Fish-tail Effect and Irreversibility Field of (Cu,C)Ba$_{2}$Ca$_{3}$Cu$_{4}$O$_{x}$-(LiF)$_{y}$ superconductor

TL;DR

This study demonstrates how adding LiF and AgO to a specific superconductor enhances its fish-tail effect and irreversibility field by optimizing doping levels, leading to improved magnetic properties at high temperatures.

Contribution

It introduces a method to control doping in (Cu,C)Ba2Ca3Cu4O10+d superconductors using LiF and AgO, resulting in improved magnetic irreversibility and fish-tail effects.

Findings

Optimal doping with y=0.1 LiF and z=0.73 AgO enhances Jc and H_irr.

The best sample maintains single-phase Cu,C-1234 composition.

Enhanced irreversibility properties are observed above a temperature T*.

Abstract

Addition of (LiF)$_{y<0.15}$, and of proper amount of (AgO)$_{z=0.45-0.8}$ as oxidizing agent, to (Cu,C)Ba$_{2}$Ca$_{3}$Cu$_{4}$O$_{10+d}$ superconductor is useful to control and shift the doping characteristics (hole density and distribution, and level of disorder) into the region where the irreversible properties, i.e. fish-tail effect (FTE) and irreversibility field H$_{irr}$, are improved. Among notable effects are the development of the second magnetization peak with a higher amplitude J$_{c}$, max and the enhancement of H$_{irr}$ at high temperatures, above a certain value T* which depends on both y$_{LiF}$ and z$_{AgO}$. The best results are obtained for the sample with y$_{LiF}$=0.1 and z$_{AgO}$=0.73. This sample preserves its single phase Cu,C-1234 composition. The influence on the FTE and H$_{irr}$ of the interplay between doping characteristics, controlled by LiF and AgO content, is discussed.