Diamagnetic Signal Research Articles

New Pb-based Superconductor with the 1222 Structure in the (Pb0.75P0.25)Sr2(Eu1.9−x Ce x Sr0.1)Cu2O z System

New Pb-based 1222 cuprates containing phosphorus have been synthesized in the (Pb,P)Sr2(Eu,Ce,Sr)2 Cu2Oz system. From X-ray powder diffraction study, almost the single 1222 phase samples are found to be obtained in a considerable wide composition area of 0.3≤x≤1.2 for the nominal composition of (Pb0.75P0.25)Sr2(Eu1.9−xCexSr0.1) Cu2Oz. The crystal structure for each sample has a tetragonal symmetry and the typical lattice parameters are a=0.3851 nm and c=2.922 nm. After annealing under 143 atm O2 atmosphere at 400 °C, a sample with x=0.3 among the almost-single phase samples shows an onset of resistivity-drop at the highest temperature of about 22 K and zero-resistivity at the highest temperature of about 12 K, then this sample also shows an onset of diamagnetic signal at about 20 K. These phenomena are found to originate from superconductivity of the new 1222 phase.

New Pb-based 1212 Cuprate Superconductors Containing Sulfur, (Pb0.75S0.25)Sr2 (Y1−x Ca x )Cu2O z

New Pb-based 1212 layered cuprates containing sulfur have been synthesized in the (Pb0.75S0.25) Sr2 (Y1−xCax) Cu2Oz system. X-ray diffraction analysis shows that the almost single-phase samples are obtained within a region of 0.0≤x≤0.5. The crystal structure of each sample has a tetragonal symmetry with the typical lattice constants a=0.3837 nm and c=1.186 nm. As Ca content x is increasing, the semiconductor-like behavior is suppressed. But after only annealing under ambient O2 pressure, none of the samples show any trace of superconductivity. On the other hand, when the samples are annealed under high O2 pressure of about 13.6 MPa, they show resistivity dropping phenomenon in a region of 0.5≤x≤0.7. Among them, the lowest resistivity sample with x=0.6 has an onset temperature of the resistivity dropping at about 22.5 K. Moreover, this sample shows a diamagnetic signal at about 21.5 K. These phenomena are attributed to superconductivity.

Non-centro-symmetric superconductorsLi2Pd3B andLi2(Pd0.8Pt0.2)3B: amplitude and phase fluctuation analysis of the experimental magnetizationdata

We report on magnetization data obtained as a function of temperature and magnetic field inLi2(Pd0.8Pt0.2)3B andLi2Pd3B non-centro-symmetric superconductors. Reversible magnetization curves were plotted asM1/2 versusT. This allows study of the asymptotic behavior of the averaged orderparameter amplitude (gap) near the superconducting transition. Results ofthe analysis show, as expected, a mean field superconducting transition forLi2Pd3B. By contrast, a large deviation from the mean field behavior is revealed forLi2(Pd0.8Pt0.2)3B. This is interpreted as due to the strength of the non-s-wave spin-tripletpairing in this Pt-containing compound which produces nodes in the orderparameter and, consequently, phase fluctuations. The diamagnetic signal aboveTc(H) inLi2Pd3B is wellexplained by superconducting Gaussian fluctuations and agrees with the observed mean field transition. ForLi2(Pd0.8Pt0.2)3B the diamagneticsignal above Tc(H) is much higher than the expected Gaussian values and appears to be well explained bythree-dimensional critical fluctuations of the lowest-Landau-level type, which somehowagrees with the scenario of a phase mediated transition.

New Member of the Pb-based 1232 Cuprates Containing Boron, (Pb0.5B0.5)Sr2(RE3−x−y CexSr y )Cu2O z (RE=Ho, Tm, and Y)

We previously reported on discovery of new Pb-based 1232 cuprate containing boron in the (Pb0.5B0.5)Sr2(Er3−x−yCexSry)Cu2Oz system. Recently, a new member of the Pb-based 1232 cuprates containing boron has been synthesized in the (Pb0.5B0.5)Sr2(RE3−x−yCexSry)Cu2Oz systems (RE=Ho, Tm, and Y). In each system, almost the single 1232 phase samples are found to be obtained for the composition area of x=1.7–1.9 and y=0.2, and the sample with x=1.7 is found to show the smallest resistivity. Despite of annealing under 142 atm O2 atmosphere at 400 °C for 4 h, the sample with x=1.7 in each system is a semiconductor with the transport process followed by a three-dimensional variable range hopping conduction. Moreover, it is found that the sample with RE=Ho shows magnetic anomalies at two temperatures of about 11 and 16 K, and the sample with RE=Y shows a diamagnetic signal at about 8 K, respectively.

