Structural and spin-glass properties of single crystal J_eff = 1/2 pyrochlore antiferromagnet NaCdCo₂F₇ : correlating T_fwith magnetic-bond-disorder

Author(s)

Andrej Kancko, Gerald Giester, Ross H. Colman

Abstract

Weak bond disorder disrupts the expected spin-liquid ground-state of the ideal S = 1/2 Heisenberg pyrochlore antiferromagnet. Here we introduce a single crystal study of the structural and magnetic properties of the bond-disordered pyrochlore NaCdCo₂F₇. The magnetic susceptibility appears isotropic, with a large negative Curie-Weiss temperature (theta_CW =-108(1) K), however no magnetic order is observed on cooling until a spin-glass transition at T_f = 4.0 K. AC-susceptibility measurements show a frequency-dependent shift of the associated cusp in chi at T_f, that can be fitted well by the empirical Vogel-Fulcher law. The magnetic moment of eff = 5.4(1) _B/Co²⁺ indicates a significant orbital contribution and heat capacity measurements show that down to 1.8 K, well below T_f, only S_mag ~23 Rln(2) of the magnetic entropy is recovered, suggestive of residual continued dynamics. Structural and magnetism comparisons are made with the other known members of the NaACo₂F₇ family (A = Ca²⁺, Sr²⁺), confirming the expected relationship between spin-glass freezing temperature, and extent of magnetic bond disorder brought about by the size mismatch between A-site ions.

Organisation(s)

Department of Mineralogy and Crystallography

External organisation(s)

Charles University Prague

Publication date

02-2023

Austrian Fields of Science 2012

103015 Condensed matter

Portal url

https://ucrisportal.univie.ac.at/en/publications/2a989866-08de-4a68-a73c-3e6a4ce3773b