We use inelastic neutron scattering to study temperature dependence of the paramagnetic spin excitations in iron pnictide BaFe2As2 throughout the Brillouin zone. In contrast to a conventional local moment Heisenberg system, where paramagnetic spin excitations are expected to have a Lorentzian function centered at zero energy transfer, the high-energy (ℏω>100 meV) paramagnetic spin excitations in BaFe2As2 exhibit spin-wave-like features up to at least 290 K (T=2.1TN). Furthermore, we find that the sizes of the fluctuating magnetic moments <m2>≈3.6μB2 per Fe are essentially temperature independent from the AF ordered state at 0.05TN to 2.1TN, which differs considerably from the temperature dependent fluctuating moment observed in the iron chalcogenide Fe1.1Te [I. A. Zaliznyak {\it et al.}, Phys. Rev. Lett. {\bf 107}, 216403 (2011).]. These results suggest unconventional magnetism and strong electron correlation effects in BaFe2As2.
@article{arxiv.1209.6271,
title = {Temperature dependence of the paramagnetic spin excitations in BaFe$_2$As$_2$},
author = {Leland W. Harriger and Mengshu Liu and Huiqian Luo and R. A. Ewings and C. D. Frost and T. G. Perring and Pengcheng Dai},
journal= {arXiv preprint arXiv:1209.6271},
year = {2012}
}