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Title: The effects of post-growth annealing on the structural and magnetic properties of BaFe 2As 2

Here, we investigate the effects of post-growth annealing on the structural and magnetic properties of BaFe 2As 2. Magnetic susceptibility measurements, which exhibit a signal corresponding to the magnetic phase transition, and high-resolution x-ray diffraction measurements, which directly probe the structural order parameter, show that annealing causes the ordering temperatures of both the phase transitions to increase, sharpen and converge. In the as grown sample, our measurements show two distinct transitions corresponding to structural and magnetic ordering, which are separated in temperature by approximately 1 K. After 46 days (d) of annealing at 700 °C, the two become concurrent in temperature. These measurements demonstrate that the structural phase transition is second-order like when the magnetic and structural phase transitions are separated in temperature, and first-order like when the two phase transition temperatures coincide. This observation indicates that annealing causes the system to cross a hitherto undiscovered tricritical point. In addition, x-ray diffraction measurements show that the c-axis lattice parameter increases with annealing up to 30 d, but remains constant for longer annealing times. Comparisons of BaFe 2As 2 to SrFe 2As 2 are made when possible.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Univ. of California, Berkeley, CA (United States); European Synchrotron Radiation Facility, Grenoble Cedex (France)
  2. Univ. of California, Berkeley, CA (United States)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  5. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Journal of Physics. Condensed Matter
Additional Journal Information:
Journal Volume: 28; Journal Issue: 11; Related Information: © 2016 IOP Publishing Ltd.; Journal ID: ISSN 0953-8984
Publisher:
IOP Publishing
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Superconductivity; Iron-pnictides; Structural phase transition
OSTI Identifier:
1466692
Alternate Identifier(s):
OSTI ID: 1238403

Forrest, T. R., Valdivia, P. N., Rotundu, C. R., Bourret-Courchesne, E., and Birgeneau, R. J.. The effects of post-growth annealing on the structural and magnetic properties of BaFe2As2. United States: N. p., Web. doi:10.1088/0953-8984/28/11/115702.
Forrest, T. R., Valdivia, P. N., Rotundu, C. R., Bourret-Courchesne, E., & Birgeneau, R. J.. The effects of post-growth annealing on the structural and magnetic properties of BaFe2As2. United States. doi:10.1088/0953-8984/28/11/115702.
Forrest, T. R., Valdivia, P. N., Rotundu, C. R., Bourret-Courchesne, E., and Birgeneau, R. J.. 2016. "The effects of post-growth annealing on the structural and magnetic properties of BaFe2As2". United States. doi:10.1088/0953-8984/28/11/115702. https://www.osti.gov/servlets/purl/1466692.
@article{osti_1466692,
title = {The effects of post-growth annealing on the structural and magnetic properties of BaFe2As2},
author = {Forrest, T. R. and Valdivia, P. N. and Rotundu, C. R. and Bourret-Courchesne, E. and Birgeneau, R. J.},
abstractNote = {Here, we investigate the effects of post-growth annealing on the structural and magnetic properties of BaFe2As2. Magnetic susceptibility measurements, which exhibit a signal corresponding to the magnetic phase transition, and high-resolution x-ray diffraction measurements, which directly probe the structural order parameter, show that annealing causes the ordering temperatures of both the phase transitions to increase, sharpen and converge. In the as grown sample, our measurements show two distinct transitions corresponding to structural and magnetic ordering, which are separated in temperature by approximately 1 K. After 46 days (d) of annealing at 700 °C, the two become concurrent in temperature. These measurements demonstrate that the structural phase transition is second-order like when the magnetic and structural phase transitions are separated in temperature, and first-order like when the two phase transition temperatures coincide. This observation indicates that annealing causes the system to cross a hitherto undiscovered tricritical point. In addition, x-ray diffraction measurements show that the c-axis lattice parameter increases with annealing up to 30 d, but remains constant for longer annealing times. Comparisons of BaFe2As2 to SrFe2As2 are made when possible.},
doi = {10.1088/0953-8984/28/11/115702},
journal = {Journal of Physics. Condensed Matter},
number = 11,
volume = 28,
place = {United States},
year = {2016},
month = {2}
}