Observation of non-exponential relaxation above TN in the dilute Heisenberg antiferromagnet KMn0.3Ni0.7F3

The authors investigate the dynamics above TN (210 K) of the dilute Heisenberg antiferromagnet KMn0.3Ni0.7F3 using neutron inelastic scattering. They find evidence for a long-time tail in the relaxation function at all temperatures above TN with relaxation being much slower at and below the so-called Griffiths temperature TG (246 K) which is the ordering temperature of pure KNiF3. This is as predicted by recent theoretical studies.