The nonlinear susceptibility is discussed as a probe of multispin correlation functions. In the heavy-fermion compound URu2Si2, measurements of the leading nonlinear susceptibility (3) reveal a sharp anomaly at 17.3 K closely matching that of the specific heat at the same temperature. We attribute this result to the development of anisotropic triplet pairing in the particle-hole channel of the heavy electron fluid. © 1992 The American Physical Society.

We discuss the nonlinear susceptibility (χ3) as a probe of higher-order spin correlations in heavy fermion materials, with particular emphasis on U Ru2Si2 and U Be13. The sharp discontinuity of χ in U Ru2Si2 is contrasted with two other antiferromagnets U2Zn17 and U0.95Th0.05Pt3 with larger moments. Nonlinear magnetic properties of URu2Si2 can be understood simply in terms of Landau-Ginzberg theory for a large hidden, itinerant order parameter. In UBe13 we discuss how χ3 can be used to probe the presence of quadrupolar fluctuations. © 1994.