اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدComparative study of transport and magnetic Jc in the polycrystalline iron-based superconductor NdFeAsO{0.88}F{0.12}
440
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Polycrystalline NdFeAsO0.88F0.12 superconductors prepared by high pressure (HP) and ambient pressure (AP) method were comparatively studied by magnetization and transport measurements. Upper critical field (Hc2), irreversibility field (Hirr) and the anisotropy parameter were estimated from resistance transition curves. The broadening of transition width was observed, and ascribed to both Hc2 anisotropy and superconductivity inhomogeneity of samples. Magnetic hysteresis loops (MHLs) in low fields were measured to detect the trace of weak-link behavior. The reclosed hysteresis loops in low fields manifest that there are weak-links in both samples. Magnetization critical current density Jcm were derived from MHLs. High-pressure synthesized sample shows higher Jcm. However, by means of direct transport I-V measurements, transport critical current density Jct was very low. The Jct values for two samples are comparable. Large discrepancies between Jcm and Jct also indicate that there are weak-links in both samples. The relative mechanism is discussed in detail.
قيم البحث
اقرأ أيضاً
We investigated the temperature dependence of the density-of-states in the iron-based superconductor SmO_1-xF_xFeAs (x=0, 0.12, 0.15, 0.2) with high resolution angle-integrated photoemission spectroscopy. The density-of-states suppression is observed
with decreasing temperature in all samples, revealing two characteristic energy scales (10meV and 80meV). However, no obvious doping dependence is observed. We argue that the 10meV suppression is due to an anomalously doping-independent normal state pseudogap, which becomes the superconducting gap once in the superconducting state; and alert the possibility that the 80meV-scale suppression might be an artifact of the polycrystalline samples.
The new rare-earth arsenate superconductors are layered, low carrier density compounds with many similarities to the high-Tc cuprates. An important question is whether they also exhibit weak-coupling across randomly oriented grain-boundaries. In this
work we show considerable evidence for such weak-coupling by study of the dependence of magnetization in bulk and powdered samples. Bulk sample magnetization curves show very little hysteresis while remanent magnetization shows almost no sample size dependence, even after powdering. We conclude that these samples exhibit substantial electromagnetic granularity on a scale approximating the grain size, though we cannot yet determine whether this is intrinsic or extrinsic.
Magneto-optical imaging was used to study the local magnetization in polycrystalline NdFeAsO$_{0.9}$F$_{0.1}$ (NFAOF). Individual crystallites up to $sim200times100times30$ $mu m^{3}$ in size could be mapped at various temperatures. The in-grain, per
sistent current density is about $jsim10^{5}$ A/cm$^{2}$ and the magnetic relaxation rate in a remanent state peaks at about $T_{m}sim38$ K. By comparison with with the total magnetization measured in a bar-shaped, dense, polycrystalline sample, we suggest that NdFeAsO$_{0.9}$F$_{0.1}$ is similar to a layered high-$T_{c}$, compound such as Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ and exhibits a $3Dto2D$ crossover in the vortex structure. The 2D Ginzburg parameter is about $Gi^{2D}% simeq10^{-2}$ implying electromagnetic anisotropy as large as $epsilon sim1/30$. Below $T_{m}$, the static and dynamic behaviors are consistent with collective pinning and creep.
The doping and energy evolution of the magnetic excitations of the electron-doped cuprate superconductor Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-delta}$ in the superconducting state is studied based on the kinetic energy driven superconducting mechanism. It
is shown that there is a broad commensurate scattering peak at low energy, then the resonance energy is located among this low energy commensurate scattering range. This low energy commensurate scattering disperses outward into a continuous ring-like incommensurate scattering at high energy. The theory also predicts a dome shaped doping dependent resonance energy.
We present results of LDA calculations (band structure, densities of states, Fermi surfaces) for possible iron based superconductor BaFe2Se3 (Ba123) in normal (paramagnetic) phase. Results are briefly compared with similar data on prototype BaFe2As2
and (K,Cs)Fe2Se2 superconductors. Without doping this system is antiferromagnetic with T_N^{exp}~250K and rather complicated magnetic structure. Neutron diffraction experiments indicated the possibility of two possible spin structures (antiferromagnetically ordered plaquettes or zigzags), indistinguishable by neutron scattering. Using LSDA calculated exchange parameters we estimate Neel temperatures for both spin structures within the molecular field approximation and show tau_1 (plaquettes) spin configuration to be more favorable than tau_2 (zigzags).
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
