Diagnosis of quantum criticality by nuclear spin‐echo decay method

The Gaussian spin–spin relaxation time T 2G , as determined by nuclear magnetic resonance (NMR) spin‐echo decay measurements, is found to be useful for diagnosis of quantum critical behaviour in heavy‐fermion systems. Combining T 2G with the spin–lattice relaxation time T 1 , the exponent ϕ of the quantity $T_1 T/T_{2G}^2 \sim T^\phi$ is predicted to be sensitive to the type of quantum criticality in the system concerned. In fact, in the heavy‐fermion system USn 3 near the quantum critical point, $T_1 T/T_{2G}^2$ is found to be constant, as expected for a 3D‐SDW magnetic instability.