An AC susceptometer for the characterization of large, bulk superconducting samples

The main purpose of this work was to design, develop and construct a simple, low-cost AC susceptometer to measure large, bulk superconducting samples (up to 32 mm in diameter) in the temperature range 78-120 K. The design incorporates a double heating system that enables a high heating rate (25 K/hour) while maintaining a small temperature gradient (< 0.2 K) across the sample. The apparatus can be calibrated precisely using a copper coil connected in series with the primary coil. The system has been used successfully to measure the temperature dependence of the AC magnetic properties of entire RE-Ba-Cu-O [(RE)BCO] bulk superconducting domains. A typical AC susceptibility measurement run from 78 K to 95 K takes about 2 hours, with excellent temperature resolution (temperature step ~ 4 mK) around the critical temperature, in particular.Comment: 25 pages, 7 figures. Accepted for publication in Measurement Science and Technolog

Trim Simulations and Possible Studies for Edge-on Ion Irradiation of Electron Microscope Specimens

A TRIM code has been modified to simulate a special technique, first described at the Spring 92 MRS Meeting, for in-situ transmission electron microscope (TEM) experiments involving simultaneous ion irradiation, in which the resultant phenomena are observed as in a cross-section TEM specimen without further specimen preparation. Instead of ion-irradiating the film or foil specimen normal to the major surfaces and observing in plan view (i.e., in essentially the same direction), the specimen is irradiated edge-on (i.e., parallel to the major surfaces) and is observed normal to the depth direction of the irradiation. Results of calculations utilizing the modified TRIM code are presented for cases of 200 and 500 keV Co impinging onto the edge of Si films 200 and 600 nm thick. Limitations of the technique are discussed and feasibility of experiments involving implantation of Co into Si and the formation of CoSi{sub 2}, which employ this technique, are briefly discussed. 10 refs, 3 figs

Defect cascades produced by neutron irradiation in YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} superconductors

The defect cascades produced by fast neutron irradiation of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} single crystals were studied by transmission electron microscopy. The visible defects were found to have sizes between 1 and 5 rim. Defect densities were obtained as a function of neutron fluence between 2 and 8{times} 10{sup 21} m{sup {minus}2} (E>0.1 MeV). The measured defect density scales linearly with fluence and amounts to 1{times}10{sup 22} m{sup {minus}3} at a neutron fluence of 2{times}10{sup 2l} m{sup {minus}2}. The defect stability was studied at room temperature and through annealing to 400{degrees}C

Magnetic flux penetration and creep in BSSCO-2223 composite ceramics

We have experimentally investigated the magnetic flux penetration through a Bi-2223 polycrystalline superconductor synthesized by a classical solid-state reaction method. Electrical resistance, AC susceptibility, the Campbell method and magnetic flux waveform recordings have been analysed and compared in order to separate clearly intergrain and intragrain contributions. The AC susceptibility frequency dependence has been also examined at T = 77 K in a broad field range (0.01 G < B-AC < 100 G) The activation energy as a function of AC applied magnetic field is found to present a pronounced minimum for an induction (8 G) corresponding to full magnetic flux penetration through the intergranular matrix

Enhancements of the Critical Currents of YBaCuO Single Crystals by Neutron (n) and Proton (p) Irradiation

We present results of magnetization hysteresis and [Tc] measurements of neutron and proton irradiated YBaCuO single crystals. The crystals used for comparison were irradiated to a fluence of 2[times]10[sup 7]n/cm[sup 2] (n,E [gt] 0.1MeV) and 1[times]10[sup 16]p/cm[sup 2] (p,E=3.5MeV). The critical currents at 1T and 10K are enhanced by a factor of 5 for the neutron irradiated and a factor of 9 for the proton irradiated sample respectively. After irradiation the crystals were annealed at 100, 200 and 300C for 8h each in air. Following each annealing step the critical temperature and the magnetization hysteresis at 10 and 70K was measured. Upon annealing, we observe a decrease of the critical currents, which is more pronounced for the proton irradiated sample. This decrease is related to the removal of point defects or their small clusters. Thus, their contribution to pinning can be studied. The critical temperature decreases after both types of irradiation by about 0.5K and is fully recovered after annealing

Influence of the shielding currents lengthscale and anisotropy effects on the magnetic flux profiles of high-temperature superconductors

peer reviewedThe so-called "magnetic flux profile" AC inductive technique is a powerful method for determining the critical current density Jc of bulk superconductors. In this work we aim at reporting analytical expressions for magnetic flux profiles of superconducting rectangular samples exhibiting a critical current density anisotropy. The results are used for examining the error resulting from approximating a rectangular cross-section by an "infinite cylinder" or "infinite slab" geometry. It is found that such approximations can lead to an artificial curvature of the flux profiles and errors of 10%–20% in the determination of Jc. Next, the effects of how planar defects (cracks, platelet boundaries,...) affect the magnetic flux profile signal are discussed. It is found that the magnetic flux profiles are much sensitive to the lengthscale of shielding currents, thereby providing means of investigation of the typical size of induced current loops in bulk superconductors. Finally some illustrative flux profile data measured on a bulk, large grain melt-processed YBCO single domain exhibiting Jc anisotropy are presented and discussed in relation with theoretical predictions

Enhancements of the Critical Currents of YBaCuO Single Crystals by Neutron (n) and Proton (p) Irradiation

We present results of magnetization hysteresis and {Tc} measurements of neutron and proton irradiated YBaCuO single crystals. The crystals used for comparison were irradiated to a fluence of 2{times}10{sup 7}n/cm{sup 2} (n,E {gt} 0.1MeV) and 1{times}10{sup 16}p/cm{sup 2} (p,E=3.5MeV). The critical currents at 1T and 10K are enhanced by a factor of 5 for the neutron irradiated and a factor of 9 for the proton irradiated sample respectively. After irradiation the crystals were annealed at 100, 200 and 300C for 8h each in air. Following each annealing step the critical temperature and the magnetization hysteresis at 10 and 70K was measured. Upon annealing, we observe a decrease of the critical currents, which is more pronounced for the proton irradiated sample. This decrease is related to the removal of point defects or their small clusters. Thus, their contribution to pinning can be studied. The critical temperature decreases after both types of irradiation by about 0.5K and is fully recovered after annealing