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Mukuda H.,Osaka University | Mukuda H.,TRIP Transformative Research Project on Iron Pnictides | Terasaki N.,Osaka University | Yashima M.,Osaka University | And 15 more authors.
Journal of Physics: Conference Series | Year: 2010

We report systematic 57Fe-NMR study on an underdoped sample (Tc = 20 K), an optimally doped sample (Tc = 28 K), and an overdoped sample (Tc = 22 K) of oxygen-deficient iron (Fe)-based oxypnictide superconductor LaFeAsO1-y. The 57Fe-1/T 1T in the normal state decreases significantly upon cooling regardless of an electron-doping level, revealing that 1/T1T is not always enhanced by antiferromagnetic fluctuations close to an antiferromagnetic phase in the underdoped superconducting sample. This contrasts with the behavior in hole-doped Ba0.6K0.4Fe2As 2(Tc = 38 K), which exhibits a significant increase in 1/T1T upon cooling. We suggest that the crucial difference between the normal-state properties of LaFeAsO1-yand Ba0.6K 0.4Fe2As2 originates from the fact that the relevant Fermi surface topologies are differently modified depending on whether electrons or holes are doped into the FeAs layers. © 2010 IOP Publishing Ltd. Source

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