Reversible Magnetization Data Research Articles

Study of Nb0.18Re0.82 non-centrosymmetric superconductor in the normal and superconducting states

We examine the evidence for multiband superconductivity and non s-wave pairing in the non-centrosymmetric superconductor (NCS) Nb0.18Re0.82, using electrical transport, magnetization and specific heat measurements. In the normal state, the evolution of electrical resistivity with temperature and magnetic field support the phonon-assisted interband scattering and multiband picture. In the superconducting state, the temperature dependence of the upper critical field, , is found linear and cannot be described within the Werthamer, Helfand and Hohenberg model over the whole temperature range measured. In addition, the observed exceeds the Pauli limit, suggesting non-s-wave pairing. Interestingly, the Kadowaki–Woods ratio and Uemura plot reveal a behavior in Nb0.18Re0.82 which is similar to that found in unconventional superconductors. The normalized superfluid density (ρs), estimated using the temperature dependence of the lower critical field, , is well explained with the help of the multiband description. Phase fluctuation analysis conducted on the reversible magnetization data, reveals a significant deviation from the mean-field conventional s-wave behavior. This trend is interpreted in terms of a non s-wave spin-triplet component in the pairing symmetry as might be anticipated in a NCS where anti-symmetric spin–orbit coupling plays a dominant role. Recently, time reversal symmetry breaking observed in Nb0.18Re0.82 supports this picture.

The effect of low divalent chemical doping on the high field diamagnetic thermodynamic fluctuations of the YBa2Cu3O7-δ single crystals

Abstract We report on reversible dc magnetization data of the YBa2Cu3O7-δ, YBa2Cu2.97Zn0.03O7-δ, YBa2Cu2.97Mg0.03O7-δ and YBa2Cu2.97Ni0.03O7-δ single crystals with the aim of studying the contribution of the divalent chemical doping on the diamagnetic thermodynamic fluctuations (DTF) of the YBa2Cu3O7-δ. The dc zero field cooled [MZFC(T)] and field cooled cooling [MFCC(T)] diamagnetic magnetizations were measured with a SQUID magnetometer. The DTF behavior of our samples was interpreted in light of the 3D lowest Landau level formalism (3D-LLL). The results highlight that the amount of the Cu partially substituted individually for Zn, Mg or Ni in the YBa2Cu3O7-δ structure do not change the 3D character of its vortices dynamics. In addition, they show an increase in the temperature range dominated by 3D-DTF of ours doped single crystals. This increase could be connected to the intensification of their inhomogeneous superconducting state due to the chemical doping.

Effect of fast neutron irradiation induced defects on the metamagnetic transition In Ce(Fe0.96Ru0.04)2

Effect of fast neutron irradiation induced defects on the anti-ferromagnetic (AFM) to ferromagnetic (FM) transition in Ce(Fe0.96Ru0.04)2 is studied by magnetic measurements. We observe that at a given temperature, AFM–FM transition occurs at a lower field in irradiated specimens compared to that in pristine samples. While irradiation does not seem to affect the hysteresis of the transition, zero field susceptibility is enhanced by more than an order of magnitude. Analysis of reversible magnetization vs field data at low fields indicates superparamagnetic behavior of nano-sized FM domains, which are conjectured to nucleate on the crystal defects produced by the fast neutron irradiation. The number density and size of the nano-sized domains in the irradiated and pristine samples are estimated from the magnetization data.

