We study the structural and magnetic orders in electron-doped BaFe2-xNixAs2 by high-resolution synchrotron X-ray and neutron scatterings. Upon Ni-doping x, the nearly simultaneous tetragonal-to-orthorhombic structural T_s and antiferromagnetic (T_N) phase transitions in BaFe2As2 are gradually suppressed and separated, resulting in T_s>T_N with increasing x as was previously observed. However, the temperature separation between T_s and T_N decreases with increasing x for x> 0.065,tendingtowardsaquantumbi−criticalpointnearoptimalsuperconductivityatx=0.1.Thezero−temperaturetransitionispreemptedbytheformationofasecondaryincommensuratemagneticphaseintheregion0.088<x<0.104,resultinginafinitevalueofTN≈Tc+10 K above the superconducting dome around x≈0.1. Our results imply an avoided quantum critical point, which is expected to strongly influence the properties of both the normal and superconducting states.
@article{arxiv.1306.4757,
title = {Avoided quantum criticality and magnetoelastic coupling in BaFe$_{2-x}$Ni$_{x}$As$_{2}$},
author = {Xingye Lu and H. Gretarsson and Rui Zhang and Xuerong Liu and Huiqian Luo and Wei Tian and Mark Laver and Z. Yamani and Young-June Kim and A. H. Nevidomskyy and Qimiao Si and Pengcheng Dai},
journal= {arXiv preprint arXiv:1306.4757},
year = {2013}
}