The Effect of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Buffer Layer on the Magnetic Properties of Melt-Processed YBCO Superconductor

In this study, two kinds of melt-processed YBCO samples (Y1050-1 and Y1050-2) grown on a buffer layer of Y₂O₃ addition were fabricated. The compacted powders were located on a crucible with Y₂O₃ powder freely poured and a buffer layer of pressed Y₂O₃ to avoid liquid to spread on the furnace plate. The superconducting transition temperature was determined by a standard four-point method at temperatures between 40 and 100 K. The transition temperatures of Y1050-1 and Y1050-2 were found to be 91.6 and 92.9 K at zero magnetic fields, respectively. The magnetization measurements were performed using a vibrating sample magnetometer (VSM) on the same system at 5, 40, and 77 K. The critical current densities for Y1050-1 and Y1050-2 samples were determined to be 6.5×10³ and 5.6×10³ A/cm² at 77 K in zero magnetic fields, respectively. The trapped magnetic field measurements of the samples were performed by using a Hall probe scanning device and a Fe–Nd–B permanent magnet at 77 K. It was found that the trapped magnetic field of the Y1050-1 sample is higher than that of the Y1050-2 sample.     

Microstructure Study at Different Thicknesses of Disc-Shaped YBa2Cu3O7?x Prepared by FQMG Method

The flame-quench-melt-growth (FQMG) method was used for the preparation of bulk YBa₂Cu₃O_7?x (Y123). Both the superconducting and nonsuperconducting regions changing with thickness of superconducting sample were determined by X-ray diffraction (XRD) patterns and also observed at micrographs taken by the polarized optical microscope. It was observed that superconducting forming ratio which was examined for different thicknesses of the sample ranging from 6.54 to 1.58 mm strongly enhanced. This means that a region near the top surface of the sample contains more superconducting phase than the other regions. These observations would be helpful in designing and manufacturing the practical applications of YBCO systems.     

Investigation of the dependency of the upper critical magnetic field on the content x in Y1−xYbx/2Gdx/2Ba2Cu3O7−y superconducting structures

The Y_1−xYb_x/2Gd_x/2Ba₂Cu₃O_7−y superconducting samples for x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared by using the solid-state reaction technique. Resistivity measurements of the samples were performed in QD–PPMS system under different magnetic fields up to 5 T in zero fields cooling regime. Using the resistivity data, the upper critical magnetic field H_c2(0) at T = 0 K for 50% of R_n was calculated by the extrapolation H_c2(T) to the temperature T = 0 K. The coherence length in T = 0 K were calculated from H_c2(0) and the effects of x in the composition on both the coherence length and the upper critical magnetic field were examined. The results showed that H_c2(0) varied from 84.05 to 122.26 T with the content x. The upper critical magnetic field in the temperature T = 0 K slightly decreased with increasing the content x. Using the content x, the upper critical magnetic field can be controlled and this can be used in the superconductivity applications.     

Effects of Initial Cooling Conditions and Measurement Heights on the Levitation Performance of Bulk MgB_{2} Superconductor at Different Measurement Temperatures

The levitation properties of MgB \(_{2}\) prepared by hot press at 200  \(^{\circ }\) C and then pellet/closed tube method has been investigated. The vertical and lateral levitation forces ( \(F_{z}\) and \(F_{x})\) on a cylindrical NdFeB permanent magnet (PM) below a disk-shaped bulk MgB \(_{2}\) were measured during the vertical and lateral traverses of the PM in different cooling heights (CHs) and measurement heights (MHs) at temperatures of 20, 25 and 30 K to investigate the effect of the initial CH and MH on the levitation performance of MgB \(_{2}\) . For temperatures below 30 K, it was observed that \(F_{z}\) increases with increasing CH. However, a minute variation in \(F_{z}\) and a big hysteresis loop are observed at 30 K. From the lateral traverses, it was obtained that the \(F_{z}\) with attractive character increases with decreasing MH and the hysteresis effect increases for small MHs due to the increment of the magnetic field intensity which the sample feels with decreasing MH. In addition, it was seen that the character of \(F_{x}\) varies depending on both MH and measurement temperature. The higher hysteresis obtained in \(F_{x}\) than in \(F_{z}\) during lateral traverses implies that the motion of the flux lines in MgB \(_{2}\) is especially in lateral rather than vertical direction. Finally in this study, it was shown that the levitation performance of MgB \(_{2}\) depends not only on the measurement temperature but also on the CH and MH conditions. These results can be useful for optimizing the levitation performance of MgB \(_{2}\) superconductors for potential applications.     

