Progressive slowing down of spin fluctuations in underdoped LaFeAsO1xFx

F. Hammerath, U. Gräfe, T. Kühne, H. Kühne, P. L. Kuhns, A. P. Reyes, G. Lang, S. Wurmehl, B. Büchner, P. Carretta, and H.-J. Grafe
Phys. Rev. B 88, 104503 – Published 4 September 2013

Abstract

The evolution of low-energy spin dynamics in the iron-based superconductor LaFeAsO1xFx was studied over a broad doping, temperature, and magnetic field range (x= 0–0.15, T 480 K, μ0H 30 T) by means of 75As nuclear magnetic resonance. An enhanced spin-lattice relaxation rate divided by temperature (T1T)1 in underdoped superconducting samples (x= 0.045, 0.05, and 0.075) suggests the presence of antiferromagnetic spin fluctuations, which are strongly reduced in optimally doped (x=0.10) and completely absent in overdoped (x=0.15) samples. In contrast to previous analysis, Curie-Weiss fits are shown to be insufficient to describe the data over the whole temperature range. Instead, a Bloembergen-Purcell-Pound (BPP) model is used to describe the occurrence of a peak in (T1T)1 clearly above the superconducting transition, reflecting a progressive slowing down of the spin fluctuations down to the superconducting phase transition.

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  • Received 11 July 2013

DOI:https://doi.org/10.1103/PhysRevB.88.104503

©2013 American Physical Society

Authors & Affiliations

F. Hammerath1,2,*, U. Gräfe2, T. Kühne2, H. Kühne3, P. L. Kuhns3, A. P. Reyes3, G. Lang2,4, S. Wurmehl2,5, B. Büchner2,5, P. Carretta1, and H.-J. Grafe2

  • 1Dipartimento di Fisica and Unità CNISM di Pavia, I-27100 Pavia, Italy
  • 2IFW Dresden, Institute for Solid State Research, PF 270116, 01171 Dresden, Germany
  • 3National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
  • 4LPEM UMR8213, CNRS–ESPCI ParisTech–UPMC, 75005 Paris, France
  • 5Institute for Solid State Physics, Dresden Technical University, TU-Dresden, 01062 Dresden, Germany

  • *franziska.hammerath@unipv.it

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Vol. 88, Iss. 10 — 1 September 2013

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