Abstract
The RuSr <sub>2</sub> GdCu <sub>2</sub> O <sub>8</sub> Ru-1212 cuprate is a weak-ferromagnetic superconductor with a magnetic ordering of Ru moments at TN(Ru) 131 K, a superconducting transition in the CuO <sub>2</sub> layers at T <sub>c</sub> 56 K, and a low temperature Gd antiferromagnetic ordering at T <sub>N</sub> (Gd) 2.5 K. The c-axis aligned powder can be achieved at room temperature using the field-rotation method where the tetragonal c-axis is perpendicular to the aligned magnetic field B <sub>a</sub> and along the rotation axis. The anisotropic temperature dependence of magnetic susceptibility for the aligned powder down to 2 K indicates weak anisotropy with X <sub>c</sub> > Xab at room temperature due to strong anisotropic Gd contribution and X <sub>c</sub> < Xab below 185 K where strong Ru anisotropic short-range exchange interaction overtakes the Gd contribution. Anisotropic diamagnetic superconducting intragrain shielding signal of aligned microcrystalline 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 μm), long penetration depth (λ <sub>ab</sub> ∼ 0.6 μm, λ <sub>c</sub> ∼ 2 μm) and the two-dimensional (2D) character of CuO <sub>2</sub> layers. © 2009 IOP Publishing Ltd.