Structural and spin-glass properties of single crystal J(eff)=1/2 pyrochlore antiferromagnet NaCdCo2F7: correlating T-f with magnetic-bond-disorder
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-beta, that can be fitted well by the empirical Vogel-Fulcher law.
The magnetic moment of mu(eff) = 5.4(1) mu(B)/Co2+ indicates a significant orbital contribution and heat capacity measurements show that down to 1.8 K, well below T-beta only S-mag similar to 2/3 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 NaA''Co2F7 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.