Mn DOPED (Cuo.5 Tlo.5) Ba2Ca2Cu3O10.8 superconductors

Abstract

Mn-doped 05Tl ,Ba2(Ca,.yM ny)Cu301O~ (y=O, 0.15, 0.25, 035, 0.5, 0,75, 1.0) samples synthesized at room temperature employing solid state reaction method and their superconducting properties are studied. In these experiments, it is expected that the multiple oxidation states of doped Mn (more than +2) at the Ca site would enhance the inter-plane coupling and enhance the magnitude the superconductivity. Contrary to our expectation, the T,(R =O) and magnitude of superconductivity are systematically suppressed with increased Mn-doping. The suppression of superconductivity is explained in terms of decreased density of mobile carriers associated with possible localizalion of the carriers at the Mn sites. It is most likely that the suppressed density of the mobile carriers in the conducting CU02 plane may increase the anti-ferromagnetic alignment of the spins of CU atoms which decrease the magnitude of superconductivity. The doping of Mn at the intrinsic sites of the unit cell is verified by Fourier Transform Infrared Spectroscopy (FTIR) measurements. From the FTIR absorption measurements it observed that the CU02 planar oxygen mode is hardened whereas the apical oxygen mode of CU(1)-OA-Cu(2) is softened with increased Mn·doping. The optimization of the carriers in the conducting CU02 planes is brought about by carrying out self·doping experiments in oxygen atmosphere. After-post annealing in oxygen, the CU(1)-OA-Cu(2) mode is softened with increased Mn dop!ng, which lead us to believe that doped Mn atoms alter the charge state of Cu atoms and hence possibly the spin alignment of Cu atoms in the CU02 planes.