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In this work, we investigated the critical currents and pinning mechanisms in single crystals of the high-temperature superconductor Y123 with Mo substituted into CuO chains. The single crystals were annealed in oxygen at low (130–140 atm) and high (255 atm) pressure, which significantly influenced the observed properties. Magnetic hysteresis loops were measured at various temperatures in fields up to 14 T, for both H||c and H⊥c. On the basis of these measurements, the densities of critical currents were calculated using the Bean critical state model. Then, using the Kramer approach and the Dew-Hughes model, scaling of the pinning force was performed and the type of pinning centers and pinning mechanisms dominant in different field and temperature ranges were determined. Due to Mo substitution, the critical current density in single crystals annealed in oxygen under high pressure increased several times at lower temperatures, e.g., 3–4 times for T = 4–35 K and μ 0 H = 1–8 T, and by an order of magnitude at higher temperatures, e.g., for T = 65–75 K and μ 0 H = 2–3 T. For these single crystals, Δκ volume-like pinning centers (Mo2O11 octahedra dimers) and normal point-like pinning centers (interstitial oxygen) were identified as dominant at lower and higher fields, respectively. [ABSTRACT FROM AUTHOR]

Magnetic measurements have been performed under pressure of 0-9.7 kbar and in the temperature range of 5-300K for the hole-doped Nd1-xCaxBaCo2O5.5 system over the composition range x=0-0.06, where a strong competition between antiferromagnetic and ferrimagnetic phases is present. The dependence of TN, i.e., of the temperature of a first order phase transition from the antiferromagnetic to the ferrimagnetic state, and of TC, i.e., of the temperature of the second order phase transition from the ferrimagnetic to the paramagnetic state on hydrostatic pressure was found to be a function of hole doping. The large pressure-induced increase of TN becomes enhanced with increasing of the hole doping level, while a small pressure-induced increase of TC is suppressed by increasing the hole doping level. This finding shows that the hydrostatic pressure stabilizes the antiferromagnetic phase, whereas the hole doping alone suppresses the antiferromagnetic phase. All investigated compounds have revealed the existence of a certain fraction of ferrimagnetic phase at temperatures much below TN. An increase of a magnetization observed in high magnetic field of 50 kOe at temperatures much below TN was explained as the high-field induced polarization of Nd3+ magnetic moments, appearing in the magnetic field exceeding the strength of Nd-Co antiferromagnetic exchange interactions. [ABSTRACT FROM AUTHOR]

In this study, the possibility of using four different GO derivatives as nanocarriers for meso-tetraphenylporphyrin (TPP) (GO_TPP) was evaluated. The research was carried out with the innovative, well-reproducing tumor environment of 2D and 3D MCF-7/HMF co-cultures in a single microfluidic Cell-on-a-Chip system. A significant accumulation of TPP in cancer cells for the tested GO_TPP nanoconjugates was achieved. This resulted in a decrease of MCF-7/HMF cell viability cultured as 2D and 3D models. Our research confirmed that the driving force of a decrease of MCF-7/HMF cell viability after PDT procedures with GO_TPP was associated with the efficient generation of reactive oxygen species (ROS). It was proved that the tested conjugates did not show any cytotoxic effect on MCF-7/HMF co-cultures without irradiation. Therefore, the herein presented nanoconjugates can be treated as non-toxic materials for humans that after activation can be applied as highly efficient probes for PDT. [ABSTRACT FROM AUTHOR]

Electrical conductivity, magnetic susceptibility, and point contact Andreev reflection (PCAR) studies were done on bulk, polycrystalline SrRu1-x(TM)xO3 (TM=Cr, Mn, Ti) and SrRu0.92O3 with a high degree of disorder. Fits of the temperature dependence of the latter using the Curie–Weiss law yielded values for the Curie–Weiss temperature, Θ. Furthermore, the values of the Curie temperature, TC were identified by determining the maximum susceptibility as a function of temperature. PCAR measurements were done to determine the transport spin polarization, Pt (0≤Pt≤1.0). Pure SrRuO3 undergoes ferromagnetic ordering at a Curie temperature of TC∼160 K and has a relatively high spin polarization (∼0.6). Our results indicate that when the lattice is disordered from either the presence of Ru lattice site defects or the substitution of a transition metal for the Ru, TC changes by a factor of 2, and Θ by a factor of 1.7. By contrast, the spin polarization is unchanged for both SrRu0.94Ti0.06O3 and SrRu0.9Mn0.1O3, while it is barely changed (P=0.5) for SrRu0.9Cr0.1O3. [ABSTRACT FROM AUTHOR]

