performance of the parent MgB2.

Thin YBa2Cu3O6+x (YBCO) films are prepared by pulsed laser deposition (PLD) from pure micro- (mu) and nanocrystalline (n) targets and a n-target optimally doped with 3.9 wt% BaZrO3 (BZO). Effects of target grain size and doping on superconducting (SC) properties of the films are investigated using a SQUID magnetometer up to 5 T and transport measurements in pulsed magnetic fiefds up to 30 T. In comparison with mu-films, clearly increased values of jc are observed in n-films. Optimal doping with BZO still increases this difference in high magnetic field range and lengthens the low-field plateau of jc(B) and increases the accommodation field B* which are typically around 110 mT, 160 mT and 500 mT at 5 K in mu-, n- and BZO-doped films, respectiveiy. Transport measurements at T > 65 K show significant improvement of irreversibiiity line (IRL) and jc(B) in films prepared from n-target and BZO-doped target. These improvements of the superconducting properties in high magnetic fiefds make pure and BZO-doped n-films attractive for high field applications.

The magnetic-field dependences of the Hall coefficient and transverse magnetoresistance are studied experimentally and theoretically in p-Bi2Te3 crystals doped heavily with Sn and grown by the Czochralski method in the case of both classical and quantizing magnetic fields as high as 12 T with the magnetic-field orientation along the C 3 trigonal axis. The Shubnikov-de Haas effect and quantum oscillations of the Hall coefficient were measured at temperatures of 4.2 and 11 K. The six-ellipsoid Drabble-Wolfe model of the energy spectrum and the magnetic-field dependence of the Hall coefficient are used as the basis for the method for determining the Hall factor and Hall mobility. New evidence is obtained in support of the existence of the narrow band of impurity Sn states occupied partially with electrons against the background of the light-hole band spectrum. The parameters of impurity states are estimated including their energy (E Sn ≈ 15 meV), the broadening (Γ « kT), and the radius of localization of the impurity state (R ≈ 30 A).

The influence of the replacement of Mn ions in the La0.7Ca0.3Mn1 − y Fe y O3 compounds (0 ≤ y ≤ 0.09) by another transitional metal, Fe, was studied. The radii of both ions are almost identical, which makes the effect of the transitional metal on the physical properties of manganites more transparent. The crystal structure of three samples (with y = 0, 0.03, 0.09) is studied in the temperature range T = 1.5–300 K by neutron powder diffraction. All investigated samples belong to the orthorhombic space group Pnma (62). It is confirmed that Fe ions occupy the Mn positions in the unit cell. As the Fe concentration increases, the saturation value of the spontaneous magnetic moment and the Curie temperature decrease, but the ground state remains ferromagnetic for 0 ≤ y ≤ 0.1. The saturation values of the magnetic moments at T = 1.5 K are m FM = 3.72(3), 3.40(3), and 3.27(3) μ B /Mn for the samples with an Fe concentration y = 0, 0.03, and 0.09, respectively.

There are two key approaches in our CERN RD 39 Collaboration efforts to obtain ultra-radiation-hard Si detectors: (1) use of the charge/current injection to manipulate the detector internal electric field in such a way that it can be depleted at a modest bias voltage at cryogenic temperature range (⩽150 K), and (2) freezing out of the trapping centers that affects the CCE at cryogenic temperatures lower than that of the liquid nitrogen (LN 2 ) temperature. In our first approach, we have developed the advanced radiation hard detectors using charge or current injection, the current injected diodes (CID). In a CID, the electric field is controlled by injected current, which is limited by the space charge, yielding a nearly uniform electric field in the detector, independent of the radiation fluence. In our second approach, we have developed models of radiation-induced trapping levels and the physics of their freezing out at cryogenic temperatures.

