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Title: Observation of the magnetic C 4 phase in Ca 1 - x Na x Fe 2 As 2 and its universality in the hole-doped 122 superconductors

Since its discovery in 2014, the magnetic tetragonal C 4 phase has been identified in a growing number of hole-doped 122 Fe-based superconducting compounds. Exhibiting a unique double-Q magnetic structure and a strong competition with both superconducting and magnetic order parameters, the C 4 phase and the conditions of its formation are of significant interest to understanding the fundamental mechanisms in these materials. Particularly, separating the importance of direct changes to the relative size of hole and electron pockets at the Fermi surface (achieved via charge doping) from the role of structural changes due to differences of ionic radii of dopants is useful to determine the underlying parameter which causes the C 4 instability. Here, we report the discovery of the C 4 phase in a fourth member of the hole-doped 122 materials Ca 1-xNa xFe 2As 2(0.20 ≤ x ≤ 0.50) as determined from neutron and x-ray powder diffraction studies. The maximum of the C 4 dome is observed at x = 0.44 with a reentrant temperature T r = 52 K and an extent of Δx ~ 0.07 in composition. It is observed that for a range of compositions within the C 4 dome (0.40 ≤ x ≤more » 0.42), there is a second reentrance (Tr 2 < Tr) where the antiferromagnetic C 2 phase is recovered—a feature previously only seen in Ba 1-xK xFe 2As 2. A phase diagram is presented for Ca 1-xNa xFe 2As 2 and compared to the other Na-doped 122's—A 1-xNa xFe 2As 2 with A = Ba, Sr, and Ca. Lastly, the structural parameters for these three systems are compared and the importance of the “chemical pressure” due to changing the A-site ion (A = Ba, Sr, Ca) is discussed.« less
 [1] ;  [2] ;  [2] ;  [2] ;  [3] ;  [2] ;  [2] ;  [4] ;  [2] ;  [2] ;  [3]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Northern Illinois Univ., DeKalb, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
  2. Argonne National Lab. (ANL), Argonne, IL (United States)
  3. Northern Illinois Univ., DeKalb, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
  4. Argonne National Lab. (ANL), Argonne, IL (United States); Northwestern Univ., Evanston, IL (United States)
Publication Date:
Grant/Contract Number:
AC02-06CH11357; AC05-00OR22725
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 95; Journal Issue: 6; Journal ID: ISSN 2469-9950
American Physical Society (APS)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Scientific User Facilities Division; Materials Sciences and Engineering Division
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1344007; OSTI ID: 1376534