In a high-temperature, classical paramagnet phase, the magnetic susceptibility is given by the Curie–Weiss law
Fitting experimental data to this equation determines a phenomenological Curie–Weiss temperature, .  There is a second temperature, , where magnetic order in the material begins to develop, as evidenced by a non-analytic feature in . The ratio of these is called the frustration parameter
In a classic antiferromagnet, the two temperatures should coincide and give . An ideal quantum spin liquid would not develop magnetic order at any temperature  and so would have a diverging frustration parameter . A large value  is therefore a good indication of a possible spin liquid phase.  Some frustrated materials with different lattice structures and their Curie–Weiss temperature are listed in the table below. All of them are proposed spin liquid candidates.