Single-Ion Properties of the Seff = 1/2 XY Antiferromagnetic Pyrochlores NaA'Co2F7 (A' = Ca2+, Sr2+)

Published

April 13, 2017

Author(s)

K. A. Ross, J. M. Brown, R. J. Cava, J. W. Krizan, S. E. Nagler, Jose Rodriguez Rivera, M. B. Stone

Abstract

The antiferromagnetic pyrochlore material NaCaCo₂F₇ is a thermal spin liquid over a broad temperature range (approximately equal} 140 K down to T_F = 2.4K), in which magnetic correlations between Co²⁺ dipole moments explore a continuous manifold of antiferromagnetic XY states. ^1^ 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 than 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 (g_xy/g_z3). 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 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.

Citation

Physical Review B

Volume

95

Issue

14

Pub Type

Journals

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Keywords

Neutron Scattering, Magnetism, Spin liquids

Citation

Ross, K. , Brown, J. , Cava, R. , Krizan, J. , Nagler, S. , Rodriguez Rivera, J. and Stone, M. (2017), Single-Ion Properties of the S_eff = 1/2 XY Antiferromagnetic Pyrochlores NaA'Co₂F₇ (A' = Ca²⁺, Sr²⁺), Physical Review B, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=922702 (Accessed July 17, 2024)