β-detected NMR spin relaxation in a thin film heterostructure of ferromagnetic EuO

We present beta-detected NMR measurements of the spin-lattice relaxation of Li-8(+) implanted into an epitaxial heterostructure based on a 100 nm thick film of ferromagnetic (FM) EuO as a function of temperature through its FM transition. In the FM state, the spin-lattice relaxation rate follows the same temperature dependence, determined by magnon scattering mechanisms, observed in the bulk by Eu-153 NMR, but above 40 K, the signal is wiped out. We also find that Li-8(+) stopped in material adjacent to the magnetic layer exhibits spin relaxation related to the critical slowing of the Eu spins. A particularly strong relaxation in the Au overlayer suggests an unusual strong nonlocal coupling mechanism to Li-8 in the metal.