Determination of the critical current density and the flux pinning force in single crystals YBa2Cu3O7-δ from the magnetization hysteresis cycles

In this study, the magnetization measurements have been performed on high-temperature superconductor's single crystals YBa₂Cu₃O_7-δ at large ranges of temperature T (15-85 K) and in magnetic fields up to 6T at different values of the angle θ between the applied magnetic field and c-axis. The critical current density Jc deduced from the magnetic hysteresis loops by the Bean formula for H parallel to the c-axis (θ=0°), our results have shown that the critical current density Jc was strongly dependent on the applied magnetic field. The pinning force Fp=Jc×μ₀H was determined from magnetization for H//c, however, a plot of the normalized pinning force density fp= Fp/Fpmax as a function of the reduced magnetic field h= H/Hirr at different temperatures have shown good scaling with the form fp ~h^p(1-h)^q, where p and q are scaling parameters. We also found that the point pinning is more dominant than surface pinning under high temperatures.     

YBa2Cu3Oy中氧缺位的磁通钉扎效应

制备了一组不同氧含量(T_cmid>90K)的YBa₂Cu₃O_y单相多晶样品。对其结构、超导电性和磁通钉扎行为的观测结果表明:氧缺位导致临界电流密度J_c和钉扎力密度F_p同时增加,存在一最佳的氧缺位浓度,可使J_c和F_p有最大程度提高。与氧含量y=6.96和6.83时的情况不同,对y=6.94和6.86的样品,其J_c 关键词：     

Flux pinning in columnar-structured and single crystalline MgB2 films

We have investigated the flux pinning effect of columnar grain boundary in columnar-structured and single crystalline MgB₂ films. The MgB₂ films with columnar structure showed much higher J_c than that of single crystalline thin film, and sample having smaller grain size had a higher J_c in high magnetic fields. At 5 K, the MgB₂ film with grain size of 460 nm showed an abnormal double-peak behavior in pining force density, F_p(B), caused by competition of different types of pinning sites, such as planar defects and point defects. Field dependences of F_p in columnar-structured films suggest that the columnar grain boundary is a strong pinning source in the MgB₂ film and it plays a crucial role in enhancing J_c over a wide range of magnetic fields and temperatures.     

Investigation of flux pinning properties of YBCO:BaZrO3 composite superconductor from temperature dependent magnetization studies

Magnetization studies of YBCO:BaZrO₃ composite superconductor have been done over a wide range of temperature and applied magnetic field using MPMS SQUID VSM and the results are compared with that of pure YBCO. The analysis of the observed results indicate that there is considerable improvement in the values of critical current density (J_C) and pinning force density (F_p) of YBCO:BaZrO₃ composite samples as compared to pure YBCO sample in the entire investigated range of applied magnetic field and temperatures ranging from 4 to 77 K. The variation of J_C with reduced temperature t (=T/T_C) for the composite samples has been found to be similar to that of pure YBCO sample indicating similar nature of the vortex interaction with pinning centres in both pure and composite samples. The enhancement in the value of J_C and F_p in the composite samples as compared to pure YBCO sample has been attributed to the increased defect density in the composite samples due to the presence of BZO particles in YBCO matrix.     

The influence of the spectral properties of human skin on the resolution of a Linnik interference microscope

We have studied the Zeeman structure of the 3p5f configuration of SiI and revealed its particular features in the range of variation of the magnetic field from 0 to 60 kOe. In this range, we have found 71 crossings of Zeeman sublevels with ΔM = ±1 and ±2 (M is the magnetic quantum number) and 4 anticrossings of lower F levels with j ₁ = 1/2 (j ₁ is the total angular momentum of the p electron). From splittings of levels in the assured linear range up to 40 Oe, we have calculated gyromagnetic ratios and compared them with their counterparts in the absence of the field.     

Enhanced flux pinning in pulsed laser deposited Y Ba2Cu3O7−δ : BaTiO3 nanocomposite thin films

The effect of incorporation of BaTiO₃(BTO) nanoparticles on the flux pinning properties of pulsed laser deposited YBCO:BTO thin films was studied. Substantial increase in the critical current density (J_C) and the pinning force density (F_p) of the nanocomposite thin films was observed. At 77 K, and zero applied magnetic field, the value of J_C for YBCO and YBCO:BTO (2%) thin films were 2.93 MA/cm² and 6.43 MA/cm², respectively. At the same temperature and an applied magnetic field of 4 T, the value of J_C increases from 3.6×10⁴ A/cm² for YBCO thin film to 2.7×10⁵ A/cm² for YBCO:BTO (2%) nanocomposite thin film. The study of temperature and field dependence of of YBCO and YBCO:BTO thin films indicates similar type of pinning. The lattice mismatch between YBCO and BTO seems to introduce more defects resulting in the improvement of flux pinning properties.     

