Vortex pinning by Ni point defects inBi2Sr2Ca(

Abstract

We study the vortex pinning of Bi 2 Sr 2 CaCu 2 O 8ϩ␦ ͑Bi2212͒ single crystals doped with up to 2 at. % of Ni atoms on the Cu position using measurements of the dynamic magnetic relaxation. We find that below an optimum Ni-doping level of about 1 at. % the thermal activation energy for vortex creep and the critical current density definitely increase with the Ni concentration. This proves that Ni point defects contribute to the pinning forces, as expected within the theory of weak collective pinning. At higher Ni concentrations we observe a strong decrease of the activation energy, probably caused by an overlap of the vortex potentials from neighboring Ni sites. The dynamic behavior of the vortex system at low temperatures and magnetic fields is dominated by elastic creep of single vortices whereas at higher temperatures and fields plastic creep of vortex dislocations becomes dominant. The phase with plastic creep grows in the (B,T) plane with increasing strength of the collective pinning forces.

Crystal structure and superconducting properties of hole-doped Ca0.89Na0.11FFeAs single crystals

“…The observed behavior might be dominated by the presence of a crossover from elastic vortex creep at low temperatures to plastic creep at elevated temperatures. A similar flux dynamics, leading to a substantial decrease or even to negative µ values, has been observed in a number of superconducting cuprates and pnictides [41][42][43][44]. In contrast, for Ca 0.6 Na 0.4 Fe 2 As 2 we found a single value for µ = 0.58, which could fit the whole temperature range satisfactorily.…”

Flux pinning and magnetic relaxation in Ga-doped LiFeAs single crystals

“…A similar flux dynamics, leading to substantial decrease or even to negative l values has been observed in a number of superconducting cuprates. 8,[60][61][62] In cuprates, the crossover from elastic to dislocation-mediated plastic creep was attributed to the characteristic field B p , which corresponds to the fishtail peak in the magnetization curve. 60 Similar to cuprates, a crossover from elastic to plastic creep above B p was observed in a number of iron pnictides.…”

Atomic-Scale Quasi-Particle Scattering Resonances in Bi 2 Sr 2 CaCu 2 O 8+δ

“…For these applications, metal hydridation is the existing method above room telnperahlres and below 20 to 40 atm of pressure, but these materials are heavy and expensive (1,2). Cryoadsolption, in which activated carbon is often used as a sorbent, shows its advantages in the nloderate size and weight of carbon, but suffers fi-om the severe conditions (liquid nitrogen tenlperatures and 20 atill of pressure) required to hold the physically adsorbed H2 (3,4). In any case, the H, uptake by these systems is less than 6 weight % ( or 112 kg of H,!m3 (for K-doped CNT).…”