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Title: Single-ion properties of the S eff = 1 2 XY antiferromagnetic pyrochlores Na A ' Co 2 F 7 ( A ' = Ca 2 + ,   Sr 2 + )

Abstract

The antiferromagnetic pyrochlore material NaCaCo 2F 7 is a thermal spin liquid over a broad temperature range (≈140 K down to T F=2.4 K), in which magnetic correlations between Co 2+ dipole moments explore a continuous manifold of antiferromagnetic XY states. The thermal spin liquid is interrupted by spin freezing at a temperature that is ~2% of the mean-field interaction strength, leading to short-range static XY clusters with distinctive relaxation dynamics. Here we report the low-energy inelastic neutron scattering response from the related compound NaSrCo 2F 7, confirming that it hosts the same static and dynamic spin correlations as NaCaCo 2F 7. We then present the single-ion levels of Co 2+ in these materials as measured by inelastic neutron scattering. An intermediate spin-orbit coupling model applied to an ensemble of trigonally distorted octahedral crystal fields accounts for the observed transitions. The single-ion ground state of Co 2+ is a Kramers doublet with a strongly XY-like g tensor ( gxy/gz~3). The local disorder inherent from the mixed pyrochlore A sites (Na +/Ca 2+ and Na +/Sr 2+) is evident in these measurements as exaggerated broadening of some of the levels. A simple model that reproduces the salient features of the single-ionmore » spectrum produces approximately 8.4% and 4.1% variation in the z and xy components of the g tensor, respectively. In conclusion, this study confirms that an S eff = 1/2 model with XY antiferromagnetic exchange and weak exchange disorder serves as a basic starting point in understanding the low-temperature magnetic behavior of these strongly frustrated magnets.« less

Authors:
 [1];  [2];  [3];  [3]; ORCiD logo [4];  [5]; ORCiD logo [4]
  1. Colorado State Univ., Fort Collins, CO (United States); Canadian Institute for Advanced Research, Toronto, ON (Canada)
  2. Colorado State Univ., Fort Collins, CO (United States)
  3. Princeton Univ., Princeton, NJ (United States)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  5. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); Univ. of Maryland, College Park, MD (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1471947
Alternate Identifier(s):
OSTI ID: 1351673
Grant/Contract Number:  
AC05-00OR22725; FG02-08ER46544
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 95; Journal Issue: 14; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE

Citation Formats

Ross, Kathryn A., Brown, J. M., Cava, R. J., Krizan, J. W., Nagler, Stephen E., Rodriguez-Rivera, J. A., and Stone, Matthew B.. Single-ion properties of the Seff = 12 XY antiferromagnetic pyrochlores NaA'Co2F7 ( A'=Ca2+, Sr2+ ). United States: N. p., 2017. Web. doi:10.1103/PhysRevB.95.144414.
Ross, Kathryn A., Brown, J. M., Cava, R. J., Krizan, J. W., Nagler, Stephen E., Rodriguez-Rivera, J. A., & Stone, Matthew B.. Single-ion properties of the Seff = 12 XY antiferromagnetic pyrochlores NaA'Co2F7 ( A'=Ca2+, Sr2+ ). United States. doi:10.1103/PhysRevB.95.144414.
Ross, Kathryn A., Brown, J. M., Cava, R. J., Krizan, J. W., Nagler, Stephen E., Rodriguez-Rivera, J. A., and Stone, Matthew B.. Thu . "Single-ion properties of the Seff = 12 XY antiferromagnetic pyrochlores NaA'Co2F7 ( A'=Ca2+, Sr2+ )". United States. doi:10.1103/PhysRevB.95.144414. https://www.osti.gov/servlets/purl/1471947.
@article{osti_1471947,
title = {Single-ion properties of the Seff = 12 XY antiferromagnetic pyrochlores NaA'Co2F7 ( A'=Ca2+, Sr2+ )},
author = {Ross, Kathryn A. and Brown, J. M. and Cava, R. J. and Krizan, J. W. and Nagler, Stephen E. and Rodriguez-Rivera, J. A. and Stone, Matthew B.},
abstractNote = {The antiferromagnetic pyrochlore material NaCaCo2F7 is a thermal spin liquid over a broad temperature range (≈140 K down to TF=2.4 K), in which magnetic correlations between Co2+ dipole moments explore a continuous manifold of antiferromagnetic XY states. The thermal spin liquid is interrupted by spin freezing at a temperature that is ~2% of the mean-field interaction strength, leading to short-range static XY clusters with distinctive relaxation dynamics. Here we report the low-energy inelastic neutron scattering response from the related compound NaSrCo2F7, confirming that it hosts the same static and dynamic spin correlations as NaCaCo2F7. We then present the single-ion levels of Co2+ in these materials as measured by inelastic neutron scattering. An intermediate spin-orbit coupling model applied to an ensemble of trigonally distorted octahedral crystal fields accounts for the observed transitions. The single-ion ground state of Co2+ is a Kramers doublet with a strongly XY-like g tensor (gxy/gz~3). The local disorder inherent from the mixed pyrochlore A sites (Na+/Ca2+ and Na+/Sr2+) is evident in these measurements as exaggerated broadening of some of the levels. A simple model that reproduces the salient features of the single-ion spectrum produces approximately 8.4% and 4.1% variation in the z and xy components of the g tensor, respectively. In conclusion, this study confirms that an Seff = 1/2 model with XY antiferromagnetic exchange and weak exchange disorder serves as a basic starting point in understanding the low-temperature magnetic behavior of these strongly frustrated magnets.},
doi = {10.1103/PhysRevB.95.144414},
journal = {Physical Review B},
number = 14,
volume = 95,
place = {United States},
year = {Thu Apr 13 00:00:00 EDT 2017},
month = {Thu Apr 13 00:00:00 EDT 2017}
}

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Works referenced in this record:

Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides
journal, September 1976