SrRuO3 (SRO) thin films were grown on SrTiO3 (100) substrates using the pulsed laser deposition method. In order to fully exploit the correlation between their properties and the partial (working) pressures of oxygen in which they are grown, a wide range of pressures-from 0.1 to 300 mTorr-was investigated. SRO ablation plumes showed a shape transition from forward directed to confined isotropic at 60 mTorr. Also, all measured properties of SRO films displayed significant changes at 60 mTorr. Out-of-plane lattice constants and strains of SRO films were quite large for low-pressure growth (up to 10 mTorr), but became notably minimized at 60 mTorr and continued to change gradually with further pressure increases. Ru deficiencies seemed to occur regardless of working pressure value. The island growth mode was dominant for low pressures up to 10 mTorr, followed by the step flow growth mode at 60 mTorr and step flow plus two-dimensional growth at 200 mTorr, reverting then back into island growth at 300 mTorr. Only those SRO films exhibiting the step flow growth mode showed a high TC. The correlation between oxygen pressure and film properties is discussed in terms of strain and compositional effects. [ABSTRACT FROM AUTHOR]

Structural and magnetic properties have been studied for polycrystalline Zn[sub 1-x]TM[sub x]O, where TM (transition metal ions)=Mn, Fe, and Co. No bulk ferromagnetism was observed for single-phase materials, contrary to the existing theories. Single-phase samples demonstrate paramagnetic Curie–Weiss behavior with antiferromagnetic interactions, similar to other diluted magnetic semiconductors. Nonoptimal synthesis conditions lead to formation of second phases that are responsible for spin-glass behavior {ZnMnO[sub 3] impurity for Zn[sub 1-x]Mn[sub x]O [S. Kolesnik et al., J. Supercond. 15, 251 (2002)]} or high-temperature ferromagnetic ordering [Co metal for Zn[sub 1-x]Co[sub x]O with the Curie temperature T[sub C]>800 K or (Zn,Fe)[sub 3]O[sub 4] for Zn[sub 1-x]Fe[sub x]O with T[sub C]=440 K]. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetocaloric effect and specific heat of a La[sub 0.845]Sr[sub 0.155]MnO[sub 3] sample were measured over a temperature range of 4.2-300 K, to verify whether large entropy changes induced by magnetic field make possible the use of manganites for magnetic refrigeration and whether a magnetostrictive contribution to magnetocaloric effect is significant. Isothermal entropy change and adiabatic temperature change induced by ΔB = 7 T were determined as functions of temperature. Near to the Curie temperature, T[sub c]≈234 K, they reach, respectively, ∼ -6.6 J/(kg K) and ∼3.4 K, i.e., the values ∼2 and ∼4 times smaller than for Gd. Despite the presence of large magnetostriction, its contribution to magnetocaloric effect was found negligible. [ABSTRACT FROM AUTHOR]

We have studied magnetoresistance of a series of La[sub 1-x-y]Ca[sub x]Sr[sub y]MnO[sub 3+d] samples with the Curie temperature (T[sub C]) close to room temperature. For these samples, the rhombohedral-orthorombic structural phase transformation temperature (T[sub s]) is slightly higher than T[sub C]. On cooling in zero magnetic field, we observe a rapid increase of resistivity at T[sub s]. This increase is followed by a rapid decrease due to the ferromagnetic transition. The applied magnetic field significantly shifts the ferromagnetic transition to higher temperatures and suppresses the structure-related resistivity increase. We show that a combination of these two effects leads to an enhancement of the negative magnetoresistance due to strong spin-lattice coupling. Furthermore, by annealing the samples at appropriate temperatures in air, the enhancement can be optimized to appear in relatively low magnetic fields and at room temperature. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on a study on the magnetostriction measurements for stoichiometric La...-...Sr...MnO... samples with x=0.11, 0.13, and 0.165 in magnetic fields to 12 T. Sample preparation and experimental details; Magnetic and resistive properties; Magnetostrictive properties; Conclusion.