Evidence for Kosterlitz-Thouless and three-dimensionalXYcritical behavior inBi2Sr2CaCu2O8+δ

We present reversible magnetization data of a high-quality ${\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8+\ensuremath{\delta}}$ single crystal and explore the occurrence of three-dimensional (3D)-$xy$ critical behavior close to the bulk-transition temperature ${T}_{c}$ and of Kosterlitz-Thouless (KT) behavior. Below and above the presumed Kosterlitz-Thouless transition temperature ${T}_{\text{KT}}$ we observe the characteristic two-dimensional (2D)-$xy$ behavior: a downward shift in the crossing point phenomenon toward ${T}_{\text{KT}}$ as the field is decreased and sufficiently below ${T}_{\text{KT}}$ the characteristic 2D-$xy$ relationship between the magnetization and the in-plane magnetic penetration depth ${\ensuremath{\lambda}}_{ab}$. In contrast, the measured temperature dependence of the superfluid density does not exhibit the characteristic KT behavior around the presumed ${T}_{\text{KT}}$. The absence of this feature is traced back to the 2D- to 3D-$xy$ crossover setting in around and above ${T}_{\text{KT}}$. Invoking the Maxwell relation, the anomalous field dependence of the specific-heat peak is also traced back to the intermediate 2D-$xy$ behavior. However, close to ${T}_{c}$ we observe consistency with 3D-$xy$ critical behavior in agreement with measurements of ${\ensuremath{\lambda}}_{ab}$.

3D-xy criticalproperties of YBa2Cu4O8 and magnetic-field-induced 3D to 1D crossover

We present reversible magnetization data of aYBa2Cu4O8 single crystal and analyzethe evidence for 3D-xy critical behavior and a magnetic-field-induced 3D to 1D crossover. Remarkable consistencywith these phenomena is observed in agreement with a magnetic-field-inducedfinite size effect, whereupon the correlation length transverse to the appliedmagnetic field cannot grow beyond the limiting magnetic length scaleLH = (Φ0/(aH))1/2. By applying the appropriate scaling form we obtain the zero-field critical temperature,the 3D to 1D crossover, the vortex melting line and the universal ratios of therelated scaling variables. Accordingly there is no continuous phase transition in the(H,T) planealong the Hc2 lines as predicted by the mean-field treatment.

Vanishing of the upper critical field inBi2Sr2CaCu2O8+δfrom Landau-Ott scaling

We apply Landau-Ott scaling to the reversible magnetization data of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ published by Wang et al. [Phys. Rev. Lett. 95, 247002 (2005)] and find that the extrapolation of the Landau-Ott upper critical field line vanishes at a critical temperature parameter ${T}_{c}^{*}$ a few degrees above the zero resistivity critical temperature ${T}_{c}$. Only isothermal curves below and near ${T}_{c}$ were used to determine this transition temperature. This temperature is associated with the disappearance of the mixed state instead of a complete suppression of superconductivity in the sample.

A Study on the Temperature Dependence of the Ginzburg-Landau Parameter, Thermodynamic and Upper Critical Field of ${\rm Nb}_{3}{\rm Sn}$ Strands

We report detailed magnetization measurement results for two internal-tin Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands. The paramagnetic background of a Mitsubishi strand is about 4 times larger than that of a KAT strand below the transition temperature, which can be understood as combined effects of Pauli and Langevin paramagnetism. From magnetic relaxation measurement for the KAT strand, a possibility of surface barrier effect is discussed. After subtracting the paramagnetic background, reversible magnetization data are analysed using the Hao-Clem model and the Ginzburg-Landau parameters (kappa), the thermodynamic and the upper critical fields (B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ,B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</sub> ) at various temperatures are obtained. The temperature dependences of kappa, B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</sub> are compared with the recent theoretical calculation results for Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and also with widely used empirical formulas.

