NUCLEAR-MAGNETIC-RESONANCE AND RELAXATION IN THE SPIN-WAVE REGIME OF THE DIPOLAR HEISENBERG-FERROMAGNET EUS

We have investigated the resonance frequency f(tau) the longitudinal a nd the transverse relaxation rates T1(-1), T2(-1), of Eu-153 in fields up to 2 T for low temperatures, T < 4.2 K << T(c) = 16.5 K. Based on exchange constants from neutron data, a detailed analysis of the field dependence of f(r) reveals a magnetic anisotropy field B(a) = 4 mT pa rallel to [100], which is much smaller than that proposed in previous NMR work but which is consistent with early ferromagnetic-resonance re sults. T1(-1) appears to be dominated by the dipolar-induced two-magno n relaxation. First evidence for a significant on-site contribution of the Suhl-Nakamura interaction to T2(-1) is provided, caused by the ve ry small spin-wave stiffness in this material.