Magnetic field dependence of the precursor diamagnetism in La superconductors with magnetic Pr impurities

TL;DR

This study investigates how magnetic impurities influence the fluctuation diamagnetism in La superconductors, revealing a linear increase with impurity concentration and proposing a Ginzburg-Landau model to explain these effects.

Contribution

It provides experimental evidence and a phenomenological model describing the magnetic field dependence of fluctuation diamagnetism in La superconductors with magnetic impurities.

Findings

FD increases linearly with impurity concentration

Magnetic field reduces the fluctuation diamagnetism

Proposed Ginzburg-Landau model explains the impurity effects

Abstract

The interplay between fluctuating Cooper pairs and magnetic impurities in conventional BCS low-Tc superconductors has been studied through measurements of the magnetic field dependence of the fluctuation diamagnetism (FD) above Tc in lanthanum with praseodymium impurities. These measurements provide a crucial confirmation of our previous observation [Europhys. Lett. 73, 587 (2006)] that in the dilute impurity regime the FD increases almost linearly with the concentration of magnetic impurities. This striking effect is attributed to a variation due to the presence of the fluctuating Cooper pairs of the coupling between magnetic impurities. To describe these results at a phenomenological level, we propose a Gaussian Ginzburg-Landau model for the FD which includes an indirect contribution proportional to both the impurities concentration and the Cooper pairs density. Our approach is able to explain simultaneously the FD increase due to magnetic impurities and its decrease with the application of large magnetic fields.