g Factors and Spin-Lattice Relaxation of Conduction Electrons

This chapter is concerned with spin-resonance absorption—that is, power absorption from an oscillating magnetic field—by conduction electrons. The e place of spin resonance in investigations of the band structure contrasts the cases of paramagnetic salts and conductors. In the former, the levels of the ions are discrete; when they have an odd number of electrons each level is at least twofold degenerate. An external magnetic field splits this degeneracy. The microwave spectroscopy of the energy bands is not confined to spin resonance, but includes cyclotron resonance. Of the two, undoubtedly the latter provides the most direct information on the energy bands. Spin resonance does not play the central role that it does in paramagnetic salts. However, it usually plays a useful supplementary role when something about the band structure is known, serving either as a check on the band model or determining the values of additional parameters. The use of spin resonance in semiconductors and semimetals grow as better materials are made and detailed knowledge about their band structure becomes available.