Magnetic-field oscillations of the critical current and the pinning force in PbTe/PbS semiconductor superlattices and YBa2Cu3O7–δ films

The magnetic-field dependences of the critical current I _c and the pinning force F _p in single-crystal semiconductor PbTe/PbS superlattices on KCl and YBa₂Cu₃O_7–δ films in magnetic fields oriented perpendicular to the plane of the samples or parallel to the current were investigated. Oscillations of I _c and F _p were observed for superlattices with a parallel orientation of the magnetic field and with two directions of the field for the YBa₂Cu₃O_7–δ film. A model was proposed for the vortex structures which correspond to extrema of the pinning force in superlattices. It was shown that the single points (extrema and points of inflection) of the field dependences of F _p for superlattices and a YBa₂Cu₃O_7–δ film appear for critical values of the magnetic field equal to H _cr = (p/q)H ₀, where p and q are integers, H ₀ = 838.37 Oe, and H ₀ = ch/π eR ₀ ² is determined by the length R ₀ = 88.607 nm, somewhat less than the reciprocal of the Rydberg constant R _∞ = me ⁴/π?³ c (R _∞ ^?1 = 91.127 nm). It was inferred on the basis of published data that the temperature and magnetic-field dependences of the properties of superlattices and HTSC materials follow general laws.     

Distinction of spin-glass freezing from superparamagnetic blocking

Experimental results on Eu_xSr_1?xS provide clear evidence for a cooperative phenomenon at the spin-glass transition, as distinguished from ordinary thermal blocking of superparamagnetic clusters. Only below the percolation threshold x_p = 0.13 can single-clusters aspects be separated clearly (superparamagnetic regime). In the spin-glass regime for x >x_p, susceptibility and remanent magnetization are studied near the freezing temperature in dependence on temperature, magnetic field and observation time. The anomalous slow relaxations of the remanent magnetization, which follow a power-law, exhibit a strong variation just near T_f0, the transition temperature deduced from static magnetization measurements. In addition, T_f values derived from ac-_χ measurements are distinctly frequency dependent; the frequency variation decreases towards low frequencies and seems to saturate near the T_f0 value. The strong sensitivity of _χ(T_f) to even small applied fields can be represented by a universal function independent of concentration. All these results emphasize the importance of the interactions among the spin clusters of spin glasses which are partially frustrated.     

Possible observation of the coexistence of superconductivity and long-range magnetic order in NdRh4B4

The ternary rare earth compound NdRh₄B₄ has been studied by means of critical field, low temperature heat capacity, and static magnetic susceptibility measurements. Features in the upper critical field and heat capacity data at 1.31 K and 0.89 K suggest the occurrence of long-range magnetic order in the superconducting state. The temperature dependence of the static magnetic susceptibility follows a Curie-Weiss law with an effective magnetic moment μ_eff = 3.58 ± 0.05 μ_B and a Curie-Weiss temperature θ_p = ?6.2 ± 1.0 K between 20 K and room temperature. However,, magnetization vs. applied magnetic field isotherms suggest the development of a ferromagnetic component in the Nd³⁺ magnetization at low temperatures.     

Current transport property in GdBCO coated conductor with artificial pinning centers in a wide range of temperature,magnetic field up to 27 T,and field angle

We have investigated current transport property in Gd₁Ba₂Cu₃O_7−δ coated conductor with artificial pinning centers in a wide range of temperature, magnetic field, B up to 27 T, and field angle. Due to the additional c-axis correlated pins, critical current density, J_c in B//c was enhanced and the improvement was observed in wide range of B. On the other hand, around B⊥c below 65 K, the angular dependence of n-value showed a valley-like behavior, although the J_c was increasing. In addition, the temperature dependence of the pinning force density defined as J_c × B was not scaled on an expected master curve. These results indicate the pinning in B⊥c is governed by different mechanism below 65 K and high magnetic field.     