Three-dimensional and two-dimensional high field vortex fluctuations in deoxygenated YBa 2Cu 3O 7− x depending on the vicinity of Tc( H)

We analyzed reversible magnetization data, M versus T curves, of three single crystals of YBa 2Cu 3O 7− x (Y123), with superconducting transition temperatures T c = 62.5 ( x = 0.35), 52 ( x = 0.5), and 41 K ( x = 0.6). M versus T curves of each sample exhibited a field independent crossing point, M( T ∗), occurring close to the superconductor critical temperature. These crossing points were shown to be due to fluctuations of vortices. Besides the reversible data of each sample were shown to obey a two-dimensional diamagnetic lowest-Landau-level (LLL) fluctuation theory, it is shown here that the data, within a temperature region where the crossing points occur for two samples (62.5 K and 52 K), are also explained by a three-dimensional version of this fluctuation theory. Since the crossing points for these two samples occur close to T c, these are interpreted as been due to three-dimensional vortex fluctuations instead two-dimensional ones. An expression for the field independent magnetization, M( T ∗), which is expected to occur at the crossing point of the various M versus T curves, is obtained for the case of three-dimensional vortex fluctuations, and compared to the experimental values of M( T ∗). This comparison produced consistent values for the coherence length along the c-axis of the samples with T c = 62.5 and 52 K, solving an inconsistent result previously published, when experimental values of M( T ∗) were compared with an expression obtained from two-dimensional vortex-fluctuations. The results of the present work show that, despite the fact that two-dimensional LLL fluctuations scaling is obeyed in a much wider temperature range for two studied samples ( T c = 52 ( x = 0.5), and 62.5 K ( x = 0.35)) when compared to the 3D-LLL scaling form, these systems behave as three-dimensional for temperatures close to T c( H).

A Comparative Study of High-Field Diamagnetic Fluctuations in Deoxygenated YBa2Cu3O7-x and Polycrystalline (Bi–Pb)2Sr2Ca2Cu3O10

We studied three single crystals of YBa2Cu3O7-x, (Y123) with superconducting transition temperature, Tc=62.5, 52, and 41 K, and a highly textured polycrystalline specimen of (Bi–Pb)2Sr2Ca2Cu3O10 (Bi2223), with Tc=108K. Isofield magnetization data were obtained as a function of temperature, with the magnetic field applied parallel to the c axis of each sample. The reversible magnetization data for all samples exhibited a rounded transition as magnetization tended toward zero. The reversible data were interpreted in terms of two-dimensional diamagnetic lowest-Landau-level (LLL) fluctuation theory. The LLL scaling analysis yielded consistent values of the superconducting transition temperatures Tc(H) for the various samples. The resulting scaling data were fit well by the two-dimensional LLL expression for magnetization obtained by Tesanovic and colaborators, producing reasonable values of κ but the fitting parameter ∂Hc2/∂T produced values that were larger than the experimentally determined ones. We performed simultaneous scaling of Y123 data and Bi2223, obtaining a single collapsed curve. The single curve was obtained after multiplying the x and y axis of each scaling curve by appropriate sample-dependent scaling factors. An expression for the two-dimensional x-axis LLL scaling was extracted from theory, allowing comparison of theoretical values of the x-axis scaling factors with the experimental values. The comparison between the values of the x-axis produced a deviation of 40% which suggests that the hypothesis of universality of the two-dimensional LLL fluctuations is not supported by the studied samples. We also observe that Y123 magnetization data for temperatures above Tc obbey a universal scaling obtained for the diamagnetic fluctuation magnetization from a theory considering non-local field effects. The same scaling was not obbeyed by the corresponding magnetization calculated from the two-dimensional LLL theory.

Angular dependence of high field magnetization fluctuation of two-dimensional Bi 2Sr 2CaCu 2O 8 single crystals

We report reversible magnetization data and the scaling for the magnetization obtained for magnetic fields ( H) applied at various tilt angles θ of the dc magnetic field with respect to the c axis in a single crystal of Bi 2Sr 2CaCu 2O 8. Our data show the crossover of the magnetization below the superconducting onset temperature, which indicates a dominant vortex fluctuation.

