We present a tutorial on the cross-polarization experiment, which has been the main method of magnetization transfer in solid-state NMR for decades. We explain the principles of its volume-selective performance in the presence of magic angle spinning and radiofrequency field inhomogeneity and the decrease in efficiency with increasing sample rotation frequency.

Dynamic nuclear polarization requires a waveguide that connects the cold (1–10 K) sample space to the outside. To reduce the heating of the sample, a waveguide is produced from steel which has low thermal conductivity but attenuates the microwaves. Therefore, the inside of the waveguide should be plated with silver to reduce electrical losses. We show a new simple way to electroplate such waveguides with a thin silver layer and show that this improves the experimental performance.

Dynamic nuclear polarisation (DNP) transfers polarisation from electron to nuclear spins. This is usually combined with direct detection of the latter. Here, we show that it is possible to reverse the transfer at 1.2 T. This allows us to investigate the spin dynamics of nuclear spins close to electrons – something that is notoriously difficult with established methods. We expect reverse DNP to be useful in the study of spin diffusion or as a building block for more elaborate pulse sequences.

Through the advent of fast magic-angle spinning and high magnetic fields, the spectral resolution of solid-state NMR spectra has recently been greatly improved. To take full advantage of this gain, the magnetic field must be stable over the experiment time of hours or even days. We thus monitor the field by simultaneous acquisition of a frequency reference (SAFR) and use this information to correct multidimensional spectra improving resolution and availability of productive magnet time.

The radio-frequency (rf) field amplitude in solid-state NMR probes changes over the sample volume, i.e. different parts of the sample will experience different nutation frequencies. If the sample is rotated inside the coil as it is typical for magic angle spinning in solid-state NMR, such a position-dependent inhomogeneity leads to an additional time dependence of the rf field amplitude. We show that such time-dependent modulations do not play an important role in many experiments.

Sample rotation around the magic angle averages out the dipolar couplings in homonuclear spin systems in a first-order approximation. However, in higher orders, residual coupling terms remain and lead to a broadening of the spectral lines. We investigate the source of this broadening and the effects on the powder line shape in small spin systems with and without chemical shifts. We show that one can expect different scaling behavior as a function of the spinning frequency for the two cases.

Measuring distances between unpaired electron spins is an important application of electron paramagnetic resonance. The longest distance that is accessible is limited by the phase memory time of the electron spins. Here we show that strong continuous microwave irradiation can significantly slow down relaxation. Additionally, we introduce a phase-modulation scheme that allows measurement of the distance during the irradiation. Our approach could thus significantly extend the accessible distances.

This paper analyzes a commonly used line-narrowing mechanism (homonuclear decoupling) in solid-state NMR and discusses what limits the achievable line width. Based on theoretical considerations, the contribution of different effects to the line width is discussed and a new contributing term is identified. This research allows us to evaluate new ways to improve the line width in such homonuclear decoupled spectra.