The electronic structures of SrMn1-xRuxO3 (0⩽x⩽1) have been investigated by employing soft x-ray absorption spectroscopy (XAS). The measured Mn 2p XAS spectra for SrMn1-xRuxO3 show that the valence states of Mn ions change monotonically from Mn4+ for x=0 to ∼Mn3+ for x=0.8, suggesting that the valence states of the substituted Ru ions are higher than 4+. The Ru 3p XAS spectra of SrMn1-xRuxO3 show the existence of pentavalent Ru5+ ions for the low x value. The measured O 1s XAS spectra also support these findings. [ABSTRACT FROM AUTHOR]

The temperature-dependent electronic structure of ferromagnetic double perovskite La2MnNiO6 has been investigated by employing soft x-ray magnetic circular dichroism (XMCD) and soft x-ray absorption spectroscopy (XAS). The measured 2p XAS spectra for Mn and Ni ions at low temperature show that most of Mn ions are formally tetravalent (3d3) and that Ni ions are divalent (3d8). The measured Ni 2p core-level x-ray photoemission spectroscopy spectrum also supports the divalent states of Ni ions. With increasing temperature, the measured XMCD intensity decreases, in agreement with its high Curie temperature. The line shapes of both XMCD and XAS spectra do not change with temperature, suggesting that the valence states of La2MnNiO6 do not change with temperature. [ABSTRACT FROM AUTHOR]

The electronic structure of ferromagnetic double-perovskite La2MnNiO6 has been investigated by employing Mn and Ni 2p→3d resonant photoemission spectroscopy (RPES) and soft x-ray absorption spectroscopy (XAS). The Mn and Ni 2p XAS measurements show that Mn ions are formally tetravalent (3d3) and that Ni ions are formally divalent (3d8). Mn and Ni 2p→3d RPES shows that the occupied Mn 3d3 (t2g3↑) states are sharp and located around 2 eV below EF, while the occupied Ni 3d8 (t2g3↑t2g3↓eg2↑) states are broader than the Mn 3d states and they extend from EF to ∼5 eV below EF. [ABSTRACT FROM AUTHOR]

The electronic structures of SrMn1-xFexO3 (0≤x≤1) have been investigated by using photoemission spectroscopy (PES) and soft x-ray absorption spectroscopy (XAS). Mn ions in SrMnO3 are found to be in the nearly tetravalent (Mn4+) states, but with a small mixture of the Mn2+ configuration. With increasing x in SrMn1-xFexO3, Mn ions remain in the 4+ states. Fe ions in SrMn1-xFexO3 are also in the nearly tetravalent (Fe4+) states for the whole range of x. Valence-band PES reveals that the occupied Mn t2g3 states are located about 2.5 eV below EF, while the occupied Fe t2g3eg1 states are broader than the Mn 3d occupied states, and are located between 3 and 6 eV below EF. The large overlap between Fe 3d and the O 2p states is found in SrFeO3, reflecting the strong hybridization between the Fe 3d states and the O 2p states, in agreement with the metallic nature of SrFeO3. [ABSTRACT FROM AUTHOR]

