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.
Ross, Kathryn A., Brown, J. M., Cava, R. J., Krizan, J. W., Nagler, Stephen E., Rodriguez-Rivera, J. A., & Stone, Matthew B. (2017). Single-ion properties of the <math><msub><mi>S</mi><mi>eff</mi></msub></math> = <math><mfrac><mn>1</mn><mn>2</mn></mfrac></math> XY antiferromagnetic pyrochlores <math><mrow><mi>Na</mi><msup><mi>A</mi><mo>'</mo></msup><msub><mi>Co</mi><mn>2</mn></msub><msub><mi mathvariant='normal'>F</mi><mn>7</mn></msub></mrow></math> ( <math><mrow><msup><mi>A</mi><mo>'</mo></msup><mo>=</mo><msup><mrow><mi>Ca</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></mrow><mo>,</mo><mo> </mo><msup><mrow><mi>Sr</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></math> ). Physical Review B, 95(14). https://doi.org/10.1103/PhysRevB.95.144414
Ross, Kathryn A., Brown, J. M., Cava, R. J., et al., "Single-ion properties of the <math><msub><mi>S</mi><mi>eff</mi></msub></math> = <math><mfrac><mn>1</mn><mn>2</mn></mfrac></math> XY antiferromagnetic pyrochlores <math><mrow><mi>Na</mi><msup><mi>A</mi><mo>'</mo></msup><msub><mi>Co</mi><mn>2</mn></msub><msub><mi mathvariant='normal'>F</mi><mn>7</mn></msub></mrow></math> ( <math><mrow><msup><mi>A</mi><mo>'</mo></msup><mo>=</mo><msup><mrow><mi>Ca</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></mrow><mo>,</mo><mo> </mo><msup><mrow><mi>Sr</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></math> )," Physical Review B 95, no. 14 (2017), https://doi.org/10.1103/PhysRevB.95.144414
@article{osti_1471947,
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.},
title = {Single-ion properties of the <math><msub><mi>S</mi><mi>eff</mi></msub></math> = <math><mfrac><mn>1</mn><mn>2</mn></mfrac></math> XY antiferromagnetic pyrochlores <math><mrow><mi>Na</mi><msup><mi>A</mi><mo>'</mo></msup><msub><mi>Co</mi><mn>2</mn></msub><msub><mi mathvariant='normal'>F</mi><mn>7</mn></msub></mrow></math> ( <math><mrow><msup><mi>A</mi><mo>'</mo></msup><mo>=</mo><msup><mrow><mi>Ca</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></mrow><mo>,</mo><mo> </mo><msup><mrow><mi>Sr</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></math> )},
annote = {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},
url = {https://www.osti.gov/biblio/1471947},
journal = {Physical Review B},
issn = {ISSN PRBMDO},
number = {14},
volume = {95},
place = {United States},
publisher = {American Physical Society (APS)},
year = {2017},
month = {04}}
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 764https://doi.org/10.1016/j.nima.2014.07.029