Criticality features in ULF magnetic fields prior to the 2011 Tohoku earthquake

The criticality of ULF (Ultra-low-frequency) magnetic variations is investigated for the 2011 March 11 Tohoku earthquake (EQ) by natural time analysis. For this attempt, some ULF parameters were considered: (1) F_h (horizontal magnetic field), (2) F_z (vertical magnetic field), and (3) D_h (inverse of horizontal magnetic field). The first two parameters refer to the ULF radiation, while the last parameter refers to another ULF effect of ionospheric signature. Nighttime (L.T. = 3 am ± 2 hours) data at Kakioka (KAK) were used, and the power of each quantity at a particular frequency band of 0.03–0.05 Hz was averaged for nighttime hours. The analysis results indicate that F_h fulfilled all criticality conditions on March 3–5, 2011, and that the additional parameter, D_h reached also a criticality on March 6 or 7. In conclusion, criticality has reached in the pre-EQ fracture region a few days to one week before the main shock of the Tohoku EQ.     

Strongly enhanced flux pining of GdBCO coated conductors with BaSnO3 nanorods by pulsed laser deposition

We report the effects of BSO addition on the crystallinity, texture, and the field dependency of critical current density (J_c) of GdBCO coated conductors (CCs) prepared by pulsed laser deposition (PLD). Undoped and BSO-doped GdBCO films showed only c-axis oriented growth, and the incorporated BSO nanorods exhibited epitaxial relationship with the GdBCO matrix. In comparison with undoped film, BSO-doped GdBCO film exhibited greatly enhanced J_c and higher pinning force densities in the entire field region of 0–5 T (H//c) at 77 and 65 K. The BSO-doped GdBCO film showed the maximum pinning force densities (F_p) of 6.5 GN/m³ (77 K, H//c) and 32.5 GN/m³ (65 K, H//c), ～2.8 times higher than those of the undoped sample. Cross-sectional TEM analyses exhibited nano-structured BSO nanorods roughly aligned along the c-axis of the GdBCO film, which are believed effective flux pinning centers responsible for strongly improved critical current densities in magnetic fields.     

The anomalously high dielectric constant in narrow-gap semiconductor Cd0.17Hg0.83Te

The measurements performed at 4.2 K with a Rayleigh type UHF interferometer at a frequency ω/2π = 36.0 GHz, using circular polarization, have revealed the existence of an anomaly in the dielectric constant of Cd_0.17Hg_0.83Te (namely, æ ? 175) and demonstrated but a slight dependence of the value upon the magnetic field for $\text{h}\text{?}$ω_H～E_F.     

Effect of thermal treatment on the magnetization processes of nanocrystalline Fe80Ge3Nb10B7 alloys

The dynamic magnetization processes of nanocrystalline Fe₈₀Ge₃Nb₁₀B₇ alloys after annealing at different temperatures are studied through the permeability spectroscopy. Three steps of crystallization are found when amorphous Fe₈₀Ge₃Nb₁₀B₇ alloys are heated from 300to 1200 K. The dominant magnetization process varies with different annealing temperatures. Domain wall bulging is the main magnetization mechanism under weak applied field. When the applied field exceeds pinning field H_p, the depinning-involved domain wall displacement occurs. Different annealing temperature results in different H_p. The lower value of μ′ and high relaxation frequency after heating at 923 and 973 K are due to the strengthened domain wall pinning and the increase of magnetocrystalline anisotropy.     

Selective laser pumping of magnetic sublevels in the hyperfine structure of the cesium atom

The evolution of the populations of the magnetic sublevels of the cesium atom (¹³³Cs isotope) in resonant laser fields with linear polarization is analyzed using the equations for the density matrix. Analytic expressions are derived for stationary populations resulting from laser-induced optical transitions on the hyperfine structure components F _g = 3 ? F _e = 2, 3 and F _f = 4 ? F _e = 3, 4 of lines D ₁ (6² S _1/2 → 6² P _1/2) and D ₂ (6² S _1/2 → 6² P _3/2) depending on the initial values of the populations. The numerical solution of the evolution equations gives the characteristic times of stabilization of the steady regime as functions of laser field intensities and detuning from optical resonance. We determine the sequences of optical transitions increasing (by more than an order of magnitude) the population of the lower sublevel 6² S _1/2 F _g = 3 M = 0 of the “clock” microwave transition F _g = 3 M = 0 ? F _f = 4 M = 0 in the cesium frequency standard, which increases the signal intensity in the recording system by the same proportion.     