Electron paramagnetic resonance (EPR) of the triplet centers and dynamic 29Si nuclear polarization was studied in irradiated naturally abounded (4.7%) and 29Si isotope enriched (99.3%) silicon crystals. Saturation of the EPR lines of the photoexcited triplet centers with nonequilibrium spin polarization between mS = +1, 0, and –1 sates leads to the nuclear polarization ≈7000 times higher than equilibrium value. It was shown that the observed dynamic nuclear polarization is a result of the “solid-effect”. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The structural, electrical, and magnetic properties of ceramic perovskite manganites LaMnO3 + δ (δ = 0–0.154) are investigated. It is found that, in a weak magnetic field (B = 2 G), the LaMnO3 + δ manganite with δ = 0.065 at temperatures below the Curie temperature T C of the paramagnet-ferromagnet phase transition has a mixed (spin glass + ferromagnet) phase. In LaMnO3 + δ manganites with the parameter δ = 0.100–0.154, this phase transforms into a frustrated ferromagnetic phase. A similar transformation was observed previously in La1−x CaxMnO3 compounds at calcium contents in the range 0 ≤ x ≤ 0.3. This similarity is explained by the fact that, in both materials, the Mn4+ concentration and, accordingly, the hole concentration c change equally in the concentration range from ∼0.13 to 0.34 with an increase in x or δ. However, the magnetic irreversibility, the concentration dependences of the Curie temperature T C(c) and the magnetic susceptibility X(c), and the critical behavior of the temperature dependence of the susceptibility X(T) in the vicinity of the Curie temperature T C differ substantially for these two materials. The observed differences are associated with the distortion of the cubic perovskite structure, the decrease in the degree of lattice disorder, and a more uniform distribution of holes in the LaMnO3 + δ manganites as compared to the La1 − x CaxMnO3 compounds.

Superconducting parameters of different, almost 20 years old Y–Ba–Cu–O samples, prepared in 1987–1988 are investigated. The aim of this research is to find out how a heavy ion beam can enhance the superconducting features of very old and originally not always perfect Y-based specimens. As is observed, their electrical and magnetic characteristics are very sensitive to high-energy Bi-ion irradiation, which results in significant increase of the superconducting parameters. The most important one of them is the global critical current density which is calculated with the help of a new method on the basis of experiments. It can be increased by 18–39%, depending on the original, starting conditions of the samples before the irradiation. At the same time, the average values of intragrain critical current density grows by 37–51%. A slight increase in the critical temperature of 1–2 K was also observed. The experiments on AC susceptibility demonstrate that this irradiation causes to develop faster the total diamagnetic state and decreases the loss. The reason of these effects can be found in the better orientation of crystals, enlargement of microcrystalline aggregates, higher homogenization of the material, thus, in the increase of the superconducting component of samples due to the irradiation.

Formation of a natural oxide in ambient atmosphere of the mirrors of a GaSb/GaInAsSb/Ga0.1Al0.9As0.93Sb0.07 laser heterostructure at places of emergence Al-rich layers on the mirror surface is studied. The evolution of topography of the laser mirrors produced by cleavage under ambient and ultrahigh vacuum conditions was studied by AFM and STM for mirrors cleaved. The oxidation of Ga0.1Al0.9As0.93Sb0.07 layers on the mirror surface was monitored for more than a year. It is shown that the oxide layer develops over the course of several months and then attains a constant thickness of about 1 μm. In the course of natural oxidation, the volume of the oxide layer increases, which results in its protrusion above the laser mirror surface approximately by a third of the total thickness of the oxide formed. Ultrahigh vacuum studies ruled out the previously assumed occurrence of the effect of plastic extension of Al-rich layers at the instant of cleavage and the resulting protrusion over the cleavage plane. At the initial stage of oxidation, the oxide protruding above the surface demonstrates an unusual concave region in the upper part, which disappears as the oxide grows further. An explanation of the observed transformation of the shape of the oxide layer is offered. It is assumed that the chemical composition of the oxide varies as its thickness increases.

The temperature dependence of the resistivity, ρ, of ceramic LaMnO3+δ with δ = 0.065 and 0.154 (or simply # 065 and # 154), is investigated under hydrostatic pressure, p, between the temperatures T = 80 and 320 K in magnetic fields up to 10 T. The data for ρ(T) are analysed within a Shklovskii–Efros-like variable-range hopping conductivity model, governed by a soft Coulomb gap, Δ, and a rigid gap, γ, in the density of localized states. The validity of this approach to the resistivity of LaMnO3+δ under ambient pressure was established in recent investigations (Laiho et al 2005 J. Phys: Condens. Matter 17, 105). In the present work it is shown that upon increasing p up to 11 kbar (# 154) and 13 kbar (# 065) the magnetic Curie temperature, TC, is increased by ~12–13%. Correspondingly, Δ(p) is decreased by ~7–8% and γ(p) by ~8% in # 154 and 12% in # 065. Similarly, the electron localization radius a(p) is increased by ~4% in # 154 and 8% in # 065, respectively. The influence of pressure on TC, Δ, γ and a is interpreted by increasing the electron bandwidth and decreasing the polaron potential well, which stimulates the delocalization of electrons when p is increased.