Context. Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20–90 MHz) is now possible with the Low Frequency Array (LOFAR), opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. Aims. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon. Methods. Thetype II shock source-positions and spectra were obtained using 91 simultaneous tied-array beams of LOFAR, and the CME was observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and by the COR2A coronagraph of the SECCHI instruments on board the Solar Terrestrial Relation Observatory(STEREO). The 3D structure was inferred using triangulation of the coronographic observations. Coronal magnetic fields were obtained from a 3D magnetohydrodynamics (MHD) polytropic model using the photospheric fields measured by the Heliospheric Imager (HMI) on board the Solar Dynamic Observatory (SDO) as lower boundary. Results. The type II radio source of the coronal shock observed between 50 and 70 MHz was found to be located at the expanding flank of the CME, where the shock geometry is quasi-perpendicular with θBn ~ 70°. The type II radio burst showed first and second harmonic emission; the second harmonic source was cospatial with the first harmonic source to within the observational uncertainty. This suggests that radio wave propagation does not alter the apparent location of the harmonic source. The sources of the two split bands were also found to be cospatial within the observational uncertainty, in agreement with the interpretation that split bands are simultaneous radio emission from upstream and downstream of the shock front. The fast magnetosonic Mach number derived from this interpretation was found to lie in the range 1.3–1.5. The fast magnetosonic Mach numbers derived from modelling the CME and the coronal magnetic field around the type II source were found to lie in the range 1.4–1.6. [ABSTRACT FROM AUTHOR]

Magnetic anisotropy of pure and substituted laser-ablated SrRuO3 and SrRu0.9Cr0.1O3 thin films has been studied by rotational magnetization experiments in a superconducting quantum interference device (SQUID) magnetometer. The magnetic easy axis for epitaxial (single domain) SrRuO3 and SrRu0.92O3 thin films lies in the (001) plane and is tilted away from the normal to the surface by 23°-26°. Its direction lies between the [110] and [010] axes. For the lower oxygen pressure grown SrRuO3 thin film, which consists of intertwined crystal nanodomains the magnetic easy axis is no longer locked-in to the (001) plane but is oriented closer to the normal to the surface that is the resultant orientation of easy axes for different domains. Similar effect is observed in single-domain SrRu0.9Cr0.1O3 thin film with random Cr substitution on the RuO6 octahedra. A role of ruthenium deficiency observed in all the studied thin films is also discussed. [ABSTRACT FROM AUTHOR]

The nearest-neighbor magnetic exchange interactions in Zn0.95Mn0.05O, Zn0.95Co0.05O, and Zn0.98Mn0.02Te were investigated by measuring inelastic neutron scattering from isolated exchange-coupled spin-spin pairs. The experiments on Zn0.98Mn0.02Te were carried out at atmospheric pressure and then at 4 kbar pressure in order to determine the dependence of the exchange parameter on the spin-spin distance. [ABSTRACT FROM AUTHOR]

Point-contact Andreev reflection (PCAR) measurements were made on bulk polycrystalline SrRu0.8Ti0.2O3 and SrRu0.92O3 samples to determine the transport spin polarization. The parent compound SrRuO3 undergoes ferromagnetic ordering at TC~160 K with relatively high spin polarization (~60%). For the SrRu0.8Ti0.2O3 and SrRu0.92O3 samples, a reduction in TC occurs. Moreover, our measurements indicate that the SrRu0.8Ti0.2O3 system retains a high degree of spin polarization (P~0.6), similar to the parent compound. However, due to the insulating nature of SrRu0.92O3, the PCAR technique did not yield information on P. Instead, the data displayed nonlinear I-V consistent with the tunnelinglike spectra. [ABSTRACT FROM AUTHOR]

Structural and magnetic properties have been studied for polycrystalline Zn1-xMnxO (x=0.02,0.03,0.05). Low-temperature (∼500 °C) synthesis leaves unreacted starting ZnO and manganese oxides. Contrary to a recent report, no bulk ferromagnetism was observed for single-phase materials synthesized in air at temperatures above 900 °C. Single-phase samples show paramagnetic Curie–Weiss behavior. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The temperature of the superconducting transition of RU[sub 1-x]Sr[sub 2]RECu[sub 2+x]O[sub 8-d] (RE=Gd, Eu) compounds was raised up to 72 K (for x = 0.4; compare to Tc= 45 K observed for RuSr[sub 2]GdCu[sub 2]O[sub 8]) by changing the ratio between Ru and Cu. Magnetization experiments performed under external pressure for RE=Gd: x=0.1, 0.2, 0.3, and 0.4, and RE=Eu: x=0.4 samples reveal that T[sub c] increases at a rate of 5-6 K/GPa. The hole doping achieved along the series has been probed in Hall effect, thermopower, and XANES experiments and is found to increase with x. Muon spin rotation spectroscopy experiments reveal the presence of a low temperature magnetic transition for Ru[sub 0.6]Sr[sub 2]EuCu[sub 2.4]O[sub 8-d] (T[sub m] ≈ 5 K), similar to that recently observed in the RU[sub 1-x]Sr[sub 2]GdCu[sub 2+x]O[sub 8-d] system [P. W. Klamut, et al., Physica C 364, 313 (2001)]. Low temperature magnetization data suggest the constrained dimensionality of the superconducting phase in both RE=Gd and Eu based compounds. [ABSTRACT FROM AUTHOR]

