| Summary: | We report beta-NMR measurements of the nuclear spin relaxation rate (1/T-1) in a thin film of La0.67Ca0.33MnO3 (LCMO) using a low-energy beam of spin-polarized Li-8. In a small magnetic field of 150 G, there is a broad peak in 1/T-1 near the Curie temperature (T-c = 259 K) and a dramatic decrease in 1/T-1 at lower temperatures. This is attributed to a critical slowing down of the spin fluctuations near T-c 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 Li-8 in the SrTiO3 substrate. There is an indication that the spin relaxation rate in the substrate is also peaked at T-c due to close proximity to the magnetic film. These results establish that low-energy beta-NMR can be used as a probe of magnetic fluctuations in magnetic thin films over a wide range of temperatures. (c) 2005 Elsevier B.V. All rights reserved.
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