Magnetic signature of different vegetation species in polluted environment

Detailed magnetic study on vegetation samples from several strongly polluted and clean sites in Bulgaria is carried out in order to evaluate suitability of different species as passive dust collectors in magnetometry. From each location, available species among lichens, mosses, poplar leaves, dandelion, needles have been sampled. Magnetic susceptibility calculated on mass-specific basis shows wide variability between diamagnetic signal up to 846 × 10−8 m3/kg. Lichens and mosses are found to be the species, showing magnetic signals with the strongest contrast between clean and polluted environment. The main magnetic phase is magnetite-like according to the results from thermomagnetic analysis of susceptibility on magnetic extracts. Scanning electron microscopy (SEM) microphotographs reveal the presence of abundant particulate matter on vegetation surface both with anthropogenic (spherules) and lithogenic origin. Magnetic grain size deduced by the ratio of saturation remanent magnetization (SIRM) and mass-specific magnetic susceptibility (χ) and coercivities (Bc and Bcr) suggest that different species accumulate preferentially small SD-like grains from pollution emissions. Contrasting relationship of the ratio of anhysteretic remanent magnetization (ARM) and χ for polluted vs clean sites deduced by needles and lichens may be related to transformation of the accumulated dust particles within lichens’ tissue. This finding indicates that the exact species used as biological dust collector is of importance when studying spatial grain size distribution of magnetic dust particles. Pilot study on polycyclic aromatic hydrocarbons (PAH) content and its relation to magnetic parameters shows good correspondence between high levels of PAHs and high SIRM values for locations affected by non-ferrous industrial production.

Diamagnetic measurements and plasma energy in toroidal systems

The sensitivity of a diamagnetic signal to several operational and geometrical factors is analysed. Among them are the flux conservation in the plasma, eddy currents induced in the outer structures in fast processes, toroidal shift and deformation of the plasma boundary due to its energy change and inhomogeneity of the confining magnetic field. It is shown that in each case, under proper experimental circumstances, the contribution, unaccounted in the traditional theory of diamagnetic measurements, can reach a level compared with β (ratio of the volume-averaged plasma pressure to the magnetic field pressure). The approach is fully analytical with all relevant dependences shown explicitly, allowing easy estimates and suggesting a resolution of the problem in order to restore the accuracy of finding β from diamagnetic measurements. This essentially extends the analysis by Yamaguchi et al (2006 Plasma Phys. Control. Fusion 48 L73) of possible measures to improve the separation of the useful fraction of the measured diamagnetic signal. The approach is aimed at explaining the discrepancies between model estimates and experimental results, unification of a knowledge obtained in separate numerical studies, extending a theoretical basis of magnetic diagnostics and uncovering potential dangers in interpretations. This is also an essential step from traditional cylindrical theory to analytical derivations in the toroidal geometry. The results are equally applicable to tokamaks and stellarators.

New Pb-based 1212 Superconductor Containing Phosphorus, (Pb0.75P0.25)Sr2(Y1−x Ca x )Cu2O z

New Pb-based 1212 compounds containing phosphorus have been discovered in the (Pb1−y P y )Sr2(Y1−x Ca x )Cu2O z system; almost the single 1212 phase samples can be obtained for the composition range of 0.0≤x≤0.6 and y=0.25. The crystal structure for each sample has a tetragonal symmetry with the typical lattice parameters a=0.3828 nm and c=1.182 nm. Among them, the sample with x=0.6 and y=0.25 shows the onset of resistivity drop at about 39 K and zero-resistivity at about 17 K. Moreover, the sample shows a diamagnetic signal at about 38 K. These phenomena are found to originate from superconductivity with the bulk feature.

Formation of a magnetic hole above the mirror-instability threshold in a plasma with sloshing ions

Within the framework of paraxial approximation it is shown that in an anisotropic plasma with sloshing ions confined an open-ended system a magnetic hole is formed near the turning point of the sloshing ions above the threshold of the mirror instability. The magnetic field experiences a jump at the hole boundary from the side of the magnetic mirror. For a small excess over the mirror instability threshold, the surface of the discontinuity has the shape of a truncated paraboloid, and the magnitude of the magnetic field jump at the system axis is proportional to the radius of the hole and gradually decreases to zero away of the axis. It is argued that disappearance of the magnetic hole because of the widening of the sloshing ions angular spread in the course of the neutral beam injection results in abrupt anticorrelated changes of the diamagnetic signals measured near the turning point of the sloshing ions and near the midplane of the gas-dynamic trap.

