Biaxial magnetic alignment in twinned REBa2Cu3Oysuperconductors

S Horii, T Nishioka, I Arimoto, S Fujioka, T Doi
2016 Superconductors Science and Technology  
Biaxial magnetic alignment of REBa 2 Cu 3 O y (RE123, RE=Y, Nd, Sm, Dy, and Er) superconductor powders containing twin microstructures was demonstrated. Appropriate choice of RE effectively improved the degrees of in-plane and c-axis orientation in RE123 powder samples aligned under modulated rotating magnetic fields at room temperature. From the relationship between the magnetic field strength and the degrees of orientation, it is concluded that heavy RE ions induced the improvement of the
more » ... lane magnetic anisotropies in RE123 grains with twin microstructures. 1.Introduction The rare-earth (RE)-based cuprate superconductor REBa 2 Cu 3 O y (RE123) shows critical temperature (T c ) with approximately 90 K, and its T c is higher than the boiling temperature of liquid nitrogen (77.3 K). RE123 possesses a layered crystal structure stacked along the c-axis, which is including superconducting CuO 2 planes spread along the ab-plane and a one-dimensional CuO chain running parallel to the b-axis. Due to low electromagnetic anisotropy of carriers induced by the metallic CuO chain as a blocking layer of RE123 with y ~ 7, RE123 shows an intrinsically higher irreversibility field (H irr ) at 77 K as compared with those for other cuprate superconductors [1]. One recognizes that RE123 compounds are practical superconductors not only for electric power cables but also for magnet application. However, due to the short coherence length and d-wave symmetry of the Cooper pair in cuprate superconductors, the intergrain critical current density (intergrain J c ) of the c-axis-oriented RE123 bicrystal decreases significantly with an increase in the misorientation angle at the grain boundary[2]. Therefore, a biaxial grain orientation is required in addition to the formation of a densified microstructure to achieve practical in-field and self-field J c properties. Epitaxial growth methods, such as thin film growth on single-crystalline substrates [3] and melt-solidification using seed crystals [4], have been adopted to obtain biaxially oriented RE123 materials thus far. Recently, a biaxial grain-orientation technique using a frequency-modulated rotating magnetic field, which is a technique for simultaneously aligning both the easy and hard axes of magnetization using a modulated rotation magnetic field (MRF), has been developed [5] . In principle, this technique is extensively applied for various polycrystalline functional materials that have triaxial magnetic anisotropy with sufficiently large differences in magnetic susceptibilities (χ) along crystallographic axes. Due to magnetic field energy proportional to the square of H, number of substances appropriate for the magnetic alignment are expected to increase remarkably by the use of 10-tesla-class high field magnets. At the current stage, cryogen-free superconducting magnets [6] which can generate ~10 T have been available commercially. In practice, the biaxial orientation of a twin-free Y 2 Ba 4 Cu 7 O y (Y247: y~15) superconductor [7-9], which is an analog compound of RE123, with high degrees of in-plane and c-axis orientations below 2°, has been achieved in epoxy resin at room temperature under an MRF of 12 T [8, 9] as a proof of principle. Our group has also reported the biaxial orientation in epoxy resin at room temperature for twin-free REBa 2 Cu 4 O 8 (RE124) superconductors [10] and the triaxial magnetic anisotropies depending on the type of RE ions for RE124 [10] and
doi:10.1088/0953-2048/29/12/125007 fatcat:ybw4o2am4bcm5kfjvismwskiam