Search results for "Pinning force"
showing 8 items of 8 documents
Guided vortex motion in Nb films on facetted substrate surfaces
2003
Abstract Anisotropy of the pinning force in a superconductor can cause a guiding effect on the vortices, which leads to the appearance of new components in the galvanomagnetic quantities of the sample. In this case one can observe an additional odd magnetoresistive component with respect to magnetic field reversal. Furthermore, an even contribution to the Hall voltage is observed. Guided motion of vortices in Nb films on facetted α-Al2O3 (1 0 1 0) was found by measuring the longitudinal and transversal resistivities of three films with transport current directed parallel, perpendicular and at an angle of 45° with respect to the facet ridges. Field inversion was used to separate the even and…
Origin of the fast magnetization relaxation at low temperatures in HTS with strong pinning
2010
The temperature T variation of the normalized magnetization relaxation rate S in high-temperature superconductors (HTS) with strong vortex pinning exhibits a maximum in the low-T range. This was reported for various HTS, and the origin of the faster relaxation at low T appearing in standard magnetization relaxation measurements was usually related to specific pinning properties of the investigated specimens. Since the observed behaviour seems to be characteristic to all HTS with enhanced pinning (generated by random and/or correlated disorder), we show that the S(T) maximum can be explained in terms of classic collective vortex creep. The influence of thermo-magnetic instabilities in the lo…
Magnetization relaxation in the flux-creep annealing regime across the second magnetization peak of disordered YBa2Cu3O7− crystals
2001
Abstract The relaxation of the irreversible magnetization of disordered YBa 2 Cu 3 O 7− x crystals measured in the “flux-creep annealing” regime reveals that across the second magnetization peak (SMP) the barriers against flux motion remain finite at low current densities, which supports the existence of a crossover to a dissipation process involving the plastic deformation of the vortex system. In our experiments, the vortex creep process appears to be exclusively controlled by collective pinning barriers (diverging at low current densities) only below the onset of the SMP, where the vortex system is stable against dislocation formation. The (elastic) collective pinning barriers observed f…
Anomalous behavior of the second magnetization peak inLa1.81Sr0.19CuO4single crystals: Possible influence of two-band superconductivity
2008
We report an anomalous temperature $T$ variation of the field ${H}_{\text{on}}$ for the onset of the second magnetization peak in ${\text{La}}_{1.81}{\text{Sr}}_{0.19}{\text{CuO}}_{4}$ single crystals with the external magnetic field $H$ oriented parallel to the $c$ axis. While the peak field ${H}_{p}$ has a continuous decrease with increasing $T$, ${H}_{\text{on}}$ exhibits a sudden decrease for $T\ensuremath{\sim}11--15\text{ }\text{K}$. This behavior appears to be related to the particular $T$ dependence of the superfluid density in the case of two-band superconductivity affecting the $T$ variation of the elastic energy of the vortex system at low $H$.
Magnetization relaxation in YBCO films with improved supercurrent transport properties
2010
The relaxation of the irreversible magnetization in optimally doped YBCO films with natural and artificial pinning centres was measured in zero-field cooling conditions using SQUID magnetometry. The external magnetic field H was oriented along the c axis. An appropriate method for the determination of the characteristic vortex pinning energy from the normalized vortex-creep activation energy is discussed. This is based on the existence of a crossover elastic (collective) vortex creep at low temperatures T – plastic vortex creep at high T, caused by the T dependent macroscopic currents induced in the sample during magnetization measurements.
Origin of high critical currents in YBa2Cu3O7−δ superconducting thin films
1999
Thin films of the high-temperature superconductor YBa2Cu3O7−δ exhibit both a large critical current (the superconducting current density generally lies between 1011 and 1012 A m−2 at 4.2 K in zero magnetic field) and a decrease in such currents with magnetic field that point to the importance of strong vortex pinning along extended defects1,2. But it has hitherto been unclear which types of defect—dislocations, grain boundaries, surface corrugations and anti-phase boundaries—are responsible. Here we make use of a sequential etching technique to address this question. We find that both edge and screw dislocations, which can be mapped quantitatively by this technique, are the linear defects t…
Domain wall pinning in ultra-narrow electromigrated break junctions
2014
The study of magnetic domain walls in constrained geometries is an important topic, yet when dealing with extreme nanoscale magnetic systems artefacts can often dominate the measurements and obscure the effects of intrinsic magnetic origin. In this work we study the evolution of domain wall depinning in electromigrated ferromagnetic junctions which are both initially fabricated and subsequently tailored in-situ in clean ultra-high vacuum conditions. Carefully designed Ni(80)Fe(20) (Permalloy) notched half-ring structures are fabricated and investigated as a function of constriction width by tailoring the size of the contact using controlled in-situ electromigration. It is found that the dom…
Nondiverging vortex pinning barriers at low current densities across the putative elastic vortex-glass–vortex-liquid transition inYBa2Cu3O7−δfilms
2001
A detailed analysis of the electric field--current density $(E\ensuremath{-}J)$ characteristics of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ films across the putative thermally induced elastic vortex-glass--vortex-liquid transition predicted by the $E(J)$ curve scaling reveals that the expected increase of the collective pinning barriers with decreasing J is cut off in the low-$J$ region, signaling a dissipation process which involves the plastic deformation of the vortex system. The temperature and magnetic field dependence of the pinning barriers at low J does not change across the scaling-predicted glass transition line. For the investigated m…