Theory of conduction-electron spin resonance

Abstract

The influence of the conduction-electron magnetization density, induced in a metallic slab by an incident microwave electromagnetic field, on the power absorbed from the microwave field, and on the field transmitted through the slab, is studied theoretically. The motion of the magnetization density is described by a Bloch equation, modified to include diffusion; this approach is equivalent to, but simpler than, that of Dyson. For classical skin effect conditions, exact formulas for the amplitudes of the transmitted fields and for the surface impedance are obtained for symmetric excitation, for antisymmetric excitation, and for one-sided excitation. In performing the calculations, it is found to be convenient to separate the magnetization density into two parts, a forced part and a free part; the forced part is the more important in the slow-diffusion limit, while the free part is the more important in the rapid-diffusion limit. A calculation of the amplitude of the transmitted field, valid under anomalous skin effect conditions, is given for the limiting cases where the diffusion is either very rapid or very slow. Also, the dependence of the polarization of the transmitted fields on the angle which the static applied magnetic field makes with the normal to the slab is discussed.