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

Abstract

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

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

“…4). Thus, a priori, it is not clear how useful 8 Li β-NMR will be in strongly magnetic materials, though there are a few reports in ferromagnets [27,[33][34][35]. The present results provide another example where, at low temperature, the combination of the high applied field and the weak hyperfine coupling of 8 Li make the relaxation in EuO measurable at low temperature.…”

“…Upon implantation, the spin polarization of a particular ion in a specific local environment often relaxes as a single exponential p(t) = exp(−λt), where λ ≡ 1/T 1 . Averaging this relaxation over all arrival times convolutes the square beam pulse with p(t), yielding the characteristic β-NMR relaxation function that falls from its initial value at the start of the beam pulse (t = 0) to the pronounced kink at the end of the pulse [27,28], with subsequent relaxation of the remaining 8 Li spins afterwards, e.g., see Figs. 1 and 2 below.…”

Low-field cross spin relaxation ofL8iin superconductingNbSe2

“…Excellent fits to the normal state data were obtained assuming single exponential relaxation for a 8 Li spin arriving at time tЈ, and detected later at time t, i.e., p͑t − tЈ͒ = exp͓−͑t − tЈ͒ / T 1 ͔. The fitted curves are obtained by weighting p͑t − tЈ͒ according to the radioactive decay of the 8 Li and integrating over arrival times tЈ Ͻ t. 17,18 One then obtains an average polarization for all the 8 Li in the sample at time t,…”

“…The beam was focused such that there was no detectable background signal. 10 A long pulse method [16][17][18] was used to measure 1 / T 1 of the 8 Li, in which a period of 4 s of beam on is followed by 12 s of beam off. Figure 3 shows the typical time dependence of the beta-decay asymmetry AP͑t͒ over the full time interval, where A is an experimental constant determined by the properties of the beta decay, geometry, and degree of polarization and P͑t͒ is the nuclear polarization averaged over all 8 Li in the sample and normalized such that P͑0͒ = 1.…”

Proximal magnetometry in thin films using NMR

“…For these reasons, it is interesting to consider what information might be obtained by ''implanted ion proximal magnetometry'' (IIPM). We note several experiments along these lines have already been accomplished using bNMR [4,[8][9][10], and that IIPM is similar to NMR and EPR decoration experiments (the analogue of Bitter decoration of a superconductor) [11] and the use of adsorbed layers of hyperpolarized 129 Xe [12], but with the advantage of an easily controlled probe depth and a thin film geometry. We discuss this application in Section 4 and illustrate the results with experimental data in Section 5.…”