Compositional dependence of low energy spin fluctuations in Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$

ORAL

Abstract

The low energy magnetic fluctuation spectrum of Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ samples in the range $x=(0.014,0.055)$ were studied in their antiferromagnetic ordered states using inelastic neutron scattering. The parent compound BaFe$_2$As$_2$ exhibits gapped spin-wave excitations at $\mathbf{Q}_{\mathrm{AFM}} = (1, 0, 1)$ with two gap energies [corresponding to in-Fe-plane and out-of-Fe-plane transverse excitations of the ordered moment]. Substitution of Co for Fe via doping acts to increase Landau damping without significantly modifying the parent compound spin-gap structure. For small amounts of Co the two-gap structure is resolvable in our measurements. For larger Co-doping the damping increases sufficiently to obscure the parent compound gap structure and the measured $\mathbf{Q}_{\mathrm{AFM}}$ excitation spectra is best described by a diffusive model. Interestingly, the change in excitation character corresponds in composition with the appearance of superconductivity in Ba(Fe$_{1-x}$Co$_{x}$)$_2$As; these two effects may very well be related.

*The work at the Ames Laboratory was supported by US DOE, Office of Basic Energy Sciences, DMSE, contract DE-AC02-07CH11358.

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Authors

  • Gregory Tucker

    • Ames Laboratory and Department of Physics \& Astronomy, Iowa State University, Ames, IA 50011

  • D.K. Pratt

    • Ames Laboratory and Department of Physics \& Astronomy, Iowa State University, Ames, IA 50011

  • A. Thaler

    • Ames Laboratory and Department of Physics \& Astronomy, Iowa State University, Ames, IA 50011

  • N. Ni

    • Ames Laboratory and Department of Physics \& Astronomy, Iowa State University, Ames, IA 50011

  • K. Marty

    • Quantum Condensed Matter Division, Neutron Science Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831

  • A.D. Christianson

    • Quantum Condensed Matter Division, Neutron Science Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831

  • M.D. Lumsden

    • Quantum Condensed Matter Division, Neutron Science Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831

  • S.L. Bud'ko

    • Ames Laboratory and Department of Physics \& Astronomy, Iowa State University, Ames, IA 50011

  • P.C. Canfield

    • Ames Laboratory and Department of Physics \& Astronomy, Iowa State University, Ames, IA 50011

  • A. Kreyssig

    • Ames Laboratory and Department of Physics \& Astronomy, Iowa State University, Ames, IA 50011

  • A.I. Goldman

    • Ames Laboratory and Department of Physics \& Astronomy, Iowa State University, Ames, IA 50011

  • R.J. McQueeney

    • Ames Laboratory and Department of Physics \& Astronomy, Iowa State University, Ames, IA 50011