Propagation, of magnetisation

Figure 5.58. The TOCSY spectrum of 5.1, Relayed crosspeaks are apparent between spins that lack direct scalar couplings but which exist within the same spin-system and arise from the propagation of magnetisation along the chain of coupled spins. Compare this with the COSY spectrum in Fig. 5.12.

Figure 5.64. Schematic illustration of the propagation of magnetisation along a chain of coupled spins as a function of the spin-lock mixing time. The arrows indicate the cyclic exchange of coherence between nuclei.

Figure 5.67. The time-dependent propagation of magnetisation along a proton spin system as illustrated for the ornithine residue of Gramicidin-S. Traces are extracted from 2D MLEV-17 TOCSY spectra at the amide NH proton shift and show progressive transfer along the sidechain as the mixing time increases.

Fig, 5.8 Predicted spectra using an iron metal source at room temperature magnetised perpendicular to the axis of propagation. 

A wave can be propagated through the material by means of this mechanism, Fig. 4.45(c). In a similar way to phonons (quantised mechanical vibrations of the lattice), magnons can be thought of as particles, with all their associated properties and interactions. Spin wave theory (Bloch, 1930) provides an interpretation of the low-temperature behaviour of saturation magnetisation in ferromagnets. 

---