Effects of Pt and La doping on the superconductivity of CaFe2As2: Kondo effects

We report the magnetic properties of CaFe2As2, CaFe1·9Pt0·1As2, and Ca0·9La0·1Fe1·9Pt0·1As2 compounds in a wide temperature range of 5–300 K in the field up to 9 T. We have observed a well-defined anomaly in the resistivity around 165 K, which manifests clearly a well-known first order magneto structural phase transition from paramagnetic-tetragonal (T) state to antiferromagnetic orthorhombic (Ort) one. Pt doped and Pt and La co-doped CaFe2As2 samples exhibit a Kondo lattice behavior. The critical current density, Jc, and normalized pinning force Fp/Fp,max as a function of the applied field are obtained. Moreover, the normalized pinning force density, Fp/Fp,max curves versus h = H/Hirr were scaled using the Dew-Hughes model. Hence, the natures of the flux-pinning centers for these samples are revealed. Based on the results obtained from these analyses, we claim that the superconductivity in as-prepared CaFe2As2 occurs on the grain-boundary with the filamentary character.