Misjudging frustrations in spin liquids from oversimplified use of Curie-Weiss law

- Curie-Weiss fitting may give erroneous frustration parameters in spin-liquids.
- The results depend upon choice of fitting method and temperature range used.
- More appropriate method is to use a ʽrange of fit' analysis.
- Can distinguish between spin-liquids and correlated paramagnets.

Absence of a single smoking-gun experiment to identify a quantum spin liquid, has kept their characterisation difficult till date. Featureless dc magnetic susceptibility and large antiferromagnetic frustration are always considered as the essential pointers to these systems. However, we show that the amount of frustration estimated by using generalised Curie-Weiss law on these susceptibility data are prone to errors and thus should be dealt with caution. We measure and analyse susceptibility data of Ba3ZnIr2O9, a spin orbital liquid candidate and Gd2O3, a 1.5 K antiferromagnet and show the distinguishing features between them. A continuous and significant change in Curie and Weiss constants is seen to take place in Ba3ZnIr2O9 and other reported spin liquids with the change in the range of fitting temperatures showing the need of a temperature 'range-of-fit' analysis before commenting on the Weiss constants of spin liquids. The variation observed is similar to fluctuations among topological sectors persisting over a range of temperature in spin-ice candidates. On the other hand, even though we find correlations to exist at even 100 times the ordering temperature in Gd2O3, no such fluctuation is observed which may be used as an additional distinguishing signature of spin liquids over similarly featureless correlated paramagnets.

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