V. Zrubec

Simplified fast method for magnetic characteristics measurement of the HTc superconducting materials

Abstract A simple measuring method and system for fast measurement of HT c superconductors characteristics are described. The measured sample is inserted into a low-frequency magnetic field in the center of two oppositely oriented coplanar coils with different diameters. The coils together with the sample are placed in the vessel with LN 2 which is outside the LHe cryostat. The currents in the coils are set up in such a way that before inserting the sample the compensated state (zero signal on the system output) is reached in the space of the pickup coil of the SQUID 2nd order gradiometer. After inserting the sample the compensation is disturbed and the arising signal is proportional to the equivalent dipole magnetic moment which characterizes the investigated superconducting material. The experimental measuring system reaching a sensitivity of order 10 -7 A m 2 at a frequency of the magnetizing field ⩽1 Hz is described. Measured magnetization hysteretic characteristics of the short-period melted HT c Bi superconductor are given.

Theoretical sensitivity limits of the SQUID system for measuring beam intensities of electrically charged particles in superconductive accelerators

Abstract This paper is aimed at theoretical aspects of the application of superconducting quantum magnetometers (SQMs) to measuring the beam intensities of electrically charged particles accelerated in superconducting accelerators. The characteristics of the antenna system picking up the magnetic field which is induced by the unidirectional component of the flux of the accelerated particles, are examined and the influence of the transfer chain element parameters is analysed. On the basis of derived relationships, the antenna parameters have been optimized, from the viewpoint of their sensitivity and reduction of the output signal dependence upon the beam deviation in the transverse direction. The maximum attainable sensitivity of the measuring system, given by its intrinsic noise, has been determined. Theoretical analysis proves that the sensitivity limit for accelerators with a beam trajectory radius of the order of 10 1 m is of the order of (10 2 –10 3 ) elem. charges/cycle. An example of the calculation of measuring system parameters at given accelerator and SQM parameters is also presented. Principles concerning the elimination of disturbing electromagnetic fields by means of superconductive and ferromagnetic shielding are also highlighted.

The effect of rare earth oxide substitution on the magnetic properties of Tl-based superconductors

Abstract The effects of the heterovalent substitution of the rare earth ions La3+, Sm3+, Pr3+, Dy3+ and of Y3+ into the Ca2+ separating layers on the magnetic properties of (Tl,Pb)-1223 and (Tl,Pb)-1212 superconductors are reported. Nominal compositions of (Tl0.6Pb0.5)(Sr0.8Ba0.2)2(Ca1−xMx)2Cu3O8+δ, where M=La, Sm, Pr, Dy, Y and x=0.0, 0.05, 0.1, 0.15 and 0.2 were investigated. Increasing contents of the rare earth elements enlarged the superconducting Tl-1212 phase in the samples. This led to a decrease of the Tc values. AC and virgin volume magnetization characteristics of all fabricated samples were measured at 77.3 K in magnetic fields ranging from 10−1 to 105 Am−1. A decrease in the content of the Tl-1223 phase affected the magnetization mainly in the range of stronger fields around 105 Am−1. For the lower substitution levels (x=0.05, 0.1) an improvement of the intergrain links was found.

Theoretical sensitivity limits of the compensation method for magnetization characteristics measurement of HTc superconducting materials using LTc SQUID 2nd order gradiometer

Abstract This article deals with theoretical analysis of a fast compensation method of measuring magnetization characteristics using superconductive quantum 2nd order gradiometer suitable for measuring material samples with low magnetic susceptibility in an alternating low-frequency magnetic field. Special attention is paid to measuring magnetization characteristics of HT c superconductors at a temperature of 78K. Transmission and noise properties of the measuring system consisting of LT c SQUID 2nd order gradiometer and magnetization coil system with the sample of HT c superconductive material placed in liquid nitrogen in an external case under an LHe cryostat of a gradiometer are studied. The maximum sensitivity of the system given by noise properties of a superconductive quantum gradiometer, noise parameters of the magnetization magnetic field and environmental noise in the measuring environment is determined. It follows from a theoretical analysis that the spectral density limit of an input equivalent noise magnetic moment of a system placed in a magnetically shielded room with parameters achieved in rooms designed for measuring biomagnetic fields can reach the order of 10 −13 Am 2 Hz −1/2 . Under conditions typical of unshielded magnetic laboratories for measuring weak magnetic fields the order of (10 −8 ÷10 −11 ) Am 2 Hz −1/2 can be achieved theoretically. The measuring process is outlined and parameters achieved with systems in an unshielded environment and examples of measured characteristics of HT c superconductors in an alternating magnetization magnetic field with the frequency 0.1 Hz are cited. The accessibility of a sample for manipulation, general arrangement and a simple measuring process allow quick scanning and recording of magnetization characteristics (a set of five amplitude phased hysteretic curves in a time of ∼2.5 min).