Inconsistent pressure effect on superconducting transition temperature and volume in Fe1+yTe1−xSex single crystals

The role of Se in determining the superconductivity of Fe1+yTe1−xSex is still unclear. In this paper, we examine the chemical effect generated by Se substitution by applying external pressure on Fe1+yTe1−xSex single crystals. With increasing pressure, the superconducting volume increases; however, the onset temperature of the superconducting diamagnetic signal, Tcmag, does not change monotonically. The inconsistent pressure effect on superconducting volume and Tcmag is in agreement with Se substitution, which suggests that the chemical pressure effect dominates the superconductivity. Our results also imply that the superconducting and magnetic phases coexist in the form of phase separation.

Low temperature synthesis and superconducting properties of polycrystalline T′-(La,Sm)2CuO4

La2−xSmxCuO4+δ with the Nd2CuO4 structure was synthesized by precipitation from fused alkaline hydroxide, CsOH, at 400°C. The as-sintered polycrystalline samples showed no diamagnetic signal, but after post-annealing in vacuum of ≈10−8atm at 650–700°C, the samples with x=0.1 and 0.3 exhibited superconductivity at Tc on=25K. The volume fraction of the superconducting phase estimated from the slope of the Zero-Field-Cooled magnetization data was over 30% for x=0.3, which confirmed that the La1.7Sm0.3CuO4+δ is a bulk superconductor.

Synthesis of New Pb-Based 1232 Cuprate Containing Boron in the (Pb0.5B0.5) Sr2(Er3−x−y Ce x Sr y )Cu2O z System

New Pb-based layered cuprates containing boron with the 1232 structure have been synthesized in the (Pb0.5B0.5)Sr2(Er3−x−yCexSry)Cu2Oz system. Nearly the single 1232 phase samples are obtained for the nominal composition of 1.6≤x≤1.9 and y=0.2. A sample with the composition of (Pb0.5B0.5)Sr2(Er1.2Ce1.6Sr0.2)Cu2Oz shows resistivity-dropping phenomenon below 10 K and it shows a diamagnetic signal at about 9.0 K, though the superconducting volume fraction is very small. From these results, the sample may well be a new Pb-based superconductor with the 1232 structure.

Magnetic properties of gapless semiconductors: PbPdO2 and PbPd0.9Co0.1O2

PbPdO 2 is a new class of gapless semiconductors, which is extremely sensitive to external influences such as temperature, magnetic field, and carrier doping, because of their peculiar band structure. With varying temperature, a broad transition from a high-temperature metallic behavior to a low-temperature insulating behavior was observed at TMI=100 K in the electrical resistivity, which is related to the thermally assisted excitation near the Fermi level due to its gapless band structure. By doping 10% Co for Pd in PbPdO2, the number of hole charge carriers was increased by ten times, and the transition temperature was increased to TMI=150 K. When applying a magnetic field, a ferromagnetic component was found at low temperatures in the magnetization curves of both materials, in addition to diamagnetic background signals for PbPdO2 and paramagnetic background signals for PbPd0.9Co0.1O2. In the low temperature regime, the slope of magnetoresistance is negative, while it is changed into positive with a quadratic form at high temperatures. These results of magnetic properties identify a tendency of strong spin-orbit coupling in the gapless semiconducting compounds.

Anisotropic pressure effects on plasma equilibrium in toroidal systems

General properties of anisotropic plasma equilibrium in tokamaks and stellarators are considered within the approach allowing explicit analytical evaluation of the equilibrium plasma currents and the related integral quantities. This is done to provide a link to the conventional equilibrium theory for isotropic plasma, to find the rules for possible extensions of its results to configurations with anisotropic pressure and to unify the knowledge obtained in separate numerical studies. Expressions for the diamagnetic signal and, mainly, the Pfirsch–Schlüter current in stellarators are considered. Ultimately this leads to a theoretical justification of the method of experimental evaluation of the pressure anisotropy in the Large Helical Device proposed by Yamaguchi et al (2005 Nucl. Fusion 45 L33). The conditions of its applicability are clarified and possible limitations are elucidated. Combined effects of the pressure anisotropy and inward–outward shift of the plasma on the Pfirsch–Schlüter current in stellarators are discussed.

Fluctuation diamagnetism in high-temperature superconductors

The observation of a strong nonlinear diamagnetic signal well above T_c in several cuprate superconductors constitutes clear evidence of the persistence of local superconducting correlations.

