The temperature and magnetic-field (H) dependencies of the bulk dc magnetization (M) and the M/H ratio of montmorillonite (MMT), hectorite (HCT), and synthetic mica-montmorillonite (SMMT) clays have been measured and compared with the signal intensity of 1H and 29Si nuclear magnetic resonance (NMR) spectra. MMT exhibits Langevin paramagnetism with an effective magnetic moment of 5.5±0.1 μ B per Fe ion whereas SMMT has diamagnetic properties. At 300 K, M/H of HCT measured in a magnetic field of H≤ 1 kOe is larger than that of MMT, whereas in a field of 50 kOe, the inverse situation is observed. The difference arises because the magnetization of HCT is dominated by a contribution from ferromagneticlike impurities. The 1H and 29Si NMR signals of MMT are broadened beyond detectability due to the paramagnetic effect. Although HCT contains ferromagneticlike components that result in a large M/H in low field, it yields 1H and 29Si NMR spectra with signal intensities similar to those of diamagnetic SMMT. Our data highlight that the quality of the NMR spectra is not related to the low-field magnetic susceptibility but to the bulk magnetization in the high magnetic field used for NMR.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)