Nd1+x Ba2-x Cu3O7-d Single Crystals Flux-grown at Various Undercoolings and Their Superconducting Properties

Mechanisms, features, and properties of strong flux pinning in superconducting 123 materials are reviewed. These include pinning by nonsuperconducting particles of 211 or 422 phase, regions with lower critical temperature (T c ) such as a region where Ba sites are substituted for with light rare-earth elements and an oxygen-deficient region, and radiation-induced columnar defects. In particular, the pinning by lower-T c regions which seem to be associated with the well-known pronounced peak effect are focused upon. It is speculated that these regions work as strong repulsive pinning centres resulting from the kinetic energy of the order parameter under a significant proximity effect. This pinning mechanism is different from the usual attractive condensation energy interaction which occurs in 211 or 422 particles. A discussion will be given on the mechanism which brings about the peak effect. General guiding principles for the improvement of the flux pinning property will also be discussed.

Section: Pinning By Defects Other Than Columnar Defectssupporting

confidence: 94%

“…The flux pinning by Nd-422 particles in Nd-123 superconductor was investigated by Higuchi et al [6]. They measured the critical current density for a melt-processed sample with Nd-422 particles and a Nd-123 single crystal.…”

Section: Pinning By Defects Other Than Columnar Defectsmentioning

confidence: 99%

Flux pinning in superconducting 123 materials

Matsushita

2000

“…Several different Nd-based superconductors were chosen for this investigation. Single crystals of NdBa 2 Cu 3 O 7−δ (NdBCO) were grown by a flux growth method in controlled oxygen atmosphere as described in [12]. Both crystals are twinned.…”

Section: Methodsmentioning

confidence: 99%

Superconducting transitions of Nd-based 123 superconductors in fields up to 7 T

Koblischka

Muralidhar

Higuchi

et al. 1999

Superconducting transitions were measured in field-cooled cooling and field-cooled warming modes in external magnetic fields ranging between 1 mT and 7 T on various Nd-based 123 superconductors (NdBa 2 Cu 3 O 7−δ single crystals and melt-processed samples, and melt-textured ternary compounds). Most of the Nd-based superconductors investigated exhibit a two-step transition when being cooled or warmed in fields larger than 4 T. We ascribe this effect to the presence of an Nd-rich phase providing a spatial scatter of the transition temperature, T c , throughout the sample.

“…The field distribution was scanned by a Hall probe at a distance of 5 mm from the face of the superconductor; the apparatus is described in [5]. The description of the sample preparation is given in detail elsewhere (NEG [7,8], and NdBCO single crystals [9,10]).…”

Section: Samples and Experimental Methodsmentioning

confidence: 99%

Field-cooled magnetization measurements of Nd-123 bulk superconductors

Koblischka

Johansen

Murakami

2000

The field-cooled (FC) magnetization M is measured as a function of the applied external field, H a , for various bulk, Nd-based 123 superconductors which exhibit different magnetization-field characteristics (i.e. with and without secondary peak effect). We find that the FC magnetization data reproduce directly the M(H a ) behaviour measured after zero-field cooling. Based on the critical state model, we derive expressions for the field-cooled magnetization, and show that a large M(0) is essential to achieve large trapped fields in superconducting permanent magnets.