Electrical resistivity and magnetization study on LaFe2As2, La0.8Ba0.2Fe2As2, and La1-xBaxPt0.1Fe1.9As2 (x=0, 0.05, 0.2, 0.4, and 0.6) superconducting compounds

Abstract

We report the magnetic properties of LaFe2As2, La0.8Ba0.2Fe2As2, and La1-xBaxPt0.1Fe1.9As2 (0 <= x <= 0.6) compounds prepared by solid-state reaction in a wide temperature range of 5-300 K in a field up to 9 T. All as-prepared samples act as superconducting magnets at low temperatures under normal atmospheric pressure. The magnetic state of LaFe2As2 has been studied in detail in a temperature range of 5-200 K for the fields in between H = +/- 1 T. We conclude that the samples are made up of a large number of smaller and similar magnetic domains developed by the thermal agitation under the internal magnetic field during the cooling process. Considering LaFe2As2 as a parent compound, it is assumed that substituting of Ba2+ to the site La3+ results in hole doping similar to K doping in Ba1-xKxFe2As2. We have investigated the magnetic properties of La1-xBax Pt0.1Fe1.9As2. The paramagnetic contribution to the magnetization is determined by fitting the M (H, 5 K) curve using the Langevin function for each sample. Then, from the paramagnetic subtracted M-H curves, the critical current density, J(c), and normalized pinning force F-p/F-p,F-max as a function of the applied field is obtained. Moreover, the normalized pinning force density, F-p/F-p,F-max, curves versus h = H/H-irr (H-irr is the irreversibility field) were scaled using the Dew-Hughes model. Hence, the nature of the flux-pinning centers is revealed. Based on the results obtained from these analyses, we claim that the superconductivity in all as-prepared samples occurs on the domain boundary with the filamentary character and bulk superconductivity inside the domains.