Pinning of spiral fluxons by giant screw dislocations in YBa_2Cu_3O_7 single crystals: Josephson analog of the fishtail effect

By using a highly sensitive homemade AC magnetic susceptibility technique, the magnetic flux penetration has been measured in YBa_2Cu_3O_7 single crystals with giant screw dislocations (having the structure of the Archimedean spirals) exhibiting a=3 spiral turnings, the pitch b=18.7 microns and the step height c=1.2nm (the last parameter is responsible for creation of extended weak-link structure around the giant defects). The magnetic field applied parallel to the surface enters winding around the weak-link regions of the screw in the form of the so-called spiral Josephson fluxons characterized by the temperature dependent pitch b_f(T). For a given temperature, a stabilization of the fluxon structure occurs when b_f(T) matches b (meaning an optimal pinning by the screw dislocations) and manifests itself as a pronounced low-field peak in the dependence of the susceptibility on magnetic field (applied normally to the surface) in the form resembling the high-field (Abrikosov) fishtail effect.Comment: see also http://www.jetpletters.ac.ru/ps/1886/article_28701.shtm

AC MAGNETIC RESPONSE IN (Bi-2223+SrCO3)/Ag SUPERCONDUCTING TAPES

AC MAGNETIC RESPONSE IN (Bi-2223+SrCO3)/Ag SUPERCONDUCTING TAPES. A Bi-22231 Ag superconducting tape has been fabricated by means of conventional PIT, followed by eccentric and two axial rolling and heat treatment were introducing an oxide additive (SrCO3) as a barrier. Temperature dependent of AC magnetic susceptibility measurements have been conducted at various external field Ba. The resulted data were analyzed on the basis of strip model using the wills bandfoiitizilation. It was found that the imaginary part ofthe critical current density at O K (Jco) is consistently larger than its real part, but both of them tend to decrease with increasing Ba

MAGNETIC PHASE TRANSITIONS OF T-PHASE Gd2CuO4 SINGLE CRYSTAL

MAGNETIC PHASE TRANSITIONS OF T-PHASE Gd2CuO4 SINGLE CRYSTAL. The magnetic properties of T‘-phase Gd2CuO4 Single crystal grown by the Traveling Solvent Floating Zone (TSFZ) method have been investigated by means of ac-magnetic susceptibility and dc-magnetization measurements. The result of these studies revealed an anomaly in the temperature dependent magnetization at temperature of T = 6.5, 290 and 20 K, associated respectively with the long-range antiferromagnetic ordering of the Gd and Cu ions and Cu- spin reorientation transitions. The complex magnetic structure of this compound shown by the weak ferromagnetic behavior below the copper ordering temperature (TN(Cu) = 290 K) is induced by an effective field due to exchange interactions between the ordered copper moments and the rare-earth ions. These results, together with the previous neutron diffraction measurement, establishes the existence of ferromagnetic Gd layers in the ab-plane which are stacked antiferromagnetically along c-direction, indicating a quasi—two dimensional antiferromagnetic nature of Gd2CuO4

Ac Magnetic Response In (Bi-2223+srco3)/ag Superconducting Tapes

AC MAGNETIC RESPONSE IN (Bi-2223+SrCO3)/Ag SUPERCONDUCTING TAPES. A Bi-22231 Ag superconducting tape has been fabricated by means of conventional PIT, followed by eccentric and two axial rolling and heat treatment were introducing an oxide additive (SrCO3) as a barrier. Temperature dependent of AC magnetic susceptibility measurements have been conducted at various external field Ba. The resulted data were analyzed on the basis of strip model using the wills bandfoiitizilation. It was found that the imaginary part ofthe critical current density at O K (Jco) is consistently larger than its real part, but both of them tend to decrease with increasing Ba

Nd3+ crystal field excitations under magnetic field in La1.65Nd0.35CuO4

We report an infrared crystal field study, under magnetic field, of Nd3+ ions in non-stoichiometric La1.65Nd0.35CuO4. Two sets of crystal field excitations from the ground state multiplet I-4(9/2) to the I-4(11/2) and I-4(13/2) excited multiplets are observed. They correspond to Nd3+ ions located in two different sites. In charge free regions, Nd3+ ion magnetic moments align parallel to the z-axis due to the Nd3+-Cu2+ magnetic interaction. Such interaction is absent in charge rich regions which leaves the corresponding Nd3+ ions in a paramagnetic state. Validity of previous calculations of CF parameters, that predict the Nd3+ electronic levels in the charge free regions as well as magnetic susceptibility anisotropy, is confirmed. (C) 2003 Elsevier B.V. All rights reserved