We present magnetization and resistivity data on polycrystalline samples of Pr[sub 1-x]Sr[sub x]MnO[sub 3] (0.58≤x≤1.00). All the samples are antiferromagnetic insulators at low temperatures. For 0.78

The effect of oxygen stoichiometry on properties of La[sub 0.815]Sr[sub 0.185]MnO[sub 3+d] was studied for samples with oxygen content controlled by quenching from high temperatures (700–1400 °C) in air, cooling under low oxygen partial pressure, and annealing at high oxygen pressure. The oxygen content determined from thermogravimetric analysis was found to vary within a range of 3.00–3.10. At room temperature the lattice parameters of the rhombohedral structure (R3¯c) decrease linearly with increasing oxygen content. The rhombohedral-orthorhombic structural transition temperature decreases abruptly with increasing oxygen content while the Curie temperature increases with increasing oxygen content, reaching a maximum at d∼0.04, and then decreases. The saturation magnetization decreases linearly with increasing oxygen content indicating increasing Mn[sup 4+] concentration, i.e., hole doping by cation vacancies. Finally the magnetoresistance effect decreases with increasing d. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Muon spin rotation experiments performed on a series of La[sub 2-x]Ca[sub 1+x]Cu[sub 2]O[sub 6] (x=0.12, 0.16, 0.22) superconductors indicate the existence of the magnetic correlations in the superconducting phase below T∼6 K. The increase in sample inhomogeneity strengthens these correlations. For the superconducting phase, the extrapolated σ(0) values fulfill the universal Uemura relation between T[sub c] and σ(0). © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents the study that determined the f-electron excitation spectra of neodymium ions in superconducting neodymium barium[sub2]copper[sub3]oxygen[sub7] and semiconducting neodymium[sub2.5]barium[sub1.5]copper[sub3]oxygen[sub7] by inelastic neutron scattering. Experimental details; Results and discussion.

The normal state in the hole underdoped copper oxide superconductors has proven to be a source of mystery for decades. The measurement of a small Fermi surface by quantum oscillations on suppression of superconductivity by high applied magnetic fields, together with complementary spectroscopic measurements in the hole underdoped copper oxide superconductors, point to a nodal electron pocket from charge order in YBa2Cu3O6+δ. Here, we report quantum oscillation measurements in the closely related stoichiometric material YBa2Cu4O8, which reveals similar Fermi surface properties to YBa2Cu3O6+δ, despite the nonobservation of charge order signatures in the same spectroscopic techniques, such as X-ray diffraction, that revealed signatures of charge order in YBa2Cu3O6+δ. Fermi surface reconstruction in YBa2Cu4O8 is suggested to occur from magnetic field enhancement of charge order that is rendered fragile in zero magnetic fields because of its potential unconventional nature and/or its occurrence as a subsidiary to more robust underlying electronic correlations. [ABSTRACT FROM AUTHOR]

