Düzgün, İbrahim; Çelebi, Selahattin

In this study, the remanent magnetization and magnetic relaxation behaviour of Bi-2223/Ag superconducting tapes fabricated using the Powder-In-Tube (PIT) method were investigated. Measurements were conducted at a fixed temperature of 30 K, both under various field cycling amplitudes and in constant magnetic field conditions to analyse time-dependent magnetization. The remanent magnetization values obtained after full magnetic cycles were normalized and compared with theoretical predictions based on the extended critical state model. Additionally, magnetic relaxation curves were recorded at 30 K to evaluate flux creep characteristics. A clear logarithmic decay in magnetization was observed, indicating the coexistence of at least two distinct pinning regimes. These results contribute to a deeper understanding of flux dynamics and magnetic stability in Bi-2223/Ag PIT tapes for practical superconducting applications.

Öztürk, Ali; Düzgün, İbrahim; Başoğlu, Mehmet; Çelebi, Selahattin

Partial Re (rare earth elements: Lu, Yb and Dy) substituted YBaCuO (123) superconductors synthesized by solid-state reaction (SSR) procedure have been investigated via x-ray diffraction, scanning electron microscopy, a.c. magnetic susceptibility, and d.c. magnetization, and calculations. The measurements of a.c. magnetic susceptibility have been carried out at constant a.c. field amplitude and constant frequency for the samples studied. The temperature dependence of intergranular critical current density (Jcm) has been estimated from the a.c. magnetic susceptibility data. The d.c. magnetization measurements were performed at the temperatures of 5 K, 20 K, and 77 K separately. The variation of critical current density (Jc) with magnetic field (μ0H) has been evaluated from the d.c. magnetization data by using upper and lower branch of the major hysteresis curve. Lu substituted Y0.5Lu0.5BCO (123) sample shows higher critical current density than Yb and Dy substituted samples at low-temperature (lower than 77 K) regions.

Öztürk, Ali; Düzgün, Ibrahim; Çelebi, Selahattin

Measurements of the ac susceptibility in a commercial Bi:2223/Ag tape for some different ac magnetic field amplitudes, Hac, in the presence of bias magnetic field Hdc directed along Hac are reported. It is found that the peak values of the imaginary component of ac susceptibility χ″max versus Hac trace a valley for the orientation where applied field Ha perpendicular to wide face of the tape total. We note that the observation of the valley depends on various parameters such as field dependence parameter n in the critical current density, in the simple power law expression jc = α(T)/Bn, choice of the bias field Hdc together with selected ac field amplitudes Hac, and dimension and geometry of sample studied. Our calculations based on critical state model with jc = α(1 - T/Tcm)p/Bn using the fitting parameters of n = 0.25, p = 2.2, Tcm = 108 K gives quite good results to compare the experimental and calculated curves.

Öztürk, Ali; Doğan, Mustafa; Düzgün, İbrahim; Çelebi, Selahattin

The effect of dysprosium (Dy) doping on yttrium barium copper oxide (YBCO) prepared by conventional solid-state reaction method has been investigated by means of XRD, AC susceptibility, and DC magnetization measurements. AC susceptibility measurements for sintered YBCO pellets have been performed as a function of temperatures at constant frequency and AC field amplitude in the absence of a DC bias field. DC magnetization measurements were done at 5, 20, and 77 K upon zero field cooling (ZFC) process. The magnetization measurements showed a paramagnetic behavior existing at high magnetic fields. The magnetic field dependence of critical current density of the samples has been estimated from DC magnetization data. The partial Dy substitution for Y on YBCO superconductors improves the bulk critical current density at high magnetic fields and at high-temperature regions (higher than 20 K).