Europhys. Lett.
Volume 73, Number 4, February 2006
Page(s) 587 - 593
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 11 January 2006
Europhys. Lett., 73 (4), pp. 587-593 (2006)
DOI: 10.1209/epl/i2005-10423-5

Observation of enhanced fluctuation diamagnetism in lanthanum superconductors with dilute magnetic impurities

F. Soto, L. Cabo, J. Mosqueira, M. V. Ramallo, J. A. Veira and F. Vidal

Laboratorio de Baixas Temperaturas e Superconductividade, Departamento de Física da Materia Condensada, Universidade de Santiago de Compostela - E-15782 Spain

received 4 November 2005; accepted 7 December 2005
published online 11 January 2006

The fluctuation-induced diamagnetism $\Delta M$, associated with the presence of precursor Cooper pairs in the normal state, has been measured in lanthanum with dilute magnetic (Pr) and nonmagnetic (Lu) impurities. It is found that while for pure La and La-Lu alloys $\Delta M$ agrees, as expected, with the predictions based on the conventional Gaussian-Ginzburg-Landau approach, it is much larger for La-Pr alloys (around a factor 5 for La-2 at.%Pr). These results suggest the existence of an indirect contribution to $\Delta M$ arising from the interaction between fluctuating Cooper pairs and magnetic impurities.

74.25.Ha - Magnetic properties.
74.40.+k - Fluctuations (noise, chaos, nonequilibrium superconductivity, localization, etc.).

© EDP Sciences 2006