The crystal structure of PrInO3 was investigated in the temperature range 303–1123 K by high-resolution neutron-powder diffraction. The PrInO3 adopts a highly distorted variant of the perovskite structure with the orthorhombic Pnma space group in the whole temperature range investigated. The bond length and bond-angle analysis revealed a very slow tendency to decrease structural distortion with increasing temperature. Comparison of different parameters quantifying perovskite structure distortion calculated for PrInO3 and the similar PrAlO3 and PrGaO3 shows the advantage of using the tolerance factor t12 calculated for the 12-fold coordinated Pr by geometrical averaging of the individual interatomic distances. An additional advantage of the tolerance factor method results from the possibility of extending it to predict the average structural distortion and the geometrical stability of the perovskites at various temperatures once the accurate dependence of t(x,T,d) on the composition, temperature and oxygen content is found. By comparing PrInO3 with several AMO3 perovskites containing ions in the fixed oxidation state on the A and M crystal sites it was found that structural distortion and the tolerance factor t12 for PrInO3 are consistent with the empirical thermal expansion coefficient based on the bond strength calculation [R. M. Hazen, and C. T. Prewitt, Am. Mineral., 1977, 62(3–4), 309]. In contrast to perovskites AMO3-d containing mixed-valent M ions, which allow for a wide range of changes of the tolerance factor t12(T,d) as a function of oxygen content, perovskites AMO3 with M ions in the fixed oxidation state show much less flexibility. This flexibility is further reduced for the A3+M3+O3 perovskites like PrInO3 for which even a large change of the synthesis temperature has a minor effect on controlling the resulting t12(T) and the structural phase in comparison with A2+M4+O3 perovskites. The only parameter left for A3+M3+O3 materials allowing formation of various perovskites and hexagonal phases is the total pressure, which may significantly change t12(T,P). [ABSTRACT FROM AUTHOR]

Numerous solar radio bursts were observed in 2000 - 2001 using the Toruń radio spectrograph with its unique time resolution of 80 microseconds. This high time resolution enables an in-depth analysis of the time evolution of the power spectra and Fourier spectral indices of selected short radio bursts. We analyze the power-spectrum parameters and variability for two millisecond radio dm-spike events and one drifting pulsation structure (DPS) event, for which the structures of the recorded signals were analyzed with an effective time resolution of 0.0008 s in five adjacent frequency bands of their radio spectra. We found that Fourier spectral indices varied rapidly when radio fine structures were recorded. Otherwise they remained close to zero, indicating the presence of noise. For the 10 - 40 Hz frequency interval of the power spectra the mean values of the Fourier spectral indices varied up to −1.51 for the dm-spikes and up to −1.53 for the DPS event. Cross-correlation coefficients of radio fluxes in adjacent frequency bands varied between 0.12 and 0.60 for dm-spikes and between 0.77 and 0.94 for the DPS event. The shortest fine structure found in the studied events lasted 0.001 s. These results are entirely new for dm-radio spikes and confirm a single previous result found for the DPS events. On the basis of our results, we propose that dm-spikes and DPS events are physically similar and that both are signatures of cascades of interacting plasmoids of different sizes. [ABSTRACT FROM AUTHOR]

Fe-doping (up to 11 mole%) into SrRuO (SRO) thin films on SrTiO substrates decreased correlation lengths of both surface and interface. It turned out that Fe was doped in the valence state of 3+ without formation of the FeO phase, which caused orthorhombic distortion. T values decreased from 145 K to 97 K with increasing Fe concentration ( C). High magnetic switching fields were observed for all Fe-doped SRO thin films and their strengths showed a linear relationship with C. Detail structural characterization using synchrotron X-ray diffraction and X-ray photoemission spectroscopy were used to understand its unique magnetic switching field properties. [ABSTRACT FROM AUTHOR]

