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Scheme for broad band detection of low-field Larmor precession. A short polarization field, , of typically duration generates a magnetization along the axis. After switching off the polarization field, the magnetization begins to precess about the axis of the detection field, . The corresponding variation of the component of the magnetization is measured by the SQUID gradiometer above the sample.
(a) FID of at a detection field of averaged over 50 samples and (b) the corresponding spectrum obtained by complex Fourier transformation of the FID after zero filling from . The measured spectrum is plotted by circles, the solid line shows the Lorentz line shape fit.
Width of the Lorentz line of water in the low-field range The linewidth increases slightly with the detection field due to its increasing absolute inhomogeneity. The uncertainty bars reflect the standard deviation of the Lorentzian fit. The deviation from the linear behavior for the measurement may be attributed to increased noise.
and spectrum of trifluoroethanol at a low detection field, i.e., at flux density. Trifluoroethanol has a molecular structure similar to ethanol except that the methyl protons are exchanged by fluorine. In contrast to ethanol, where all nuclei are magnetically equivalent, heteronuclear J-coupling between and of trifluoroethanol results in structured spectra with several peaks.
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