Columnar defects acting as passive internal field detectors

Abstract

We have studied the angular dependence of the irreversible magnetization of several YBa 2 Cu 3 O 7 and 2H-NbSe 2 single crystals with columnar defects tilted off the c axis. At high magnetic fields, the irreversible magnetization M i (⌰) exhibits a well-known maximum when the applied field is parallel to the tracks. As the field is decreased below Hϳ0.02H c2 , the peak shifts away from the tracks' direction toward either the c axis or the ab planes. We demonstrate that this shift results from the misalignment between the external and internal field directions due to the competition between anisotropy and geometry effects.

Critical Current Densities of MOCVD Tapes for Different Current Directions

“…This corresponds to a reduced field of , which is very similar to the value of found in [15]. The agreement is remarkable, given that the experiment in the latter study was performed on single crystals, rather than thin films, using magnetic measurements, rather than a transport technique.…”

“…This behavior has again been reported previously [4], [5], [14] and was explained by an offset between the direction of the applied field and the magnetic flux density in the sample, given by the orientation of the vortices [15]. The maxima move from the -planes to the defect planes and then further towards the -axis, which corresponds to the "anisotropy-dominated" case described in [15].…”

“…This behavior has again been reported previously [4], [5], [14] and was explained by an offset between the direction of the applied field and the magnetic flux density in the sample, given by the orientation of the vortices [15]. The maxima move from the -planes to the defect planes and then further towards the -axis, which corresponds to the "anisotropy-dominated" case described in [15]. Note that the peak found at film normal at intermediate fields discussed above moves in the opposite direction, confirming that in one sample the "anisotropy-dominated" and the "geometry-dominated" situation can be observed at the same time [14].…”

Glassy Dynamics in a heavy ion irradiated NbSe2 crystal

“…Pinning from CDs is directional; that is, at high enough fields, pinning is strongest, therefore J c is highest, when the field is parallel to the CDs 5 . Despite the strong pinning capacity of CDs, YBCO crystals containing parallel CDs are known to demonstrate extremely high creep rates under certain measurement conditions.…”

Influence of random point defects introduced by proton irradiation on critical current density and vortex dynamics of Ba(Fe0.925Co0.075)Haberkorn1, Maiorov2, Usov3 et al. 2012Phys. Rev. B7015772View full textAdd to dashboardCite

“…29 In all cases B -vanishes approximately as 1/H at high fields (the free energy minimizes for B H), while for the particular parameters of our crystal (which is in the "geometry dominated case" in the classification of Ref. 26) in the low H limit B →0 (the system minimizes the free energy by reducing the length of the vortices).…”