Anisotropic microcrystalline powder alignment of the weak-ferromagnetic superconductor system RuSr₂RCu₂O₈ (R Pr, Nd, Sm, Eu, Gd, Gd_0.5Dy_0.5)

The powder alignment method is used to investigate the anisotropic physical properties of the weak-ferromagnetic superconductor system RuSr ₂RCu₂O₈ (R Pr, Nd, Sm, Eu, Gd, Gd _0.5Dy_0.5). Due to weak magnetic anisotropy of this tetragonal system, partially c-axis aligned microcrystalline powder (diameter ∼ 1-10 μm) 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 B_a 0.9 T and parallel to the rotation axis. For smaller rare earth compound R Gd_0.5Dy_0.5, powder alignment can be achieved using the simple field powder alignment method where c-axis is partially aligned along the aligned magnetic field. No powder alignment can be achieved for larger rare earths R Pr, Nd or Sm due to the lack of magnetic anisotropy in these compounds. The mechanism of powder alignment at room temperature using the spin-orbital-related anisotropic paramagnetic susceptibility and the low temperature anisotropic physical properties of RuSr₂EuCu₂O₈ is discussed.