Volume 87, Number 3, August 2009
Article Number 37001
Number of page(s) 6
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
Published online 18 August 2009
EPL, 87 (2009) 37001
DOI: 10.1209/0295-5075/87/37001

Homogeneous vs. inhomogeneous coexistence of magnetic order and superconductivity probed by NMR in Co- and K-doped iron pnictides

M.-H. Julien1, H. Mayaffre1, M. Horvatić2, C. Berthier2, X. D. Zhang3, W. Wu3, G. F. Chen3, N. L. Wang3 and J. L. Luo3

1   Laboratoire de Spectrométrie Physique, UMR5588 CNRS and Université J. Fourier Grenoble, 38402 Saint Martin d'Hères, France, EU
2   Laboratoire National des Champs Magnétiques Intenses, UPR 3228 CNRS 25 avenue des martyrs, BP 166, 38042 Grenoble Cedex 9, France, EU
3   Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Science - P.O. Box 603, Beijing 100190, China

received 19 June 2009; accepted in final form 23 July 2009; published August 2009
published online 18 August 2009

In Ba(Fe0.95Co0.05)2As2 all of the 75As NMR intensity at the paramagnetic resonance position vanishes abruptly below $T^{{\rm onset}}_{{\rm SDW}}$ = 56 K, indicating that magnetic (spin-density wave) order is present in all of the sample volume, despite bulk superconductivity below Tc = 15 K. The two phases thus coexist homogeneously at the microscopic scale. In Ba0.6K0.4Fe2As2, on the other hand, the signal loss below $T^{{\rm onset}}_{{\rm SDW}}$ $\simeq$ 75 K is not complete, revealing that magnetic order is bound to finite-size areas of the sample, while the remaining NMR signal shows a clear superconducting response below Tc = 37 K. Thus, the two phases are not homogeneously mixed, at least for this potassium concentration. For both samples, spatial electronic and/or magnetic inhomogeneity is shown to characterize the NMR properties in the normal state.

74.25.Ha - Magnetic properties.
75.30.Fv - Spin-density waves.
76.60.-k - Nuclear magnetic resonance and relaxation.

© EPLA 2009