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Title: Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca ( Fe 1 x Co x ) 2 As 2

Abstract

Results of inelastic neutron scattering measurements are reported for two annealed compositions of Ca(Fe1–xCox)2As2, x = 0.026 and 0.030, which possess stripe-type antiferromagnetically ordered and superconducting ground states, respectively. In the AFM ground state, well-defined and gapped spin waves are observed for x = 0.026, similar to the parent CaFe2As2 compound. We conclude that the well-defined spin waves are likely to be present for all x corresponding to the AFM state. This behavior is in contrast to the smooth evolution to overdamped spin dynamics observed in Ba(Fe1–xCox)2As2, wherein the crossover corresponds to microscopically coexisting AFM order and SC at low temperature. The smooth evolution is likely absent in Ca(Fe1–xCox)2As2 due to the mutual exclusion of AFM ordered and SC states. Overdamped spin dynamics characterize paramagnetism of the x = 0.030 sample and high-temperature x = 0.026 sample. A sizable loss of magnetic intensity is observed over a wide energy range upon cooling the x = 0.030 sample, at temperatures just above and within the superconducting phase. This phenomenon is unique amongst the iron-based superconductors and is consistent with a temperature-dependent reduction in the fluctuating moment. In conclusion, one possible scenario ascribes this loss of moment to a sensitivity to themore » c-axis lattice parameter in proximity to the nonmagnetic collapsed tetragonal phase and another scenario ascribes the loss to a formation of a pseudogap.« less

Authors:
 [1];  [1];  [1];  [1];  [2];  [1];  [1];  [1];  [1];  [1]
  1. Ames Lab. and Iowa State Univ., Ames, IA (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Ames Lab., Ames, IA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1439423
Alternate Identifier(s):
OSTI ID: 1439367
Report Number(s):
IS-J-9669
Journal ID: ISSN 2469-9950; PRBMDO; TRN: US1900607
Grant/Contract Number:  
AC02-07CH11358
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 97; Journal Issue: 17; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Sapkota, A., Das, P., Bohmer, A. E., Ueland, B. G., Abernathy, D. L., Bud'ko, S. L., Canfield, P. C., Kreyssig, A., Goldman, A. I., and McQueeney, R. J.. Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca(Fe1–xCox)2As2. United States: N. p., 2018. Web. https://doi.org/10.1103/PhysRevB.97.174519.
Sapkota, A., Das, P., Bohmer, A. E., Ueland, B. G., Abernathy, D. L., Bud'ko, S. L., Canfield, P. C., Kreyssig, A., Goldman, A. I., & McQueeney, R. J.. Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca(Fe1–xCox)2As2. United States. https://doi.org/10.1103/PhysRevB.97.174519
Sapkota, A., Das, P., Bohmer, A. E., Ueland, B. G., Abernathy, D. L., Bud'ko, S. L., Canfield, P. C., Kreyssig, A., Goldman, A. I., and McQueeney, R. J.. Tue . "Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca(Fe1–xCox)2As2". United States. https://doi.org/10.1103/PhysRevB.97.174519. https://www.osti.gov/servlets/purl/1439423.
@article{osti_1439423,
title = {Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca(Fe1–xCox)2As2},
author = {Sapkota, A. and Das, P. and Bohmer, A. E. and Ueland, B. G. and Abernathy, D. L. and Bud'ko, S. L. and Canfield, P. C. and Kreyssig, A. and Goldman, A. I. and McQueeney, R. J.},
abstractNote = {Results of inelastic neutron scattering measurements are reported for two annealed compositions of Ca(Fe1–xCox)2As2, x = 0.026 and 0.030, which possess stripe-type antiferromagnetically ordered and superconducting ground states, respectively. In the AFM ground state, well-defined and gapped spin waves are observed for x = 0.026, similar to the parent CaFe2As2 compound. We conclude that the well-defined spin waves are likely to be present for all x corresponding to the AFM state. This behavior is in contrast to the smooth evolution to overdamped spin dynamics observed in Ba(Fe1–xCox)2As2, wherein the crossover corresponds to microscopically coexisting AFM order and SC at low temperature. The smooth evolution is likely absent in Ca(Fe1–xCox)2As2 due to the mutual exclusion of AFM ordered and SC states. Overdamped spin dynamics characterize paramagnetism of the x = 0.030 sample and high-temperature x = 0.026 sample. A sizable loss of magnetic intensity is observed over a wide energy range upon cooling the x = 0.030 sample, at temperatures just above and within the superconducting phase. This phenomenon is unique amongst the iron-based superconductors and is consistent with a temperature-dependent reduction in the fluctuating moment. In conclusion, one possible scenario ascribes this loss of moment to a sensitivity to the c-axis lattice parameter in proximity to the nonmagnetic collapsed tetragonal phase and another scenario ascribes the loss to a formation of a pseudogap.},
doi = {10.1103/PhysRevB.97.174519},
journal = {Physical Review B},
number = 17,
volume = 97,
place = {United States},
year = {2018},
month = {5}
}

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Cited by: 2 works
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Figures / Tables:

FIG. 1 FIG. 1: (a) Phase diagram of Ca(Fe1-xCo$x$)2As2 annealed at 400°C showing the magnetostructural transition from the high-temperature tetragonal (T) and paramagnetic (PM) to the orthorhombic (O) and antiferromagnetic (AFM) phase, as well as the superconducting (SC) phase. Stars indicate the positions at which our INS measurements were performed. (b),(c) Magnetizationmore » data illustrating the T-PM to O-AFM transition at $T$S,N for $x$ = 0.026 (purple circles) and the superconducting transition at $T$$c$ for $x$ = 0.030 (green circles). (d) Temperature dependence of the $c$ lattice parameter for $x$ = 0.026 (purple line) and 0.030 (green line). The $c$ lattice parameters for the $x$ = 0.026 and 0.030 samples at 300 K were obtained from the center of the (0, 0, 8) Bragg peak, measured with neutron diffraction. The temperature dependence plots in (d) were made by normalizing dilatometry data for $x$ = 0.027 and 0.029 given in Ref. 27 to the value of $c$ at $T$ = 300 K for $x$ = 0.026 and 0.030, respectively. An abrupt increase in $c$ is seen for $x$ = 0.026 at $T$S,N.« less

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