Temperature dependencies of the upper critical field and the Ginzburg–Landau parameter for single-crystalline NbSe2

Abstract We present the results of magnetization measurements made on a NbSe 2 single crystal for magnetic-field orientations both along and perpendicular to the c -axis of the crystal. The data were analyzed using a recently developed scaling procedure. We show that in the case of NbSe 2 , in addition to evaluating H c2 ( T ), the temperature dependence of the Ginzburg–Landau parameter may be extracted from the reversible-magnetization data. NbSe 2 , whose properties were extensively studied in the past, is used as a test case for the above-mentioned scaling procedure.

Intrinsic parameters of aT*-phaseSmLa0.8Sr0.2CuO4−δsingle crystal and the fluctuation effects deduced from magnetization data

We report the result of a detailed study on the equilibrium thermodynamic properties from the reversible magnetization data of a ${T}^{*}$-phase ${\mathrm{SmLa}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{CuO}}_{4}$ single crystal ${(T}_{c}^{\mathrm{on}}\ensuremath{\approx}24 \mathrm{K}).$ The analysis of those data outside the critical fluctuation region was performed according to the Hao-Clem model, while the data in the critical region were analyzed on the basis of the nonperturbative two-dimensional Ginzburg-Landau lowest Landau level scaling theory developed by Te\ifmmode \check{s}\else \v{s}\fi{}anovi\ifmmode \acute{c}\else \'{c}\fi{} et al. The analysis outside the critical region yields a complete set of intrinsic parameters of this system consisting of the Ginzburg-Landau parameter $\ensuremath{\kappa},$ the thermodynamic critical field ${H}_{c},$ the magnetic field penetration depth $\ensuremath{\lambda},$ the Cooper pairs coherence length $\ensuremath{\xi},$ and the upper critical field ${H}_{c2}.$ We found that the values of ${H}_{c}(T)$ derived from the Hao-Clem model were generally smaller than those obtained from scaling analysis in the critical region. According to the result of analysis in the critical region, these differences are suggested to have their origin in the thermal fluctuation effect evidenced by the existence of a crossing point in the magnetization data at ${T}^{*}=23.25 \mathrm{K},$ right below the onset critical temperature.

Anisotropy of superconducting MgB2 as seen in electron spin resonance and magnetization data.

We observed the conduction electron spin resonance (CESR) in fine powders of MgB2 both in the superconducting and normal states. The Pauli susceptibility is chi(s) = 2.0 x 10(-5) emu/mole in the temperature range of 450 to 600 K. The spin relaxation rate has an anomalous temperature dependence. The CESR measured below T(c) at several frequencies suggests that MgB2 is a strongly anisotropic superconductor with the upper critical field, H(c2), ranging between 2 and 16 T. The high-field reversible magnetization data of a randomly oriented powder sample are well described assuming that MgB2 is an anisotropic superconductor with H(ab)(c2)/H(c)(c2) approximately 6-9.

Determination of irreversibility fields and superconducting parameters inBaPb0.75Bi0.25O3

The dc magnetization of a superconducting ${\mathrm{BaPb}}_{0.75}{\mathrm{Bi}}_{0.25}{\mathrm{O}}_{3}$ sample has been measured as a function of magnetic field and temperature. The results showed that an irreversibility line lies considerably below the superconducting normal phase transition boundary ${B}_{c2}(T),$ similar to that commonly observed in high-temperature superconductors, even though ${\mathrm{BaPb}}_{0.75}{\mathrm{Bi}}_{0.25}{\mathrm{O}}_{3}$ displays a very long coherence length. We attributed the observed large magnetically reversible region to a very small thermodynamic field, which leads to low condensation energies. The reversible magnetization data obtained in the region above the irreversibility line enable us to determine a full set of superconducting parameters for the material.