Hyperfine interactions in intermetallic rare earth-gallium compounds studied by 111 Cd PAC

Magnetic and electric hyperfine interaction of the nuclear probe ¹¹¹In/¹¹¹Cd in intermetallic compounds of the rare earth-gallium system have been investigated by perturbed angular correlation (PAC) spectroscopy. The PAC measurements, supported by X-ray diffraction, provide evidence for a marked phase preference of ¹¹¹In for hexagonal RGa₂ over orthorhombic RGa and of RGa₃ with the L12 structure over RGa₂. In the case of SmGa₂, the magnetic hyperfine field B_hf, the electric quadrupole interaction and the angle β between B_hf and the symmetry axis of the electric field gradient have been determined as a function of temperature. The angle β?=?0 is consistent with the results of previous magnetization studies. Up to T?≤?17 K the magnetic hyperfine field has a constant value of B_hf?=?3.0(2) T. The rapid decrease at higher T gives the impression of a first-order transition with an order temperature of T_N?=?19.5 K. In the RKKY model of indirect 4f interaction the ratio T_C/B_hf(0) is a measure of the coupling constant. For ¹¹¹Cd:SmGa₂ (T_C/B_hf(0)~6.5 K/T) this ratio is significantly smaller than for the same probe in other R intermetallics (SmAl₂ ~9.5 K/T, Sm₂In ~13.5 K/T).     

Study of magnetic flux pinning in granular YBa2Cu3O7 − y /nanoZrO2 composites

In this work, the effect of ZrO₂ nanoparticles prepared in a low-pressure arc discharge plasma on magnetic flux pinning of granular YBa₂Cu₃O_{7 ? y} /nanoZrO₂ composites has been studied. It has been shown that the ZrO₂ nanoparticles do not change the superconducting transition and the microstructure of superconductors. At a temperature of 5 K, the addition of 0.5 and 1 wt % of ZrO₂ nanoparticles may lead to the additional effect of magnetic flux pinning and the increase in the critical current density J _c. The J _c value for composites with 1 wt % is two times larger than that for the reference sample. The fishtail effect is observed for YBa₂Cu₃O_{7 ? y} /nanoZrO₂ composites at the temperatures of 20 and 50 K. The problems associated with the additional effect of magnetic flux pinning of granular YBa₂Cu₃O_{7 ? y} /nanoZrO₂ composites and the appearance of the fishtail effect have been discussed.     

Electrical resistivity and magnetic investigations of the orthorhombic Tb(Ni,Cu)2 system

The orthorhombic Tb(Ni, Cu)₂ and Gd(Ni, Cu)₂ systems (CeCu₂ structure) are closely similar according to electrical resistivity and magnetic results. The Tb(Ni_xCu_1?x)₂ system presents a transition from antiferromagnetism (AF) for x ? 8% Ni to ferromagnetism (FM) for x > 8% Ni. The CeCu₂ structure becomes unstable for x > 45% Ni. The AF samples show metamagnetism at 4.2 K with critical fields. Hysteresis, which occurs for all samples at 4.2 K, is attributed to intrinsic pinning due to large anisotropy where the mechanism for the AF range is analogous to intrinsic pinning of narrow domain walls in FM samples.Spin disorder resistivity measurements show a discontinuity at the AF-FM transition composition for both the Tb and Gd systems. This is due to a step up of the residual resistivity at 4.2 K as a result of AF ordering. This interpretation is confirmed by applying a magnetic field to destroy the AF ordering.     

Antiferromagnetic resonance spectrum in LaMnO3: Interrelation of the orbital structure and the magnetic properties

The relation between the orbital ordering and magnetic structure of the crystal LaMnO₃ is investigated. The dependence of the exchange parameters on the angle Φ of the orbital structure is determined. When the isotropic exchange interaction and the single-ion anisotropy, which depends on the angle Φ and the rotational distortions, are introduced into the spin Hamiltonian, a four-sublattice structure (A _X, F _Y, G _Z) is obtained with orientation of the magnetic moments of the sublattices near the long axis of the orthorhombic cell of the crystal in the basal plane of the crystal (A _X ? G _Z, F _Y). The effect of a magnetic field on the magnetic structure and the antiferromagnetic resonance spectrum are investigated taking account of the nonequivalent, anisotropic, orbitally-dependent g tensors. The spin-flop and spin-flip transition fields are calculated.     

Existence of double-pinning force maxima for a single pinning mechanism

Critical current measurements on a cold rolled Pb₆₀In₄₀ foil show two pinning maxima, one close to H_c2 in the neighborhood of h = 0.95, and the other at low fields around h = 0.15. The high field pinning force maximum shifts to lower fields, and the low field maximum shifts to higher fields with increasing pinning strength. The data is explained in terms of Kramer's pinning force model incorporating Brandt's expression for C>₆₆.