Superconducting magnet

NMR spectra were obtained with a Tecmag Apollo spectrometer and a standard sample probe from NMR Service GmbH. The magnetic field has been applied by a 16 T Oxford Instruments superconducting magnet. Temperatures were regulated by a ⁴He variable temperature insert (VTI). Temperatures below 4.2 K were achieved by pumping on the VTI. At high temperatures and small fields, Fourier transformations (FFT) of the spin echo covered the whole spectral width. At lower temperatures, we swept the frequency and summed up the FFT’s to obtain the complete spectrum. The spectra at 15 T below 10 K have been obtained by field sweeps, and converting into frequency sweeps. This is easily possible due to the negligible quadrupole interaction. We have confirmed the correctness of this procedure at higher temperatures. The spin lattice relaxation rate, $T_1^{-1}$ , has been measured by standard saturation recovery at the peak of the spectra. The nuclear magnetization, M₀, has been saturated by a train of radio frequency pulses, before measuring the recovered nuclear magnetization, M(τ), depending on the time τ between the saturation train and the spin echo sequence.