Angular Dependence Of Critical Currents Research Articles

Formation mechanism of BaZrO3 nanoparticles in Y1−xSmxBa2Cu3Oy-coated conductors derived from trifluoroacetate metal–organic deposition

Grains of BaZrO3 (BZO) in REBa2Cu3Oy (REBCO) films exhibit microstructural differences, depending on whether they weredeposited by pulsed-laser deposition (PLD) or metal–organic deposition (MOD). In orderto understand the origins of these differences, we examined the formation mechanism ofBZO nanoparticles in the MOD process with detailed observations of the quenchedfilms by transmission electron microscopy. The BZO nanoparticle was found toform in the precursor during the temperature ramp prior to the formation of theY1−xSmxBa2Cu3Oy (YSmBCO) crystals. The YSmBCO grew layer by layer while entrapping the BZOparticles, which resulted in random dispersion of the BZO particles in the YSmBCO layer.Consequently, uniformly dispersed BZO nanoparticles were formed in the YSmBCO matrixderived from the TFA-MOD process. These findings indicate that a key factor in achievingfine dispersion of BZO nanoparticles in the superconducting matrix is strongly related tonucleation of the BZO phase crystals in the precursor before growth of the YSmBCO layer,which is unique to the MOD process. In subsequent testing, YSmBCO-coatedconductors with uniformly dispersed and densely concentrated BZO nanoparticlesshowed striking isotropic magnetic-field angular dependence of critical currents.

Angular dependence of critical currents in YBa2Cu3O7-δ vicinal films

The angular dependence of the critical current density in a patterned 8° vicinal thin film of YBa2Cu3O7-δ has been investigated. The transport critical currents were measured on a T track under a variable Lorentz force and under a maximum Lorentz force configuration at different temperatures and fields. The expected critical current minima due to channelling of vortices were observed. String and pancake forces per unit length have been determined.

Model for the angular dependence of critical currents in technical superconductors

We propose a model for the effect of anisotropic pinning on the criticalcurrents in superconductor wires as a function of the direction of an externalmagnetic field. The model emphasizes the statistical distribution of the pinningencountered by a vortex as determining the functional forms observed. Ifwe assume anisotropic defect populations with normal distributions of pinningthen we can derive exact functions for the critical current as a function of angle:Jc(θ). The model predicts that the combination of extended defects in thec-axisand ab-plane directions can lead to peaks at intermediate angles. The predicted forms agree wellwith experiments on superconductors with layered structures including cases wherepeaks occur at intermediate angles. The results suggest that common features ofJc(θ) can be identified with combinations of defects. We discuss some implications of thestatistical model including a possible sample thickness dependence of criticalcurrents.

Angular dependence of critical currents across YBa 2Ca 3O 7− δ low-angle grain boundaries

The angular dependence of the transport critical current density J c across an artificial 5° [0 0 1]-tilt grain boundary (GB) in a YBa 2Ca 3O 7− δ thin film was investigated. The magnetic field was rotated in the ab-plane of the film. Four intragrain tracks were available crossing the GB at 90°, 60°, 45° and 30°. Flux channeling was found at all grain boundary tracks in a symmetric angular interval around the GB direction. The contribution of flux cutting to the critical current was evaluated for the 60° track. Nearly no dependence on the applied magnetic field, but a strong variation with temperature was found.

Angular dependence of spin torque critical currents for CPP-GMR read heads

This paper employs (analytical) micromagnetic modeling to derive expressions for the critical current at the onset of spin-transfer-torque (STT) instability in CPP-GMR read heads, as a function of the relative angle between the free and reference layer magnetizations, including a general angular dependent STT coefficient. Experimental measurement of the angular dependence of the critical currents are made on 50-nm-sized CPP-GMR devices with synthetic antiferromagnet pinned layers, and fabricated using e-beam lithography. The results are consistent with prior theoretical models, but indicate perhaps unanticipated implications for read head operation.

Influence of heat treatment on the properties of Bi 1.8Pb 0.2Sr 2Ca 2Cu 3O x ceramics and Ag-sheathed tapes

Optimization of a heat treatment temperature is applied to bare Bi 1.8Pb 0.2Sr 2Ca 2Cu 3O x ceramics as well as to Ag-sheathed tapes prepared by the powder in the tube method. We discuss structural differences observed by SEM and the phase content and FWHM of rocking curves obtained by X-ray diffraction. Further, we compare the superconducting transition temperature of short samples measured by a.c. susceptibility and the critical current anisotropy measured by the four probe method. The effect of the Ag-envelope as oxygen barrier is shown comparing the differences in the width of transition temperature. The difference in the angular dependence of critical currents reflects not only the texture but also the path in which the current is flowing.

