Chin. Phys. B, 2021, Vol. 30(8): 087402    DOI: 10.1088/1674-1056/ac0695
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# Excess-iron driven spin glass phase in Fe1+yTe1-xSex

Long Tian(田龙)1, Panpan Liu(刘盼盼)1, Tao Hong(洪涛)2, Tilo Seydel3, Xingye Lu(鲁兴业)1,†, Huiqian Luo(罗会仟)4, Shiliang Li(李世亮)4, and Pengcheng Dai(戴鹏程)5,‡
1 Center for Advanced Quantum Studies and Department of Physics, Beijing Normal University, Beijing 100875, China;
2 Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA;
3 Institut Max von Laue-Paul Langevin(ILL), 71 Avenue des Martyrs, CS 20156, 38042 Grenoble Cedex 9, France;
4 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
5 Department of Physics and Astronomy, Rice University, Houston, TX 77005, USA
Abstract  The iron-chalcogenide superconductor FeTe1-xSex displays a variety of exotic features distinct from iron pnictides. Although much effort has been devoted to understanding the interplay between magnetism and superconductivity near x=0.5, the existence of a spin glass phase with short-range magnetic order in the doping range (x～0.1-0.3) has rarely been studied. Here, we use DC/AC magnetization and (quasi) elastic neutron scattering to confirm the spin-glass nature of the short-range magnetic order in a Fe1.07Te0.8Se0.2 sample. The AC-frequency dependent spin-freezing temperature Tf generates a frequency sensitivity ΔTf(ω) /[Tf(ω) Δlog10ω]≈0.028 and the description of the critical slowing down with τ=τ0(Tf / TSG)-zv gives TSG≈22 K and zv≈10, comparable to that of a classical spin-glass system. We have also extended the frequency-dependent Tf to the smaller time scale using energy-resolution-dependent neutron diffraction measurements, in which the TN of the short-range magnetic order increases systematically with increasing energy resolution. By removing the excess iron through annealing in oxygen, the spin-freezing behavior disappears, and bulk superconductivity is realized. Thus, the excess Fe is the driving force for the formation of the spin-glass phase detrimental to bulk superconductivity.
Keywords:  iron chalcogenides      spin glass      neutron scattering
Received:  07 May 2021      Revised:  25 May 2021      Accepted manuscript online:  29 May 2021
 PACS: 74.70.Xa (Pnictides and chalcogenides) 75.30.Gw (Magnetic anisotropy) 78.70.Nx (Neutron inelastic scattering)
Fund: The work at Beijing Normal University is supported by the National Natural Science Foundation of China (Grant Nos. 11734002 and 11922402, X.L.). Work at Rice is supported by the US Department of Energy (DOE), Basic Energy Sciences (BES), under Contract No. DE-SC0012311 (P.D.). A portion of this research used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory.
Corresponding Authors:  Xingye Lu, Pengcheng Dai     E-mail:  luxy@bnu.edu.cn;pdai@rice.edu

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