[WBP2] Bulk, Assembled Conductors, AC Loss

[WBP2-25] Biaxial orientation degrees of (Y_1-xEr_x)Ba₂Cu₃O_y powders aligned under the oscillation type modulated rotating magnetic field

*Shigeru Horii¹, Daisuke Notsu², Toshiya Doi² (1. Kyoto University of Advanced Science (Japan), 2. Kyoto University (Japan))

Keywords:

Magnetic alignment,Modulated rotation magnetic field,REBa2Cu3O7

REBa₂Cu₃O₇ superconductors with T_c ∼ 90 K require formation of biaxial grain orientation for practical application due to the weak link at grain boundary. The typical technique for achieving biaxial alignment and densification is epitaxial growth technique, such as melt-solidification with seed crystal and thin film growth on highly oriented substrate. On the other hand, our group focuses on the biaxial magnetic alignment by modulated rotating magnetic field, MRF as a triaxial alignment technique of materials and is currently investigating a material production process based on MRF. Magnetic alignment using MRF offers several advantages: it operates at room temperature, does not require a highly oriented substrate, and enables triaxial grain alignment. These intriguing features of MRF lead to possibilities of production of biaxially oriented RE123 thick films with hundreds micron levels and higher critical currents. Various types of MRF have been reported and the static field, SF, and rotating field, RF, components are included in any type of MRF. The most typical MRF in our group is the intermittent type MRF. However, in the present study, our group focuses on another type of MRF, the oscillation, OS, type MRF. Figure 1a shows a schematic of the OS type MRF and its advantages are that the OS process includes both SF and RF components simultaneously and these can be systematically controlled by the oscillation angle, θ. For θ <90 deg, the first easy, second easy and hard axes are aligned normal to the a, b and g planes, respectively. We examined the biaxial orientation degrees of twinned Y_1-xEr_x123 powder samples aligned in epoxy resin under the OS type MRF with controlling q and magnetic field, B_a, and clarified the roles of SF and RF. Incidentally, Y123 shows χ_c >χ_a>χ_b as magnetic susceptibility, χ, relationshp and lower magnetic anisotropy, Δχ, whereas Er123 shows χ_b>χ_a>χ_c and higher Δχ. Figure 1b shows relationship between the biaxial orientation degree, F, and θ for the magnetically aligned Y_1-xEr_x123 powder samples with MRF of B_a = 5 T. Incidentally, due to the different directions on the first easy axis in Y_1-xEr_x123, the a plane was used for the 103 pole figure measurement in the Y123 and the g plane was used in Y_1-xEr_x123 with x = 0.5 and 1. The F values of Y123 showed ~10% for θ <20 deg, and F was increased monotonically with θ for θ >30 deg. However, the F values of Y_1-xEr_x123 with x = 0.5 and 1 showed F >30% in a whole θ region with 1.8 deg< θ <90 deg. Theoretically, the increase in θ leads to the increase in the RF component and the decrease in the SF component. Fig. 1b demonstrates that magnetic anisotropies of Y_1-xEr_x123 with x = 0.5 and 1 are obviously higher than that of Y123. Furthermore, the improvement of the biaxial orientation degrees in Y123 under 5 T of OS-MRF can be explained in terms of the provision of the θ-dependent RF component of magnetic alignment energy. In the presentation, the results of the F-θ curves under different B_a for x= 0, 0.5 and 1 are shown. Relationships between F and θ in Y_1-xEr_x123 will be theoretically discussed from the viewpoints of SF and RF components of magnetic alignment energies.