Hydrogen effects on crystallinity, photoluminescence, and magnetization of indium tin oxide thin films sputter‐deposited on glass substrate without heat treatment

AbstractIndium tin oxide (ITO) thin films were sputter deposited by using working gas containing hydrogen on glass substrate without any heat treatments. The films demonstrated X‐ray diffraction due to polycrystalline ITO, blue‐green photoluminescence (PL) due to oxygen defects in nano‐structured ITO crystals, and paramagnetic behaviour in temperature dependence of magnetization overlapped with diamagnetic signal from the substrate. The carrier density n of the films was of the order of 1020 cm−3, and varied as an inverse of V‐character with the hydrogen concentration [H] in the gas. The n value peaked at [H] = 1%. Spectral features at ≈430 and ≈470 nm of the PL emission were invariant with [H]. The order of the density of electrons N with spins obeying the Curie law was 1023 cm−3, and the variation in N with [H] was almost parallel to that in n with [H].

Unusual Meissner state of the superconducting ferromagnet UCoGe revealed by differential susceptibility measurements with a polycrystalline sample

UCoGe is a ferromagnet with a Curie temperature TC∼3K at ambient pressure and superconductivity appears within the ferromagnetic phase with a superconducting transition temperature TSC∼0.8K. We have investigated magnetic properties of the ferromagnetic superconductor UCoGe in superconducting states by the differential susceptibility measurements with a polycrystalline sample. We observed unusual diamagnetic signals for magnetic field dependence of the differential susceptibility in superconducting state. We have revealed the sharp peak for the butterfly-shaped hysteresis loop of ferromagnetism observed even in Meissner state and point out the possible coexistence of ferromagnetism and superconductivity inhomogeneously in real space.

Theory of Diamagnetic Signal in Current-Free Stellarators

The toroidal magnetic flux through the plasma column is calculated analytically for current-free stellarators of arbitrary geometry without assumptions on the plasma shape, aspect ratio, etc. This is done with accuracy sufficient for extracting the contribution due to the finite plasma pressure from this flux. The final result is a formula relating the measured diamagnetic signal with β, the ratio of the plasma pressure to the magnetic pressure. This formula is obtained assuming small β and the relative depth of the magnetic well. These are natural conditions for stellarators, therefore the final result can be recommended for magnetic diagnostics without practical limitations.

Superconductivity in Ti-doped iron-arsenide compound Sr4Cr0.8Ti1.2O6Fe2As2

Superconductivity was achieved in Ti-doped iron-arsenide compound Sr4Cr0.8Ti1.2O6Fe2As2 (abbreviated as Cr-FeAs-42622). The X-ray diffraction measurement shows that this material has a layered structure with the space group of P4/nmm, and with the lattice constants a = b = 3.9003 Å and c = 15.8376 Å. Clear diamagnetic signals in ac susceptibility data and zero-resistance in resistivity data were detected at about 6 K, confirming the occurrence of bulk superconductivity. Meanwhile we observed a superconducting transition in the resistive data with the onset transition temperature at 29.2 K, which may be induced by the nonuniform distribution of the Cr/Ti content in the FeAs-42622 phase.

Synthesis of the phenomenology of the underdoped cuprates

The underdoped cuprates have a number of interesting and unusual properties that often seem hard to reconcile with one another. In this paper we show how many of these diverse phenomena can be synthesized into a single coherent theoretical picture. Specifically we present a description where a pseudogap and gapless Fermi arcs exist in the normal state above the superconducting transition temperature ($T_c$), but give way to the observed quantum oscillations and other phenomena at low temperature when the superconductivity is suppressed by a magnetic field. We show the consistency between these phenomena and observations of enhanced Nernst and diamagnetic signals above $T_c$. We also develop a description of the vortex core inside the superconducting state and discuss its relation with the high field phenomena.

Superconductivity in the Pb-based 1222 Cuprate Containing Boron, (Pb0.5B0.5) Sr2(Y1.9−x Ce x Sr0.1)Cu2O z

We previously reported on the discovery of new Pb-based 1222 cuprates containing boron in the (Pb0.5B0.5)Sr2(RE2−x−y Ce x Sr y )Cu2O z (RE = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) systems. However, none of the cuprates was a superconductor, but a semiconductor with the conduction process of a three-dimensional variable range hopping at low temperatures, despite annealing under O2 atmosphere at 100 atm and 400 °C. Recently, we have discovered that some samples showed superconductivity in the (Pb0.5B0.5)Sr2(Y1.9−x Ce x Sr0.1)Cu2O z system. Among them, the sample with x=0.45 shows the highest zero resistivity temperature at about 10 K and it shows a diamagnetic signal starting at abut 16 K with lowering temperature. The superconductivity is considered to originate from the 1222 phase.