InSb samples containing 0.22–1.42 wt % manganese were synthesized and identified. The unit cell parameter decreased as the manganese concentration increased. The samples contained microinclusions of manganese antimonides. Electrical and magnetic measurements showed two ferromagnetic phases (In1−xMnxSb solid solution with Tc ∼ 7 K and MnSb with Tc ∼ 580 K) and a ferrimagnetic phase (Mn2Sb). The samples had p-type conductivity with a charge carrier concentration of about 1020cm−3. The semiconductor conductivity was observed at low temperatures and changed to the metal conductivity with temperature elevation.

The Hall effect, electrical conductivity and electron mobility are investigated at temperatures between 55 and 500 K in n-ZnSe crystals doped with Cu, Ag or Au. The presence of a small amount of Cu atoms leads to an inversion of the sign of the Hall coefficient at temperatures above 300 K. Anomalous temperature dependence of the electron mobility is observed in the samples with low Cu concentration (

YBCO films were prepared by pulsed laser deposition from nanocrystalline targets doped with different concentrations of BaZrO3 ranging from c = 0.9 to 9.0 wt%. The critical temperature of the films decreases almost linearly with increasing BaZrO3 content whereas the critical current density shows a maximum near 3.9 wt%. In comparison with undoped YBCO films the accommodation field B* is considerably enhanced and the critical current density is improved in high fields in the films doped with BaZrO3, e.g. for c = 3.9 wt% by factor of 4.5 in a field of 5 T at 5 K. In the doped films the BaZrO3 particles grow epiaxially with YBCO. Transmission electron microscopy results show that the density of the BaZrO3 particles increases with increasing doping but the particle size remains practically the same (5–10 nm).

The Hall effect in the II–V group semiconductor n-CdSb doped with In is investigated in pulsed magnetic fields up to B = 25 T and temperatures between T = 2 and 77 K for samples oriented along the [0 1 0] and [0 0 1] crystallographic axes. The Hall coefficient, R (B, T), exhibits a sequence of an almost flat region followed by a descending interval and an upturn when B is increased. The decrease of R (B, T) is interpreted by the presence of two groups of electrons with concentrations n2(T) > n1(T) and mobilities μ2(T) < μ1(T). Analysis of n1(T) and n2(T) demonstrates that the high-mobility carriers n1 are the conduction band (CB) electrons, whereas the low-mobility carriers n2 are itinerant electrons of a lower resonant impurity band (IB), having at low T energies of Ei ~ 3–4 meV above the CB edge. In addition, near the CB edge lies a higher IB containing only localized electron states. The IBs are split by spin to states differing by an energy ΔEi ≈ 0.9 meV. The upturn of R (B, T) in the high-field region is explained by the redistribution of the electrons between the IBs due to the decrease of ΔEi when B is increased. The mobility of the CB electrons is determined presumably by strong anisotropic scattering on neutral impurity centres, accompanied at high T by isotropic scattering on acoustic phonons, whereas scattering from ionized impurities is small.

Magnetic properties of the group II–V semiconductor CdSb single crystals doped with Ni (2 at%) are investigated. Deviation of the zero-field-cooled susceptibility, χ ZFC , from the field-cooled susceptibility is observed below 300 K, along with a broad maximum of χ ZFC ( T ) at T b in fields below the anisotropy field B K ∼4 kG. T b ( B ) obeys the law [ T b ( B )/ T b (0)] 1/2 =1– B / B K with T b (0)∼100 K. The magnetization exhibits saturation above ∼20–30 kG, a weak temperature dependence and anisotropy of the saturation value M s . The coercive field is much smaller then B K and displays anisotropy inverted with respect to that of M s . Such magnetic behavior is expected for spheroidal Ni-rich Ni 1− x Sb x nanoparticles with high aspect ratio, broad distribution of the sizes and with orientations of the major axis distributed around a preferred direction.