Anisotropy and angular dependence of critical currents in rectangular Nb3Sn superconductors made by the bronze method

An experimental study of the critical current angular dependence in flat mono- and multifilament bronze-processed Nb3Sn wires, oriented in different directions in a transverse magnetic field, is presented. The influence of various parameters, such as the shape aspect ratio and the heat treatment time and temperature, is examined. It is shown that in monofilament wires, the critical current anisotropy, defined as the ratio of the currents in the parallel and perpendicular orientations of the flat face to the magnetic field, is greater than one at low heat-treatment conditions and changes to less than one with more intensive heat treatment. The multifilament wires behave in the same manner, except that the effects of the gentle and intensive heat treatments are related to the filament size. The mechanical deformation of the niobium core determines the character of the anisotropy at relatively low heat-treatment conditions, while the morphology of the grown Nb3Sn layer is decisive at more intensive heat treatment. The critical current anisotropy of flattened conductors is very important from the theoretical (pinning) as well as from the technical (magnet winding) point of view.

Angular dependence of critical currents in Bi 2Sr 2CaCu 2O 8 thin films predominant role of the transverse magnetic field component

We have studied the critical of c-axis oriented Bi 2Sr 2CaCu 2O 8 thin films measured at various temperatures as a function of magnitude ( H ≤ 20 T) and orientation θ (with respect to the c-axis) of the applied magnetic field. The curves J c (θ) at a giv en field H show a strong maximum when H is parallel to the CuO 2 planes ( θ=90°). For θ≠90°, we show that J c depends o on the component of the magnetic field along the c direction in the whole temperature range. In particular, at 4.2 K, J c( H, θ) behaves as | Hcos θ| -α with 0.44 ≤ α≤0.5. These results agree with the recent scaling theory proposed by Blatter et al. describi the behaviour of anisotropic superconductors for an arbitrary angle between the magnetic field and the anisotropic crystallographic axis.

Angular dependence of critical currents of high temperature superconducting films in high magnetic fields prepared by metalorganic deposition

Critical current measurements have been obtained as a function of angle of the magnetic field to the plane of the thin film metelorganic deposited YBa 2Cu 3O 7- x (YBCO). In the present measurements the current flowed in the a, b plane and was always perpendicular to the applied field. In contrast to the usual observations that show a maximum critical current for H | a, b and a minimum with H | c these new measurements of films with a high critical current density show a secondary maximum with this latter field orientation. Adaptation of a model for angular torque dependence gives a qualitative understanding of the results.

The angular dependence of critical currents in superconductors with long narrow defects

physica status solidi (a)Volume 41, Issue 2 p. K175-K179 Short Note The angular dependence of critical currents in superconductors with long narrow defects S. Takács, S. Takács Electrotechnical Institute, Slovak Academy of Sciences, BratislavaSearch for more papers by this authorA. Pevala, A. Pevala Electrotechnical Institute, Slovak Academy of Sciences, BratislavaSearch for more papers by this author S. Takács, S. Takács Electrotechnical Institute, Slovak Academy of Sciences, BratislavaSearch for more papers by this authorA. Pevala, A. Pevala Electrotechnical Institute, Slovak Academy of Sciences, BratislavaSearch for more papers by this author First published: 16 June 1977 https://doi.org/10.1002/pssa.2210410262Citations: 7AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume41, Issue216 June 1977Pages K175-K179 RelatedInformation

The angular dependence of critical currents in Nb3Sn — Effect of some preparation conditions

By considering some columnar parts in the superconducting grains, we explain some characteristic features in the angular dependence of the critical currents of Nb3Sn tapes, prepared in the presence of additional impurities in the reaction atmosphere of the vapour deposition process. Mainly, the decrease of the critical current in magnetic fields nearly parallel to the tape surface (which appears in the form of a “valley” in the polar diagram of the critical current) can be explained by these considerations. By comparing the theoretical and experimental results, including structural investigations, the most probable shape of the grains is suggested.

The angular dependence of critical currents in Nb3Sn — Effect of some preparation conditions I. Experimental and structural investigations

The results of experimental investigations of the angular dependence of critical currents are presented. The samples studied have been prepared by chemical vapour deposition process in reaction atmosphere of different carrier and doping gases. The results have shown that such conditions influence greatly not only the absolute value of the critical current but also the ratioI c∥/I c⊥ of the critical currents in magnetic fields parallel and perpendicular to the broad face of the tape. The microstructure studies show that the grain shape and size is changed appreciably when various carrier and doping gases are used.

481. Angular dependence of critical currents and transition fields of sputter-deposited superconducting films: Y Saito and T Anayama, J Appl Phys, 44 (11), 1973, 5111–5115.

481. Angular dependence of critical currents and transition fields of sputter-deposited superconducting films: Y Saito and T Anayama, J Appl Phys, 44 (11), 1973, 5111–5115.

Angular dependence of critical currents and transition fields of sputter-deposited superconducting films

Anisotropies in critical currents and transition fields have been measured for sputter-deposited superconducting films. For thicker films, the peak at θ = 90° in the Ic-θ characteristics is strongly marked. As the film thickness decreases, the peak at θ = 90° tends to reduce, and finally disappears in the film thinner than the critical thickness. Furthermore, the transition fields Ht have been found to be anisotropic with respect to the applied field direction θ. The marked peak at θ = 90° in the Ht-θ characteristics is found for films thicker than the critical thickness.