Optimization of noise parameters of SQUID magnetometers with external negative feedback

Abstract The noise and transfer parameters of superconducting quantum magnetometers (SQMs) with external feedback (used in multichannel systems to exclude the crosstalk in the antenna system) are analysed. An input equivalent noise circuit is designed and the relations for its parameters in terms of dependence of spectral density of the magnetometer output voltage noise are derived. The optimum s n ratio conditions in relation to the dependence of antenna inductance are derived. The term input equivalent energy sensitivity is introduced, which enables a simple comparison of the SQMs with external and conventional internal feedback. The procedure of noise parameter measurement and the experimental results supporting the theoretical analysis are given.

Influence of the Tl- and Hg-content on magnetic and transport properties of the Pb, Sr-doped Tl-1223 and Hg-1223 superconductors

Abstract The effects of the thallium and mercury content x on the as-sintered and post annealed samples of M x Pb 0.4 Sr 1.6 Ba 0.4 Ca 2 Cu 3 O 8+ δ {M: Tl (0.32≤ x ≤0.74) or Hg (0.18≤ x ≤0.68)} have been studied by magnetization and transport measurements. For Tl-1223 we have found the optimum Tl doping level to be x =0.53 regarding the grain properties, the content of superconducting phase, the first penetration field H pl wl , the transport ( J c tr ), magnetic intergrain ( J c M ) and intragrain ( J c g ) critical current densities. The critical temperature T c of the as-sintered Tl-1223 sample decreased with increasing Tl content. Post-annealing in oxygen improved the T c for Tl contents of x ≥0.53 and had generally positive effects on the critical current densities. The intergrain properties of the Hg-1223 samples were much worse than those of the Tl-based superconductors.

rf SQUID magnetometer with simplified circuitry

This note contains a brief description of a portable type of magnetometer which uses an rf SQUID. In the simplified electronic circuit no low‐frequency modulation is used.

Study of light nonstoichiometry in Eu-Ba-Cu-O systems

We studied effects of light Eu-Ba nonstoichiometry in Eu-Ba-Cu-O superconducting compounds on their transition, structural, and magnetic properties. Two series of Eu1+xBa2-xCu3O7+δ and Eu1-x Ba2+xCu3O7+δ samples with x = 0, 0.01, 0.02, 0.04, 0.05, 0.07 and 0.1 were synthesized by the solid-state reaction method from Eu2O3, BaCO3 and CuO precursors and sintered at 1050°C for 72 h in flowing oxygen. Structural, transition, and magnetic properties were investigated by means of X-ray diffraction, resistance, mutual inductance, magnetization and optical measurement methods. The Eu-Ba nonstoichiometry in the two series results in different effects on transport, magnetization, grain, intergrain and microstructure properties of the samples in relation to the substitution level of x. All the samples show the values of critical temperature Tc, volume density ρ, and maximum volume magnetization Mmax higher than 91 K, 6.4 g cm-3 and 104Am1, respectively.

Improved system for measurement of the magnetization characteristics of high-temperature superconductors by the compensation method in weak magnetic fields

This article follows the previous publication (1999) of the author where the theoretical sensitivity limits and the basic analysis of the parameters of the superconducting quantum interference device systems for measurement of the magnetization characteristics of high-temperature (HTc) superconductors in ac low-frequency magnetic field with the help of a compensation method were given. It contains the theoretical base for the optimization of such systems and the results achieved by its application in an experimental model of the measuring system. The article deals with the dependence of the spectral sensitivity and the signal-to-noise ratio of the electronic unit of superconducting quantum gradiometer (EU SQG) output on the volume and the susceptibility of the HTc superconducting material sample. It concluded that the chosen dimensions of the pellet shaped sample (diameter 12 mm, thickness 2.5 mm) were optimum for the given measuring system in magnetically unshielded ambient. A method is presented of how ...

Influence of high level Ag doping on the superconducting properties of YBa2Cu3O7/Ag composites☆

Abstract The role of Ag-additions in the synthesis of bulk YBa 2 Cu 3 O 7 is extremely varied. In order to separate and understand some aspects of these introductions, this paper describes the synthesis of two series of bulk samples with different thermal histories as a function of their silver content up to very high loadings (0–80 wt.%), which may have industrial significance. Their morphological and thermal characteristics are discussed and their superconducting properties are studied in detail using AC and DC susceptometry at high and low field. They exemplify the role of silver as flux at high temperatures and as mediator of oxygen transport at lower temperatures.