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Single-ion properties of the Seff = 1 2 XY antiferromagnetic pyrochlores NaA Co2F7 (A = Ca2+, Sr2+)

Author(s): Ross, KA; Brown, JM; Cava, Robert J; Krizan, Jason W; Nagler, SE; et al

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Abstract: 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 [K. A. Ross et al., Phys. Rev. B 93, 014433 (2016)]. 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. 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.
Publication Date: Apr-2017
Electronic Publication Date: 13-Apr-2017
Citation: Ross, KA, Brown, JM, Cava, RJ, Krizan, JW, Nagler, SE, Rodriguez-Rivera, JA, Stone, MB. (2017). Single-ion properties of the Seff = 1 2 XY antiferromagnetic pyrochlores NaA Co2F7 (A = Ca2+, Sr2+). Physical Review B, 95 (14), 10.1103/PhysRevB.95.144414
DOI: doi:10.1103/PhysRevB.95.144414
ISSN: 2469-9950
EISSN: 2469-9969
Pages: 144414-1 - 144414-11
Type of Material: Journal Article
Journal/Proceeding Title: Physical Review B
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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