Session J35: Focus Session: Iron Pnictides and Other Novel Superconductors VIII: Magnetism (Experiment)

11:15 AM–2:03 PM, Tuesday, March 17, 2009
Room: 405

Sponsoring Unit: DMP
Chair: Jeff Lynn, National Institute of Standards and Technology

Abstract ID: BAPS.2009.MAR.J35.5

Abstract: J35.00005 : The crystalline electric field as a probe for long range antiferromagnetic order and superconductivity in CeFeAsO$_{1-x}$F$_x$

12:03 PM–12:15 PM

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Authors:

  Songxue Chi
    (University of Tennessee, Knoxville)

  Devashibhai Adroja
    (ISIS Facility, Rutherford Appleton Laboratory)

  Titiana Guidi
    (ISIS Facility, Rutherford Appleton Laboratory,)

  Robert Bewley
    (ISIS Facility, Rutherford Appleton Laboratory,)

  Shiliang Li
    (University of Tennessee, Knoxville)

  Jun Zhao
    (University of Tennessee, Knoxville)

  Jeffrey Lynn
    (NIST Center for Neutron Research)

  Craig Brown
    (NIST Center for Neutron Research)

  Yiming Qiu
    (NIST Center for Neutron Research)

  Gen Fu Chen
    (Institute of Physics, Chinese Academy of Sciences)

  Jian Lin Luo
    (Institute of Physics, Chinese Academy of Sciences)

  Nan Lin Wang
    (Institute of Physics, Chinese Academy of Sciences)

  Pengcheng Dai
    (University of Tennessee, Knoxville)

We use inelastic neutron scattering to study the crystalline electric field (CEF) excitations of Ce$^{3+}$ in CeFeAsO$_{1-x}$F$_{x}$($x=0,0.16$). For nonsuperconducting CeFeAsO, the Ce CEF levels have three magnetic doublets in the paramagnetic state, but these doublets split into six singlets when Fe ions order antiferromagnetically. For superconducting CeFeAsO$_{0.84}$F$_{0.16}$ ($T_c=41$ K), where the static AF order is suppressed, the Ce CEF levels have three magnetic doublets at $\hbar\omega=0,18.7,58.4$ meV at all temperatures. Careful measurements of the intrinsic linewidth $\Gamma$ and the peak position of the 18.7 meV mode reveal clear anomaly at $T_c$, consistent with a strong enhancement of local magnetic susceptibility $\chi^{\prime\prime}(\hbar\omega)$ below $T_c$. These results suggest that CEF excitations in the rare-earth oxypnictides can be used as a probe of spin dynamics in the nearby FeAs planes.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.MAR.J35.5