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arXiv · 0811.3457

Anisotropic magnetic and superconducting properties of aligned weak-ferromagnetic superconductor RuSr$_2$RCu$_2$O$_8$ (R = rare earths)

B. C. Chang·C. H. Hsu·M. F. Tai·H. C. Ku·Y. Y. Hsu
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Abstract

The powder alignment method is used to investigate the anisotropic physical properties of the weak-ferromagnetic superconductor system RuSr2RCu2O8 (R = Pr, Nd, Sm, Eu, Gd, Gd0.5Dy0.5). The RuSr2GdCu2O8 cuprate is a weak-ferromagnetic superconductor with a magnetic ordering of Ru moments at TN(Ru) = 131 K, a superconducting transition in the CuO2 layers at Tc = 56 K, and a low temperature Gd antiferromagnetic ordering at TN(Gd) = 2.5 K. Due to weak magnetic anisotropy of this tetragonal system, highly c-axis aligned microcrystalline powder (diameter ~ 1-10 $μ$m) in epoxy can be obtained only for R = Eu and Gd through the field-rotation powder alignment method where c-axis is perpendicular to the aligned magnetic field Ba = 0.9 T and parallel to the rotation axis. For smaller rare earth compound R = Gd0.5Dy0.5, powder alignment can be achieved using the simple field powder alignment method where c-axis is partially aligned along the aligned magnetic field. The anisotropic temperature dependence of magnetic susceptibility for the c-axis aligned powders exhibit weak anisotropy with $χ_{c} > χ_{ab}$ at room temperature due to anisotropic rare earth, Eu and Gd, contribution and crossover to $χ_{c} < χ_{ab}$ below 190 K where strong Ru anisotropic short-range exchange interaction overtakes the rare earth contribution. Anisotropic diamagnetic superconducting intragrain shielding signal of aligned microcrystalline RuSr2GdCu2O8 powder-in-epoxy below vortex lattice melting temperature at 39 K in 1-G field is much weaker than the intergrain polycrystalline bulk sample signal due to the small grain size (d ~ 1-10 $μ$m), long penetration depth ($λ_{ab}$ ~ 0.55 $μ$m, $λ_{c}$ ~ 0.66 $μ$m) and the two-dimensional (2D) character of CuO2 layers.

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B. C. Chang, C. H. Hsu, M. F. Tai, H. C. Ku, Y. Y. Hsu. 2008-11-21. Anisotropic magnetic and superconducting properties of aligned weak-ferromagnetic superconductor RuSr$_2$RCu$_2$O$_8$ (R = rare earths). https://arxiv.org/abs/0811.3457

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