Upper critical field and superconducting anisotropy of BaFe_2-xRu_xAs₂ (X=0.48 and 0.75) single crystals

The upper critical field (H_c2) was determined by applying a magnetic field along the ab plane and c axis for two single crystals of BaFe_2-xRu_xAs₂ (x=0.48 and 0.75). The anisotropy of the H_c2(0), γ(0)=H_c2^ab(0)/H_c2^c(0), was ~1.6 for x=0.48 and ~2.3 for x=0.75. The angle-dependent resistance measured below T_c allowed perfect scaling features based on anisotropic Ginzburg-Landau theory, leading to consistent anisotropy values. Because only one fitting parameter γ is used in the scaling for each temperature, the validity of the γ value was compared with that determined from γ=H_c2^ab/H_c2^c. The γ obtained at a temperature close to T_c was 3.0 and decreased to 2.0 at low temperatures. Comparing to the anisotropy determined for electron- or hole-doped BaFe₂As₂ using the same method, the present results point to consistent anisotropy in Ru-doped BaFe₂As₂ with other electron- or hole-doped BaFe₂As₂.