The pinning characteristics of a single crystal NdBaaCu3Oy superconductor at low （40 K）, intermediate （77.3 K） and high （88 K） temperatures were investigated. The experimental results of the critical current den...The pinning characteristics of a single crystal NdBaaCu3Oy superconductor at low （40 K）, intermediate （77.3 K） and high （88 K） temperatures were investigated. The experimental results of the critical current density dc and the apparent pinning potential u o which estimated from magnetic relaxation measurements are compared with the theoretical analysis based on the flux creep-flow model, taking the distribution of the flux pinning strength into account. The number of flux lines in the flux bundle （g2）, the most probable value of pinning strength （Am）, distribution width of pinning strength （σ-2） and other pinning parameters such as m, γ,δ are determined so that a good fit is obtained between the experimental and theoretical results. The behavior of these parameters is discussed in correspondence to the pinning characteristics of low, intermediate and high temperatures. The observed results are approximately consistent with the theoretical predictions of Brandt et al. model of the order-disorder transition.展开更多
We investigated the effect of processing conditions on the structure and physical properties of the polycrystalline samples of Ca0.8Fe2Se2 prepared via solid state reaction. X-ray diffraction showed that the main phas...We investigated the effect of processing conditions on the structure and physical properties of the polycrystalline samples of Ca0.8Fe2Se2 prepared via solid state reaction. X-ray diffraction showed that the main phase became FeSe when the sintering temperature increased above 350 ℃. The temperature dependence of magnetization （M-T curves） recorded in zero-field-cooled mode by SQUID magnetometer showed some bumps at around 120 K to 140 K. These bumps moved to lower temperatures when the processing temperature increased above 550 ℃. On the other hand, pure FeSe materials produced at 900 ℃ for 24 h showed a sharp superconducting transition Tconset = 8.16 K and the critical current density of 6,252 A/cm2 at 5 K, self-field. SEM results indicated an enhanced grain connectivity.展开更多
文摘The pinning characteristics of a single crystal NdBaaCu3Oy superconductor at low （40 K）, intermediate （77.3 K） and high （88 K） temperatures were investigated. The experimental results of the critical current density dc and the apparent pinning potential u o which estimated from magnetic relaxation measurements are compared with the theoretical analysis based on the flux creep-flow model, taking the distribution of the flux pinning strength into account. The number of flux lines in the flux bundle （g2）, the most probable value of pinning strength （Am）, distribution width of pinning strength （σ-2） and other pinning parameters such as m, γ,δ are determined so that a good fit is obtained between the experimental and theoretical results. The behavior of these parameters is discussed in correspondence to the pinning characteristics of low, intermediate and high temperatures. The observed results are approximately consistent with the theoretical predictions of Brandt et al. model of the order-disorder transition.
文摘We investigated the effect of processing conditions on the structure and physical properties of the polycrystalline samples of Ca0.8Fe2Se2 prepared via solid state reaction. X-ray diffraction showed that the main phase became FeSe when the sintering temperature increased above 350 ℃. The temperature dependence of magnetization （M-T curves） recorded in zero-field-cooled mode by SQUID magnetometer showed some bumps at around 120 K to 140 K. These bumps moved to lower temperatures when the processing temperature increased above 550 ℃. On the other hand, pure FeSe materials produced at 900 ℃ for 24 h showed a sharp superconducting transition Tconset = 8.16 K and the critical current density of 6,252 A/cm2 at 5 K, self-field. SEM results indicated an enhanced grain connectivity.
