Texture effect on vortex‐state TF‐μ⁺SR in Bi‐2223 high‐T_C materials

Abstract

The influence of texture in Bi‐2223 ingots on the temperature dependence of the μ⁺ spin relaxation rate has been investigated. Texture was induced during cold‐isostatic‐pressing by applying an additional uniaxial load which tends to align single grain c axes along the stress direction, \widehatz. Small plates were cut with faces either \Vert or \perp \widehatz and μSRwas measured in a 15 mT transverse field (TF) during cooling from room temperature to 6 K. While for highly‐textured material, low‐temperature limits are substantially smaller than expected, the large shift (55%) observed when switching from \widehatz\perp TF to \widehatz\,\Vert TF clearly indicates that anisotropy has developed. Relaxation rates for the weakly‐textured sample lie in between. To a lesser extent, sintering also enhanced the low‐temperature relaxation, but did not affect T_C significantly. All samples showed a weak onset of depolarization between 60 K and 90 K, most likely due to the presence of a Bi‐2212 impurity phase. This impurity phase might cause the transition‐temperature smearing in the 100–110 K range in the weakly textured (and less compacted) material. Thus the sharpness of the relaxation drop might be relevant for assessment of material quality and be used as a criterion in the improvement of the production process.