Fast recovery of the pristine magnetic and structural phases in superconducting LaFeAsO0.89F0.11 by Mn/Fe substitution

We report an experimental study on the effect of Mn impurities in the optimally doped LaFeAsO0.89F0.11 compound. The results show that a very tiny amount of Mn, of the order of 0.1%, is enough to destroy superconductivity and to recover at low temperatures both the magnetic ground state and the orthorhombic structure of the pristine LaFeAsO parent compound. The results are discussed within a model where electron correlations enhance the Ruderman–Kittel–Kasuya–Yosida interaction among impurities.