Berlin 2012 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 33: Superconductivity, Measuring Devices, Matter at Low Temperature: Poster Session

TT 33.8: Poster

Wednesday, March 28, 2012, 15:00–19:00, Poster B

Pinning in CaFe_2−xCo_xAs₂ and Ba(Fe_1−xCo_x)₂As₂ single crystals as studied by MWA — •Nadezda Panarina^1,2, Niyaz Beysengulov¹, Yuri Talanov¹, Tatyana Shaposhnikova¹, Evgenia Vavilova¹, Luminita Harnagea², Saicharan Aswartham², Claudia Nacke², Sabine Wurmehl², Christian Hess², Vladislav Kataev², and Bernd Büchner² — ¹Zavoisky Physical-Technical Institute, Kazan, Russia — ²IFW Dresden, Germany

Modulated microwave absorption studies were performed on a series of CaFe_2−xCo_xAs₂ and Ba(Fe_1−xCo_x)₂As₂ single crystals with different Co content. Investigation of pinning features in these samples is of particular interest since there is a significantly wide region of Co concentration, where the superconducting and magnetic orders coexist. Depending on the scale of such electron phase separation, the nonsuperconducting inclusions present in the samples at certain Co concentration may act as additional pinning centers and influence the pinning strength. To estimate the values of the critical current density, an appropriate theoretical model was applied. By analyzing the magnetic field and temperature dependence of the critical current density, we were able to discriminate different types of pinning (small-bundle and large-bundle pinning) in single crystals of CaFe_2−xCo_xAs₂ and Ba(Fe_1−xCo_x)₂As₂. The most effective pinning centers are present in the CaFe_2−xCo_xAs₂ sample at Co concentration corresponding to the boundary of the coexistence of SDW and superconductivity states. This is due to the best correlation of the sizes of additional nonsuperconducting inclusions with the sizes of vortex cores.