We present the results of the analysis of thirteen events consisting of dm-spikes observed in Toruń between 15 March 2000 and 30 October 2001. The events were obtained with a very high time resolution (80 microseconds) radio spectrograph in the 1352 - 1490 MHz range. These data were complemented with observations from the radio spectrograph at Ondřejov in the 0.8 - 2.0 GHz band. We evaluated the basic characteristics of the individual spikes (duration, spectral width, and frequency drifts), as well as their groups and chains, the location of their emission sources, and the temporal correlations of the emissions with various phases of the associated solar flares. We found that the mean duration and spectral width of the radio spikes are equal to 0.036 s and 9.96 MHz, respectively. Distributions of the duration and spectral widths of the spikes have positive skewness for all investigated events. Each spike shows positive or negative frequency drift. The mean negative and positive drifts of the investigated spikes are equal to −776 MHz s and 1608 MHz s, respectively. The emission sources of the dm-spikes are located mainly at disk center. We have noticed two kinds of chains, with and without frequency drifts. The mean durations of the chains vary between 0.067 s and 0.509 s, while their spectral widths vary between 7.2 MHz and 17.25 MHz. The mean duration of an individual spike observed in a chain was equal to 0.03 s. While we found some agreement between the global characteristics of the groups of spikes recorded with the two instruments located in Toruń and Ondřejov, we did not find any one-to-one relation between individual spikes. [ABSTRACT FROM AUTHOR]

The Atacama Large Millimeter/sub-millimeter Array (ALMA) is a large interferometer that will consist up to 64 high-precision antennas operating in the 31.3 - 950 GHz frequency range. In this frequency range, which is largely unexplored, unique observations with a broad range of scientific objectives (cosmology, cold universe, galaxies, stars and their formation, planets and so on) are expected. Among these tasks there is a unique possibility to observe the Sun and to address several outstanding issues of solar physics. First, the ALMA is briefly described and then the new ESO-ALMA European node (ARC), built at Ondřejov Observatory, is presented. In Europe, this ARC is the only one oriented to solar physics. Consequently, the requirements and limitations for ALMA solar observations, as well as some examples of possible solar-oriented ALMA projects, are shown. A procedure of the preparation and submission of proposals for ALMA observations is mentioned. [ABSTRACT FROM AUTHOR]

Alternating current susceptibility and direct current magnetization have been studied for polycrystalline Ca1− xMn xO. On increasing the Mn content, magnetic ordering changes from spin glass behavior for 0.25 ≤ x ≤ 0.4 to antiferromagnetic order. The paramagnetic/antiferromagnetic transition is of second order for 0.5 ≤ x ≤ 0.65 and of first order for x ≥ 0.7. For low Mn concentrations, the high-temperature alternating current susceptibility can be described by a diluted Heisenberg magnet model developed for diluted magnetic semiconductors. [ABSTRACT FROM AUTHOR]

We describe results of several macroscopic and local measurements of magnetic and superconducting properties for pure and Ce and Cu substituted RuSr2GdCu2O8. From various experiments the physical properties phase diagram is derived as a function of the hole doping. We show that the large contribution of polarized Gd3+ magnetic moments to magnetization causes apparent absence of the Meissner state and augments the weak Ru ferromagnetism. This weak ferromagnetism in the superconducting state can be significantly enhanced by the external magnetic field. These results indicate that the low-temperature behavior can be qualitatively explained assuming a quasi-two-dimensional character of the superconducting regions. [ABSTRACT FROM AUTHOR]

Alternating current susceptibility has been studied for polycrystalline Zn1 − xMn xO. Stoichiometric samples demonstrate Curie–Weiss behavior, which indicates mostly antiferromagnetic interactions. Magnetic susceptibility can be described by a diluted Heisenberg magnet model developed for semimagnetic semiconductors. High-pressure oxygen annealing induces spin-glass like behavior in Zn1 − xMn xO by precipitation of ZnMnO3 in the paramagnetic matrix. [ABSTRACT FROM AUTHOR]

We have realized planar tunnel junctions using both Y123 and Y124 single crystals as base electrodes and Pb as counterelectrode. The crystals, with T =90 K (Y123) and T =80 K (Y124), have been chemically etched and natural barriers were formed by a short air exposure. We have compared the tunneling spectra obtained on both systems. The features at about±18mV of the Y123 compound are still observed in the Y124, while the low-bias structures at ±5 mV are not present in the tunneling characteristics of the Y124 system. Linearity of the background conductance is also observed, with less steep slopes in Y124 that might indicate a reduced interlayer coupling in this system. [ABSTRACT FROM AUTHOR]