Nuclear-Magnetic-Resonance Echo Enhancement in an Antiferromagnet

The observation of an anomalous enhancement of a two-pulse nuclear spin echo in antiferromagnetic MnO by a prepulse of variable width, amplitude, and delay time is described. A theory explaining this observation by adding frequency pulling to the Bloch equations is discussed. In this model the frequency pulling parameter is assumed to be inhomogeneous throughout the sample, consistent with current ideas of NMR line broadening in materials with strong pulling. Long free-induction decays observed following wide pulses are also explained.