Chapter 12 studies the property of magnetic response functions of electrons probed by nuclear magnetic resonance (NMR) experiments. The Knight shift is shown to be proportional to the real part of the local magnetic susceptibility. The spin-lattice relaxation, on the other hand, provides an effective measure of the imaginary part of the susceptibility averaged by the interaction form factor over the whole Brillouin zone. The effect of impurity scattering, particularly the impurity induced resonance states, on the NMR spectra is discussed and compared with experimental results.

We shall first outline the types of interactions of spins, which are most important for solid polarized targets: the magnetic dipole interaction, the quadrupole interaction, the spin-orbit interaction and the hyperfine interaction. Other direct and indirect spin interactions are described: these give rise to the chemical shift, the Knight shift, molecular spin isomers and to the exchange interaction of electron pairs. These, and in particular the dipolar interaction, are then used in the discussion of the magnetic resonance phenomena, such as the resonance line shape and saturation. The magnetic resonance absorption and the transverse susceptibility are discussed starting from the first principles, and Provotorov's equations are derived. The relaxation of spins, which is phenomenologically introduced already for the saturation, is then overviewed in greater depth, before closing with sudden and adiabatic changes of spin systems in the rotating frame.