Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 8: Superconductivity - Poster Session

TT 8.3: Poster

Monday, March 26, 2007, 14:00–17:45, Poster A

Ru moment in the magnetically ordered superconductor RuSr₂GdCu₂O₈ — •Thomas P. Papageorgiou¹, Eugenio Casini², Yuri Skourski¹, Thomas Herrmannsdörfer¹, Jens Freudenberger³, Hans F. Braun², and Jochen Wosnitza¹ — ¹Hochfeld-Magnetlabor Dresden (HLD), Forschungszentrum Dresden-Rossendorf, D-01314 Dresden, Germany — ²Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany — ³IFW Dresden, Institute for Metallic Materials, D-01171 Dresden, Germany

Magnetization measurements of the superconducting (T_c ≈ 47 K) and magnetically ordered (T_M^Ru ≈ 130 K) RuSr₂GdCu₂O₈ (Ru1212) have been performed in pulsed magnetic fields up to 47 T. The average Ru-moment, determined by using NbSr₂GdCu₂O₈ as reference, is 1.8 µ_B suggesting that the investigated sample is in a mixed valence state containing 87% Ru⁵⁺ (2 µ_B) and 13% Ru⁴⁺ (0.9 µ_B). This ratio is consistent with an underdoped nature of the superconducting state with a hole concentration in the CuO₂ plane of p ≈ 0.065. It is suggested that the magnetic structure of Ru1212 consists of a main antiferromagnetic phase formed by Ru⁵⁺ions interrupted by ferromagnetic stripes, where double exchange between Ru⁵⁺ and Ru⁴⁺ ions takes place. Different Ru⁵⁺/Ru⁴⁺ ratios, due to different preparation conditions, could explain some of the diverse superconducting and magnetic properties reported in the literature for Ru1212.