Transverse Nuclear Relaxation in Real Ferromagnets

The existing theoretical model proposed by Hone, Jaccarino, Ngwe, and Pincus (HJNP) to treat spin-spin relaxations in inhomogeneous lines is extended in order to make it applicable to experimental situations often encountered in real ferromagnetic systems. The transverse relaxation of ${\mathrm{Eu}}^{151,153}$ in ferromagnetic EuO and of ${\mathrm{Co}}^{59}$ in ferromagnetic Co metal was studied by the spin-echo technique as function of external magnetic field $H_0>4\mathrm{}\pi M$ at low temperatures. Nonexponential echo decays were observed in all cases and the relaxation rates were found to be field dependent. The extended HJNP model was successfully applied to account for the observations in EuO, verifying in a quantitative manner the important role played by the indirect spin-spin (Suhl-Nakamura) interaction in the relaxation processes of this system. The analysis also yields detailed information concerning the character of the local distribution of the effective fields acting on Eu nuclei in EuO.