Upper critical field of four-CuO2-layer TlBa2Ca3Cu4O11+δ single crystals

Measurements of magnetization in the reversible region were performed as a function of temperature on TlBa2Ca3Cu4O11+δ single crystals in magnetic fields up to 5.5T with the field direction applied along the crystalline c-axis. A linear temperature dependence was observed between 70 and 116K for the reversible magnetization and the slope, (dM)/(dT), decreased with increasing field strength. Near Tc (128K), the magnetization showed a rounding. Both the field-dependent dM/dT – values in the linear region and the rounding behavior of the magnetization near Tc indicated that the upper critical field, Hc2, in the TlBa2Ca3Cu4O11+δ system might be very large. Therefore, the reversible magnetization was measured in the low field range, i.e. H≪Hc2, and the traditional method used to obtain the Hc2 value based on the Abrikosov formula near Hc2 was not applicable. By using the model of Hao et al. [Z. Hao, J.R. Clem, M.W. McElfresh, L. Civale, A.P. Malozemoff, F. Holtzberg, Phys. Rev. B 43 (1991) 2844], the reversible magnetization data were analyzed to determine the Ginzburg–Landau parameter κ and the slope of the upper critical field at Tc, (dHc2/dT)|Tc. It was found that κ=109, and Hc2(0)=160T in the TlBa2Ca3Cu4O11+δ crystals with the field parallel to the c-axis.

Magnetic and superconducting properties of doped (Sr,Ca) 10Cu 17O 29-type single crystals

Magnetization, resistivity and electron spin resonance (ESR) measurements have been performed on single crystals of A 10Cu 17O 29 (A=Ca 5.9, Sr 3.5, Bi 0.3, Pb 0.1, Y 0.1, Al 0.1) of the S=1/2 quasi-one-dimensional system, which has both simple chains and two-leg ladders of copper ions. Substantial hole doping has been achieved in the studied crystals, which led to superconductivity with a high critical temperature ( T c≈80 K). The values of the penetration depth have been estimated for temperatures in the range 30–60 K using the reversible magnetization data. A rough estimation of the Ginzburg–Landau parameter, κ, indicates that the superconductivity in the investigated ladder material should be described as an extreme type-II limit. It has been suggested that the superconductivity in the studied system should be related to the two-leg ladders rather than to the chains.

Vortex phases in irradiated highly anisotropic layered superconductors

Resistivity, reversible magnetization, and Josephson plasma resonance (JPR) data for ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ with columnar defects (CD) show that two liquid phases exist above the irreversibility line. They differ by the $c$-axis correlations in pancake positions. We explain the existence of two liquids with different $c$-axis correlations and transition between them in some temperature interval exploring the particle-hole symmetry in the free energy functional for pancakes inside CD. This functional accounts for magnetic interaction of pancakes, their interaction via Josephson coupling, and pinning by CD.

Magnetic and thermal properties of the 116 K superconductor Tl-1223

The ( Tl,Pb,Bi) 1( Sr,Ba) 2Ca 2Cu 3O 9 (Tl-1223) superconducting phase is characterized by means of X-ray diffraction, SEM and optical micrographs, AC susceptibility, resistivity, magnetization M( T, H) both in the reversible and in the irreversible regime up to 5 T, and specific heat near T c up to 14 T. Reversible magnetization data are analyzed using the London model in the low field limit, and the lower critical field is determined from the first flux penetration. Values are given for the upper critical field, μ 0 H c2c(0) = 75 T, the thermodynamic critical field, μ 0 H c(0) = 0.81 T, the lower critical field, μ 0 H c1c(0) = 0.037 T, the penetration depth, λ ab(0) = 1370 A ̊ , the Ginzburg-Landau parameter, κ( T c) = 45, κ(0) = 65, and for the mean-field specific heat jump, ΔC/ T c = 18 mJ/(K 2mol). The variation of the entropy with the field is measured near T c and agrees with magnetization data, thus demonstrating equilibrium conditions. Large magnetic hysteresis is observed only at temperatures below 20 K. The irreversibility line in the high temperature regime follows the functional dependence H irr( T)∞(1− T/ T c) 2. A systematic departure from this behaviour is observed below 70 K, possibly as a result of a phase transformation in the vortex system.

