A combination of x-ray diffraction, magnetization, and 75As nuclear magnetic resonance (NMR) experiments were performed on single-crystal EuFe1.9Co0.1As2. The strength of the hyperfine interaction between the 75As nuclei and the Eu^(2+) 4f states suggests a strong coupling between the Eu^(2+) moments and the Fe1.9Co0.1As2 layers. Such a strong interlayer coupling may be due to an indirect exchange interaction between the localized Eu^(2+) 4f moments, mediated by the Fe 3d conduction electrons. Magnetic susceptibility as well as 75As-NMR measurements reveal a decrease of the SDW transition temperature to T_SDW = 120 K as a result of Co doping. A change of the slope in the temperature dependence of the NMR frequency of the 75As lower-satellite line was observed at 225 K. At the same temperature also a change of the satellite line shape was found. These changes of the NMR spectra may be caused by the formation of a nematic phase below 225 K in EuFe1.9Co0.1As2.
@article{arxiv.1010.5948,
title = {Strong coupling between Eu2+ spins and Fe2As2 layers in EuFe1.9Co0.1As2 observed with NMR},
author = {Z. Guguchia and J. Roos and A. Shengelaya and S. Katrych and Z. Bukowski and S. Weyeneth and F. Murányi and S. Strässle and A. Maisuradze and J. Karpinski and H. Keller},
journal= {arXiv preprint arXiv:1010.5948},
year = {2015}
}