Eur. Phys. J. B (2013) 86: 458
https://doi.org/10.1140/epjb/e2013-40483-6

Regular Article

⁷⁵As NMR local probe study of magnetism in (Eu_1−xK_x)Fe₂As₂

¹ Department of Physics, Indian Institute of Technology Bombay, Powai, 400076 Mumbai, India
² Department of Physics, Indian Institute of Technology Kanpur, 208016 Kanpur, India

^a Present address: IFW Dresden, 01171 Dresden, Germany e-mail: tusdey@gmail.com
^b Present address: Max-Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany

Received: 13 May 2013
Received in final form: 5 August 2013
Published online: 4 November 2013

Abstract

⁷⁵As NMR measurements were performed as a function of temperature and doping in Eu_1−xK_xFe₂As₂ (x = 0.5,0.7) samples. The large Eu²⁺ moments and their fluctuations are found to dominate the ⁷⁵As NMR properties. The ⁷⁵As nuclei close to the Eu²⁺ moments likely have a very short spin-spin relaxation time (T₂) and are wiped out of our measurement window. The ⁷⁵As nuclei relatively far from Eu²⁺ moments are probed in this study. Increasing the Eu content progressively decreases the signal intensity with no signal found for the full-Eu sample (x = 0). The large ⁷⁵As NMR linewidth arises from an inhomogeneous magnetic environment around them. The spin lattice relaxation rate (1/T₁) for x = 0.5 and 0.7 samples is nearly independent of temperature above 100 K and results from a dipolar coupling to paramagnetic fluctuations of the Eu²⁺ moments. The behavior of 1/T₁ at lower temperatures has contributions from the antiferromagnetic fluctuations of the Eu²⁺ moments as also the fluctuations intrinsic to the FeAs planes and from superconductivity.