The Hall coefficient, electrical conductivity and electron mobility are investigated in Ag-doped n-ZnSe single crystals at temperatures between 8 and 500 K immediately after doping the samples and after storing them for 5 years under normal room conditions in darkness. The formation of donor-type Agi interstitial defects stimulated by time is found for the first time. After 5 years storage, the samples show a dramatic increase in the electrical conductivity, free electron concentration and concentration of shallow donors. A model that explains these changes by the displacement of Ag ions into interstitial sites due to lattice deformation forces is proposed. The formation of an Ag-donor impurity band in n-ZnSe:Zn:Ag crystals stored at room temperature is also studied.

Magnetic susceptibility, M-H plot, magnetoresistance and thermoelectric power of the RuSr2Eu1.5Ce0.5Cu2O10 superconductor are measured. Values of the magnetic transition temperature Tmag, superconductivity transition temperature Tc, upper critical field Hc2, chemical potential mu, and energy width for electric conduction W(sigma) are obtained from these measurements. It has been found that Tmag = 140 K, Tc = 25 K (33 K) from susceptibility (magnetoresistance) measurements, Hc2 (0) > 32 T, mu = 8 meV, and W(sigma) = 58.5 meV. These values are compared with other ruthenate superconductors, and resulting physical information is discussed., 18 pages of TEXT + FIGS. To appear in - J. PHYS. COND. MATT. (2006)

The magnetic properties of oriented CdSb single crystals doped with 2 at% of Ni are investigated. From measurements of magnetic irreversibility defined by deviation of the zero-field-cooled (ZFC) susceptibility from the field-cooled (FC) susceptibility, the value of the mean anisotropy field BK ~ 4 kG is obtained. The ZFC susceptibility displays a broad maximum at a blocking temperature, Tb, depending on B according to the law [Tb(B)/Tb(0)]1/2 = 1 ? B/BK with Tb(0) ~ 100 K. The field dependence of the magnetization exhibits saturation above ~20?30 kG with values of Ms different for B along the [1?0?0], [0?1?0] and [0?0?1] axes. The temperature dependence of Ms is weak, increasing slightly upon cooling the sample below ~100 K. The temperature dependence of the coercive field, Bc(T), is weak above Tb but is enhanced strongly with decreasing temperature below Tb. The anisotropy of Bc is inverted with respect to the anisotropy of Ms. Such behaviour can be attributed to spheroidal Ni-rich Ni1?xSbx nanoparticles with a high aspect ratio, broad size distribution and distribution of the orientation of the major axis around a preferred direction. The relation Bc BK and the anisotropies of Ms and Bc are consistent with reversal of the magnetization by the curling mode, whereas the Tb(B) dependence is typical of the coherent rotation mode. This difference is connected to the proximity of the average transversal cluster radius to a critical value for transition between the two magnetization reversal modes within a wide crossover interval, due to broad distribution of the cluster sizes.

Magnetic susceptibility, χ ( T ) , is investigated in ceramic La 1− x Ba x MnO 3 (LBMO) with x = 0.02 – 0.25 in the range of fields B = 10 – 80 G and temperatures T = 5 – 310 K . All samples exhibit a paramagnetic (PM) to ferromagnetic (FM) transition with T C increasing with x from 177 K ( x = 0.02 ) to 295 K ( x = 0.25 ) and magnetic irreversibility decreasing below T C with increasing x . In the PM phase an interval of the Curie–Weiss behavior of χ ( T ) with an effective Bohr magneton number, p eff ∼ 30 – 40 , is observed above T 1 ∼ 260 – 290 K . Below T 1 and down to T cr ∼ 190 – 220 K the susceptibility follows the scaling law χ - 1 ( T ) - χ - 1 ( T C ) ∼ ( T / T C - 1 ) γ with γ = γ 1 ≈ 1.4 corresponding to a three-dimensional (3D) Heisenberg spin system. Below T cr , χ ( T ) obeys the same scaling law as for T > T cr , but with another value of γ = γ 2 ≈ 1.7 – 1.8 , characteristic of a 3D percolation system. The temperature dependence of the susceptibility observed in the PM phase is explained by small FM particles embedded in the host LBMO matrix above T 1 . The size of these particles increases between T 1 and T cr up to nanometer scale, forming critical percolation clusters below T cr . The magnetic irreversibility is connected to a mixed, FM and cluster-glass, phase.