Nuclear spin relaxation of 8Li in a thin film of La0.67Ca0.33MnO3

We report ββ-NMR measurements of the nuclear spin relaxation rate (1/T1)(1/T1) in a thin film of La0.67Ca0.33MnO3 (LCMO) using a low-energy beam of spin-polarized 8Li. In a small magnetic field of 150 G, there is a broad peak in 1/T11/T1 near the Curie temperature (Tc=259K) and a dramatic decrease in 1/T11/T1 at lower temperatures. This is attributed to a critical slowing down of the spin fluctuations near TcTc and freezing of the magnetic excitations at low temperatures, respectively. In addition, there is a small amplitude, slow relaxing component at high temperatures, which we attribute to 8Li in the SrTiO3 substrate. There is an indication that the spin relaxation rate in the substrate is also peaked at TcTc due to close proximity to the magnetic film. These results establish that low-energy ββ-NMR can be used as a probe of magnetic fluctuations in magnetic thin films over a wide range of temperatures.