Antiferromagnetic spin correlations and pseudogaplike behavior in Ca(Fe1xCox)2As2 studied by As75 nuclear magnetic resonance and anisotropic resistivity

J. Cui, B. Roy, M. A. Tanatar, S. Ran, S. L. Bud'ko, R. Prozorov, P. C. Canfield, and Y. Furukawa
Phys. Rev. B 92, 184504 – Published 6 November 2015

Abstract

We report As75 nuclear magnetic resonance (NMR) measurements of single-crystalline Ca(Fe1xCox)2As2 (x=0.023, 0.028, 0.033, and 0.059) annealed at 350C for 7 days. From the observation of a characteristic shape of As75 NMR spectra in the stripe-type antiferromagnetic (AFM) state, as in the case of x=0 (TN=170 K), clear evidence for the commensurate AFM phase transition with the concomitant structural phase transition is observed in x=0.023 (TN=106 K) and x=0.028 (TN=53 K). Through the temperature dependence of the Knight shifts and the nuclear spin lattice relaxation rates (1/T1), although stripe-type AFM spin fluctuations are realized in the paramagnetic state as in the case of other iron pnictide superconductors, we found a gradual decrease of the AFM spin fluctuations below a crossover temperature T* that was nearly independent of Co-substitution concentration, and it is attributed to a pseudogaplike behavior in the spin excitation spectra of these systems. The T* feature finds correlation with features in the temperature-dependent interplane resistivity, ρc(T), but not with the in-plane resistivity ρa(T). The temperature evolution of anisotropic stripe-type AFM spin fluctuations is tracked in the paramagnetic and pseudogap phases by the 1/T1 data measured under magnetic fields parallel and perpendicular to the c axis. Based on our NMR data, we have added a pseudogaplike phase to the magnetic and electronic phase diagram of Ca(Fe1xCox)2As2.

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  • Received 1 August 2015
  • Revised 21 October 2015

DOI:https://doi.org/10.1103/PhysRevB.92.184504

©2015 American Physical Society

Authors & Affiliations

J. Cui1,2, B. Roy1,3, M. A. Tanatar1,3, S. Ran1,3, S. L. Bud'ko1,3, R. Prozorov1,3, P. C. Canfield1,3, and Y. Furukawa1,3

  • 1Ames Laboratory, U.S. DOE, Ames, Iowa 50011, USA
  • 2Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
  • 3Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA

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Vol. 92, Iss. 18 — 1 November 2015

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