title: Unconventional temperature enhanced magnetism in Fe1.1Te.
abstract: Our inelastic neutron scattering study of spin excitations in iron telluride reveals remarkable thermal evolution of the collective magnetism. In the temperature range relevant for the superconductivity in FeTe(1-x)Se(x) materials, where the local-moment behavior is dominated by liquidlike correlations of emergent spin plaquettes, we observe unusual, marked increase of magnetic fluctuations upon heating. The effective spin per Fe at T ≈ 10  K, in the phase with weak antiferromagnetic order, corresponds to S ≈ 1, consistent with the recent analyses that emphasize importance of Hund's coupling [K. Haule and G. Kotliar, New J. Phys. 11, 025021 (2009).]. However, it grows to S ≈ 3/2 in the high-T disordered phase, suggestive of the Kondo-type behavior, where local magnetic moments are entangled with the itinerant electrons.
authors.affiliation: CMPMSD, Brookhaven National Laboratory, Upton, New York 11973, USA. zaliznyak@bnl.gov
authors.forename: Igor A
authors.initials: IA
authors.lastname: Zaliznyak
authors.forename: Zhijun
authors.initials: Z
authors.lastname: Xu
authors.forename: John M
authors.initials: JM
authors.lastname: Tranquada
authors.forename: Genda
authors.initials: G
authors.lastname: Gu
authors.forename: Alexei M
authors.initials: AM
authors.lastname: Tsvelik
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Stone