Reversible and irreversible magnetization of the Chevrel-phase superconductorPbMo6S8

Magnetic measurements have been carried out on the hot-isostatically-pressed Chevrel-phase superconductor ${\mathrm{PbMo}}_{6}$${\mathrm{S}}_{8}$ at temperatures from 4.2 K to ${\mathit{T}}_{\mathit{c}}$ and for magnetic fields up to 12 T. The results show that for the ${\mathrm{PbMo}}_{6}$${\mathrm{S}}_{8}$ compound there is a wide magnetically reversible region, between the irreversibility field ${\mathit{B}}_{\mathrm{}\mathrm{irr}}$ and the upper critical field ${\mathit{B}}_{\mathit{c}2}$, on the isothermal magnetic hysteresis curves. The ${\mathit{B}}_{\mathrm{irr}}$(T) line, i.e., the irreversibility line, was found to obey a power-law expression: ${\mathit{B}}_{\mathrm{irr}}$=${\mathit{B}}^{\mathrm{*}}$(1-T/${\mathit{T}}_{\mathit{c}}$${)}^{\mathrm{\ensuremath{\alpha}}}$ with \ensuremath{\alpha}\ensuremath{\approxeq}1.5. Magnetic relaxation measurements revealed that the flux-creep effect in the material studied is substantial and is greater than those observed in conventional metallic alloys, but smaller than in high-temperature superconductors. The existence of the irreversibility line and pronounced flux-creep effect in ${\mathrm{PbMo}}_{6}$${\mathrm{S}}_{8}$ is attributed to the short coherence length of the material. From the reversible magnetization data, the values of the penetration depth, the coherence length, and the critical fields are obtained together with the Ginzburg-Landau parameter \ensuremath{\kappa}. At 4.2 K, the critical current density ${\mathit{J}}_{\mathit{c}}$ is ${10}^{9}$ A ${\mathrm{m}}^{\mathrm{\ensuremath{-}}2}$ at zero field, and decreases to 2\ifmmode\times\else\texttimes\fi{}${10}^{8}$ A ${\mathrm{m}}^{\mathrm{\ensuremath{-}}2}$ at 10 T. Pinning force curves measured at different temperatures obey a Kramer-scaling law of the form: ${\mathit{F}}_{\mathit{p}}$(=${\mathit{J}}_{\mathit{c}}$\ifmmode\times\else\texttimes\fi{}B)\ensuremath{\propto}${\mathit{b}}^{1/2}$(1-b${)}^{2}$, which indicates that the ${\mathit{J}}_{\mathit{c}}$ is limited by one predominant flux-pinning mechanism.

Transport properties of (BiPb)2Sr2Ca2Cu3O10 textured tapes in the mixed state.

We discuss the resistivity, the Hall effect, the Nernst effect, and the magnetization in the mixed state taking the motion of the Abrikosov and Josephson vortices into account. Measurements on a (BiPb${)}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{10}$ tape point out how the contribution of the Josephson vortices to the resistivity ${\mathrm{\ensuremath{\rho}}}_{\mathit{J}}$ prevails at low temperatures and an analytical expression for ${\mathrm{\ensuremath{\rho}}}_{\mathit{J}}$ is proposed. Above the irreversibility line the Hall effect, the Nernst effect, and the magnetization are less affected by the granularity of the material and, at first approximation, can be considered to be intrinsic properties. Starting from this assumption, we calculate the contribution of the Abrikosov vortices to the resistivity ${\mathrm{\ensuremath{\rho}}}_{\mathit{A}}$ using the Nernst effect and the reversible magnetization data. The ${\mathrm{\ensuremath{\rho}}}_{\mathit{A}}$ thus calculated has an order of magnitude close to the values reported in literature for single crystals, and shows an activated behavior with temperature, whose activation energy value is in strict agreement with that measured in epitaxial thin films of Bi(2223) compound.