Magnetic Characterization of SiC Doped Bulk MgB2 Superconductor

Flux pinning is a very significant mechanism to improve critical current density in MgB₂ for many applications, such as developing the performance of wires and tapes. In this study, we have done a systematic study of SiC inclusions in the main matrix of MgB₂. Sample production in the form of MgB_2?x (SiC) _x was carried out by using solid state reaction method (x=0,0.01,0.02,0.04,0.06,0.10) in the argon atmosphere. The structural and magnetic properties of the prepared samples were investigated. Structural characterization of samples was performed by the X-ray powder diffraction (XRD) technique and the Scanning Electron Microscopy (SEM) measurements. Magnetic properties were determined by M?CH loops, magnetization-temperature (M?CT), and AC susceptibility measurements. The T _c of the samples was determined by the M?CT measurements while the J _c is determined through the M?CH measurements. SiC inclusions up to some ratios (x=0.06) increase the critical current density by up to about 50%, while the critical temperature T _c remains unchanged in compatible with the literature.     

The Effect of Y2O3 on AC Susceptibility Measurements of MPMG YBCO Superconductor

In this study, two kinds of melt-powder-melt-growth (MPMG) YBCO sample grown on a buffer layer of Y₂O₃ addition were fabricated. The compacted powders were located on a crucible with Y₂O₃ powder freely poured and a buffer layer of pressed Y₂O₃. AC susceptibility measurements of the samples as a function of temperature was reported for several different AC magnetic-field amplitudes (H _ac ) in the presence of static bias magnetic field (H _b ) directed along H _ac . The loss peaks are found to shift towards lower temperatures as the AC field strength is increased. The frequency effect on the AC susceptibility was also measured. As the frequency increases, the peak temperature shifts to higher temperature. This effect can be interpreted in terms of flux creep.     

Magnetic Properties of YBCO Single-Crystal Grown on Y2O3 Layer by a Cold Top-Seeding Method

In this work, single-crystal samples 20 mm in diameter were grown by a cold top-seeding method. In order to study the effect of an Y₂O₃ buffer layer, a compacted precursor was located in a crucible on a buffer layer of freely poured Y₂O₃ powder. The YBCO bulk samples were carefully prepared in the same chemical composition. In order to examine the homogeneity of the samples, rectangular specimens were cut from a sample. The structural orientation of the specimens was measured by a X-ray diffractrometer (XRD). The microstructure was observed with a Scanning Electron Microscope (SEM). The magnetic properties were measured using a Vibrating Sample Magnetometer (VSM) at 77 K with the applied magnetic field parallel to the c-axis. As a result only (00l) peaks were observed in X-ray diffraction data, indicating that all specimens are highly oriented with the c-axis perpendicular to the top surface. Also the cut samples exhibited very fine Y211 inclusion distributed in the bulk sample observed in SEM micrographs. The critical current density J _c (A/cm²) has been estimated by the extended Bean model. The maximum value of the critical current density at 77 K is 5.2×10⁴ A/cm² in a self-field. The trapped magnetic field measurements of the samples were performed by using Hall probe scanning device with static field of 0.5 T at 77 K. The single-domain sample exhibits a trapped field of 1140 G at 77 K.     

Short communication: early detection of mastitis using infrared thermography in dairy cows

Infrared thermography (IRT) absorbs infrared radiation and generates images based on the amount of heat generated. It has been used in human medicine for diagnosis of various cancers. This experiment was conducted to determine if IRT had merit for early detection of subclinical mastitis in dairy cows. Milk sample and skin surface temperature (SST) were simultaneously evaluated using the California Mastitis Test (CMT) and IRT for each quarter in 94 dairy cows (49 Brown Swiss and 45 Holstein). Average days in milk (DIM) and milk production were 93 ± 37 d and 16 ± 2.2 kg (mean ± SD) and their ages ranged from 4 to 8 yr. There was a strong correlation between SST and CMT score (r = 0.92). Average SST was 33.19, 34.08, 34.99, and 36.15°C for quarters with the CMT score of 0 (n = 156), +1 (n = 116), +2 (n = 80), and +3 (n = 24), respectively. This association was best described by a linear model as follows: y = 0.94x + 33.17, R² = 0.85, where y = SST and x = CMT score. Changes in rectal temperature (RT) due to the CMT score were minor (y = 0.09x + 38.39, R² = 0.07, where y = RT and x = average CMT score). In conclusion, RT may not confirm mastitis. However, IRT is sensitive enough to perceive changes in SST in response to varying degrees of severity of the mammary gland infection as reflected by the CMT score, suggesting that as a noninvasive tool, IRT can be employed for screening dairy cows for mastitis.